College of Agriculture & Natural Resources
Plant Science & Landscape Architecture

Plant Science Theses and Dissertations

Ever wonder what kind of thesis projects our students worked on while here in our program? Check out the topics our students, now alumni, explored!

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Katelin Marie Posthuma

Kintsugi: A New Framework For Post-Industrial Transformation 

This thesis uses the Morse Chain factory in Ithaca, New York as a testing ground for the development and exploration of the kintsugi framework as a method for transformation of large-scale postindustrial sites. Deindustrialization has had a profoundly destabilizing effect on many communities that were depended on industry. Abandoned industrial facilities are one of the primary visual markers of deindustrialization. Landscape architects employ two strategies for reclaiming these spaces - the conceal/camouflage approach or the reveal/reinterpret approach. These two approaches are typically presented in opposition to each other, which limits the design potential of these sites The kintsugi framework blends these two operating modes, creating an exciting and interesting operating field for the transformation of post-industrial sites. Based on the traditional Japanese method of repairing broken pottery with gold inlay. This technique incorporates damage as the central element for metamorphosis and change.

 Jun Zhang 


Auxin is a crucial plant hormone that shapes and directs plant growth. Indole-3-acetic acid (IAA) is the predominant auxin in nature. Auxin regulates cell expansion and cell division in a dose dependent way. Therefore, plants evolved an extremely complex yet highly coordinated network to maintain auxin homeostasis, including IAA biosynthesis, transport, conjugation and oxidation. Among these, the least known process is IAA oxidation. Discovering how IAA is terminated is very important in completing the whole picture of IAA homeostatic regulation. By partial purification of IAA oxidases from Arabidopsis, we detected IAA oxidation activity from both microsomal fractions and soluble fractions. We first investigated the protein in microsomal fraction and identified one oxidase named as ACC oxidase 2 (ACO2), an ethylene synthetase that belongs to 2-oxoglutarate and iron (II) [2OG(Fe)] dependent dioxygenase family. In vitro enzyme assays with IAA showed that ACO2 could catabolize IAA and that the product had the same retention time as indole-3-carbinal (ICA), an decarboxylative IAA oxidation product. The same enzyme assay with the ACO2 homologues ACO3 was conducted, and ACO3 showed similar activity. An ACO2 loss-of-function allele showed ethylene related phenotypes, including longer hypocotyls and reduced apical hook angle in etiolated seedlings, and delayed bolting. Further, null aco2 mutants also showed reduced phototropic bending, a typical auxin related phenotype. These results indicate that ACO2 might be involved in both ethylene and auxin signaling. We also investigated the soluble IAA oxidases, AtDAO1 (DAO1) and AtDAO2 (DAO2). In vitro enzyme assays showed that both recombinant DAO1 and DAO2 have IAA oxidation activity and the product is the non-decarboxylated 2-oxindole-3-acetic acid (oxIAA), the major IAA metabolite observed under normal growth conditions. Analysis of the loss-of-function null allele dao1-1 showed that DAO1 is the predominant IAA oxidase and is responsible for 95% of oxIAA production in Arabidopsis seedlings. Dysregulation of IAA oxidation altered the IAA metabolism profile and causes accumulation of other IAA conjugates and a series of morphological alteration, including elongation of organs, increased lateral roots and delayed sepal opening. Investigation of expression patterns shows that DAO1 is a cytosolic protein that widely expressed throughout the plant, especially in the root tip, the pericycle of root, the cotyledon, and the sepal, highly correlating to the phenotypes of dao1-1. These results suggest that IAA oxidation plays an important role in IAA homeostasis during the whole life of Arabidopsis.

Cody Kepher 


Fungal fruit rots and insect pests are among the most important problems negatively affecting the yield and quality of mid-Atlantic wine. In pathogenicity trials of fungi recovered from diseased Chardonnay and Vidal blanc grapes, Alternaria alternata, Pestalotiopsis telopeae, and Aspergillus japonicus were found to be unreported fruit rot pathogens in the region. Additionally, P. telopeae and A. japonicus had comparable virulence to the region’s common fruit rot pathogens. Furthermore, a timed-exclusion field study was implemented to evaluate vineyard insect-fruit rot relationships. It was found that clusters exposed to early-season insect communities that included Paralobesia viteana had a significantly greater incidence of sour rot than clusters protected from insects all season. These results were contrary to the current assumption that fall insects are the primary drivers of sour rot in the region. This research provides diagnostic tools and information to develop management-strategies against fungal and insect pests for mid-Atlantic grape growers.

Sarah Michelle Allard 

Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation 

Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.

Jun Jiang 


This design-research thesis suggests that the improvement of North East Street performances by using Complete Streets, Green Street, Place Making and Context Sensitive Solution principles and practices. Heavily used by a variety of users, often conflicting with one another, University of Maryland Campus Drive would benefit from a major planning and design amelioration to meet the increasing demands of serving as a city main street. The goal of this thesis project is to prioritize the benefits for pedestrians in the right-of-way and improve the pedestrian experience. This goal also responds to the recent North East Street Extension Phrase I of economic renaissances. The goal of this design-research thesis will be achieved focusing on four aspects. First, the plans and designs will suggest to building mixed use blocks, increase the diversity of street economic types and convenience of people’s living. Second, design and plans will propose bike lanes, separate driving lanes from sidewalks and bike lanes by street tree planters, and narrow driving lanes to reduce vehicular traffic volume and speed in order to reduce pedestrian and vehicle conflicts. Third, plans and designs will introduce bioswales, living walls and raingardens to treat and reuse rain water. Finally, the plans and designs will seek to preserve local culture and history by adding murals and farmers market. The outcome of the design-research thesis project is expected to serve as an example of implementing Complete Streets, Green Street, Place Making and Context Sensitive Solution principles and practices in urban landscape, where transportation, environment and social needs interact with each other.

Laura Kristine Templeton 

Changes in the community structure of urban and rural forest patches in Baltimore from 1998 to 2015 

Urban forests are often highly fragmented with many exotic species. Altered disturbance regimes and environmental pollutants influence urban forest vegetation. One of the best ways to understand the impacts of land-use on forest composition is through long-term research. In 1998, the Baltimore Ecosystem Study established eight forest plots to investigate the impacts of urbanization on natural ecosystems. Four plots were located in urban forest patches and four were located in rural forests. In 2015, I revisited these plots to measure abundances and quantify change in forest composition, diversity, and structure. Sapling, shrub, and seedling abundance were reduced in the rural plots. Alpha diversity and turnover was lower in the rural plots. Beta diversity was reduced in the rural plots. The structure of the urban plots was mostly unchanged, except for a highly reduced sapling layer. Beta diversity in the urban plots was consistent across surveys due to high species turnover.

Nathan Allen 


This thesis demonstrates how landscape architects can transform underused golf course facilities located within cities for urban agriculture (UA). In the last decade more than 1000 golf courses have closed in the United States. Municipal golf courses represent some of the largest pieces of open space in cities and because of their inherent infrastructure they can provide the ideal location to support large-scale UA. In Southwest Baltimore large food deserts are a serious health concern and represent a lack of access to healthy food options for residents. Carroll Urban Agriculture Park is a design response resulting from a detailed analysis of the existing Carroll Park Golf Course and the surrounding community of Southwest Baltimore. The design will create an urban farm in a park-like setting to provide readily accessible healthy food options and various educational opportunities, and to support current and future urban agriculture related businesses in Baltimore.

Amina Ibrahim Mohamed 


This thesis addresses contemporary gaps of vacancy within literature by using qualitative and quantitative methods and tools to determine the quantity, location, and interspatial relationships of vacant buildings and lots located in Baltimore Maryland. Spatial analyses were conducted to answer three questions of vacancy: 1) how many vacant lots and buildings exist, 2) whether there are spatial patterns of vacancy, such as clustering around geographic locations or within watersheds, and 3) how to prioritize intervention opportunities that respond to the city's larger issues? Using the city’s vacant lot and building data-sets, two concepts emerged from these investigations. First, Utilized Landscapes as a classification system that identifies lands that serve a function but have un-traditional qualities that make them susceptible to being labeled “vacant.” Second, the development of Transitional Zones, geographical areas with a high density of vacant buildings or lots that should be prioritized.

George Sorvalis 


This paper answers the question of whether a design intervention on Washington Adventist Hospital’s Takoma Park campus can combine stormwater Best Management Practices with outdoor healing spaces, to improve the health of the local creek (Sligo Creek) while creating a restorative environment for the hospital community. To improve the health of Sligo Creek, a campus-wide stormwater analysis was undertaken, in addition to an intervention-site-specific stormwater analysis, and a literature review of stormwater best management practices. To create a restorative environment, a literature review of healing gardens was undertaken, in addition to a campus-wide site analysis, to uncover the most ideally suited site to create a restorative environment.

Kathleen Hayes 

Regenerative Stormwater Conveyance: Design Implications of an Urban Case Demonstration in Baltimore, Maryland 

This research-design thesis explores the implementation of Regenerative Stormwater Conveyance (RSC) as a retrofit of an existing impervious drainage system in a small catchment in the degraded Jones Falls watershed in Baltimore City. An introduction to RSC is provided, placing its development within a theoretical context of novel ecosystems, biomimicry and Nassauer and Opdam’s (2008) model of landscape innovation. The case site is in Baltimore’s Hampden neighborhood on City-owned land adjacent to rowhomes, open space and an access point to a popular wooded trail along a local stream. The design proposal employs RSC to retrofit an ill-performing stormwater system, simultaneously providing a range of ecological, social and economic services; water quantity, water quality and economic performance of the proposed RSC are quantified. While the proposed design is site-specific the model is adaptable for retrofitting other small-scale impervious drainage systems, providing a strategic tool in addressing Baltimore City’s stormwater challenges.

Xiayun Xiao 


High volume compost incorporation can reduce runoff from compacted soils but its use also associated with elevated N and P concentrations in runoff making it difficult to assess if this practice will reduce nutrient loading of surface waters. Additionally, little is known about how this practice will effect leguminous species establishment in lawns as means to reduce long term fertilizer use. When 5 cm of compost was incorporated into soil a reduction in runoff of 40 and 59% was needed for N and P losses from a tall fescue + microclover lawn to be equivalent to a non-compost amended soil supporting a well fertilized tall fescue lawn. Use of compost as a soil amendment resulted in quicker lawn establishment and darker color, when compared to non-amended soil receiving a mineral fertilizer. Biosolid composts containing high amounts ammonium severely reduce the establishment of clover in tall fescue + micrclover seed mixture.

Chioma Egekwu 

Influence of Nitrogen and Sink Competition on Shoot Growth of Poplar 

Terrestrial and oceanic biomass carbon sinks help reduce anthropogenic CO2 emissions and mitigate the long-term effect of increasing atmospheric CO2. Woody plants have large carbon pools because of their long residence time, however N availability can negatively impact tree responses to elevated CO2. Seasonal cycling of internal N in trees is a component that contributes to fitness especially in N limited environments. It involves resorption from senescing leaves of deciduous trees and storage as vegetative storage proteins (VSP) in perennial organs. Populus is a model organism for tree biology that efficiently recycles N. Bark storage proteins (BSP) are the most abundant VSP that serves as seasonal N reserves. Here I show how poplar growth is influenced by N availability and how growth is influenced by shoot competition for stored N reserves. I also provide data that indicates that auxin mediates BSP catabolism during renewed shoot growth. Understanding the components of N accumulation, remobilization and utilization can provide insights leading to increasing N use efficiency (NUE) of perennial plants.


Nicholas William Yoder

Changing Course: Repurposing Golf Landscapes for Wildlife Habitat and Recreation 

More than 1,400 golf facilities in the United States have closed permanently since 2001, part of a natural supply correction, as well as a reflection of the fluctuating interest in the game. Through their design, golf courses inherently preserve a singular form of open, green space. In their most dynamic form, they are culturally integral landscapes with vibrant ecosystems that provide wildlife habitat. They represent some of the largest ‘undeveloped’ spaces in United States’ cities. Each golf course closing represents a single patch of many that, with sound design, could be woven together through a common purpose, like a landscape quilt. Through a site-specific analysis, the resulting design proposal for Wakefield Wildlife Reservation is a new type of landscape for the city of Westminster, MD, serving as an example for future projects. It will provide valuable habitat and dynamic recreational space, while expressing site and regional history.

 Daniela Michelle Miller 

Genetic Control of Flowering Time in a Soft Red Winter Wheat Doubled Haploid Population 

Flowering time in wheat is regulated mainly by response to seasonal environmental cues and controlled by the photoperiod and vernalization pathways. Allelic diversity in genes controlling these pathways is used by breeders to adapt wheat for optimal yield in a broad range of environments. This study characterized genetic loci influencing heading date in a soft red winter wheat doubled haploid population. Two photoperiod insensitivity alleles, Ppd-A1a and Ppd-D1a, were found to have major effects in eight field locations. The Ppd-A1 locus explained up to 16.8% of variation in heading date, whereas the Ppd-D1 locus explained up to 39.7%. In reduced vernalization greenhouse experiments, a QTL in the same region as the VRN-A1 gene explained up to 42.4% of variation in heading date, suggesting that the population differed in this region. Assays for previously-described allelic diversity in the VRN-A1 gene, however, did not detect any polymorphism between parents of the population.

Siqi Chen 


Compost topdressing, compost tea, and hollow tine cultivation are common cultural practices employed in organic lawn care programs. Restrictions on the amount of bagged fertilizer nitrogen and phosphorus applied to turf have raised questions about the need to place similar restrictions on compost turfgrass applications. In a three-year study the effect of reduced and common practitioner use rates of compost topdressing, the use of compost tea and of hollow tine cultivation on soil physical and biological properties and turfgrass quality were evaluated. Cultivation, monthly compost tea application and compost topdressing applied at rates consistent with annual bagged fertilizer nitrogen restrictions had little effect on soil organic matter, microbial activity, bulk density and infiltration. The use of a synthetic fertilizer resulted in higher turf quality than the use of compost on most evaluation dates. Nutrient fertilizer restrictions if applied to compost will likely result in a decline in turf quality

Yaopeng Zhou 


Improving wheat grain yield potential is imperative to match the increasing food demand associated with a fast growing population. Genetic and modeling approaches were employed to investigate the genetic basis and phenotype network regarding grain yield and yield related traits in a soft red winter wheat doubled haploid population. The population and two parents were evaluated in five year-location trials in the USA and genotyped by high throughput DNA markers including simple sequence repeat (SSR) and single nucleotide polymorphism (SNP). Bi-parental linkage mapping identified a number of QTLs for grain yield and yield related traits among which sixty were for grain yield components (GYLD, grain yield; SPSM, spikes per square meter; TGW, thousand grain weight; GPS, grains per spike; GWPS, grain weight per spike), seventy four were for plant architecture (PHT, plant height; FLL, flag leaf length; FLW, flag leaf width; FLA, flag leaf area; FLS, flag leaf shape or length/width ratio), and one hundred and nine were for spike morphology (SL, spike length; TSN, total spikelet number per spike; FSN, fertile spikelet number per spike; SSN, sterile spikelet number per spike; SC, spike compactness; GSP, grains per spikelet). In addition, structural equation modeling is described to construct a phenotype network. It revealed that GSP and FSN may mediate yield component compensation. Furthermore, doubled haploid lines DH96 and DH84 may have potential as new high-yielding cultivars for the Mid-Atlantic region.

Sanghyun Han


Several outbreaks of Salmonella enterica infections have been linked to tomatoes. One cost-effective way to complement on-farm preventive Good Agricultural Practices would be to identify cultivars with inherent decreased susceptibility to Salmonella colonization. Various tomato cultivars with distinct phenotypes were screened to evaluate their susceptibility to Salmonella epiphytic colonization. The potential role of plant exudates, collected from the same cultivars, on the growth kinetics of Salmonella was examined. These investigations were supplemented with Salmonella genome-wide transcriptomics that showed bacterial responses to colonization of tomato shoots and roots. Epiphytic colonization of fruit by S. enterica was cultivar-dependent and serotype-specific, but did not correlate with leaf colonization. Fruit and leaves of the same cultivar differed in their ability to support Salmonella growth. Quantitative and qualitative analysis of tomato exudates provided a possible explanation for the differential susceptibility to bacterial colonization among tomato cultivars. Tomato exudates alone were capable of supporting Salmonella growth, and the growth kinetics of Salmonella in tomato exudates differed by cultivar. Characterization of the chemical composition of primary and secondary metabolites in tomato exudates pointed to potential causes for the differential growth of Salmonella observed in the exudates of various tomato cultivars. Key transcriptomic signals that were down- and up-regulated in Salmonella upon interacting with tomato were identified, enabling us to elucidate the molecular mechanisms underlying this enteric pathogen-plant interaction. Overall, the identified signals lead to a proposed model that depicts the cellular processes needed to preserve cell viability when multiple abiotic stresses in conjunction with low nutrient availability are encountered, while simultaneously repressing unnecessary energy demands or maintaining them at a level equivalent to growth in a nutritious medium. These findings strongly support the hypothesis that plant-regulated mechanisms influence enteric pathogen colonization. It is clear that Salmonella can sense subtle environmental cues brought about by the genotype or physiological state of plants and can respond with distinct patterns of gene expression. Future work should focus on whether this bacterial behavior on plants results from an evolutionary adaptation to use plants as a vector to re-enter animal hosts.

Sydney F. Wallace 

Diversity of Phytophthora Species in Costa Rica's Tropical Forest 

The fungus-like organism Phytophthora includes more than 130 species, most of which are destructive plant pathogens. Information about the occurrence and diversity of Phytophthora species in forest and protected areas are largely unknown. The purpose of this study was to fill in the scientific gap in species biodiversity by conducting a survey in tropical forest ecosystems. The survey was conducted at 10 sites across Costa Rica. Leaves with lesions attached to live plants (LP), fallen from tree canopies (LF), submerged in forest streams (LS) and soil was sampled. Isolate identification was based on a multi-locus (4 mitochondrial and 4 nuclear) phylogeny, and examination of morphological features. In total 258 isolates were characterized into 21 species: eight known and 13 novel species. Phylogenetically, species discovered were placed in seven different clades and clade 9 included the most number of species. Species were more common in transitional forests. The number of unknown species discovered suggests that tropical forests are a “hotspot “for Phytophthora diversity.

Harris Brian Trobman 


The focus of this thesis is the design and implementation of a community health project at a new school campus for 600 students in St. Louis Du Norde, Haiti. The design harvests and filters rainwater to drinking water standards, grows nutritional vegetable crops on secure rooftops, creates social space, and recycles old tires, plastic bottles and rice sacks that otherwise pose a massive solid waste problem in Haiti. The processes are also taught to the students so they can take and use the planters at home. The materials for building the growing containers and the growing media are all free and made from local wastes (tires, plastic bottles, rice sacks, manure, soil etc.). They are easy to build and free to construct making them accessible to even to the poorest and neediest families in Haiti. The idea is to develop easily replicable and desirable solutions to the basic health needs.

Jonathan Gemmell 

Rethinking Playgrounds: A Design Investigation of Playscape Theory 

This thesis studies how playscapes and nature play offer alternatives to traditional playground designs by encouraging multiple facets of childhood development. Playscapes promote play spaces that integrate physical, mental, and educational features. Harnessing the malleability of the natural landscape provides clear developmental advantages that surpass traditional structure-based playground design and provide opportunities for building environmental literacy. After combining research with feedback taken from site users, a design will be proposed for the exterior of Riverdale Elementary School, in Riverdale Maryland. Anacostia Watershed Society has received a grant for implementing stormwater controls and improving the quality of the nearby Wells Run stream. The design of this project will show how it will be possible to combine playscape, nature play, and environmental literacy goals with stormwater storage and treatment to transform the school's environment.

Justine Beaulieu 

Genotypic Diversity of Common Phytophthora Species in Maryland Nurseries and Characterization of Fungicide Efficacy 

The genetic diversity of P. plurivora, P. cinnamomi, P. pini, P. multivora, and P. citrophthora, five of the most common species found in Maryland ornamental nurseries and mid-Atlantic forests, was characterized using amplified fragment length polymorphism (AFLP). Representative isolates of genotypic clusters were then screened against five fungicides commonly used to manage Phytophthora. Three to six populations were identified for each species investigated with P. plurivora being the most diverse and P. cinnamomi the least. Clonal groups that originated from forest or different nurseries suggest an ongoing pathway of introduction. In addition, significant molecular variation existed for some species among nurseries an indication that unique genotypes being present in different nurseries. Insensitive isolates to fungicides were detected with P. plurivora (13), P. cinnamomi (3), and P. multivora (2). Interestingly, insensitive isolates primarily belonged to the least common genotypic clusters. Because all but two isolates were sensitive to dimethomorph and ametoctradin, the ability of these chemicals to manage Phytophthora is promising. Nevertheless, the presence of two insensitive isolates could portend general insensitivity to these chemicals as well. Results from this study provide a foundation to future population determination and fungicide sensitivity of the plant pathogenic genus Phytophthora in Maryland's ornamental nursery industry.

Elizabeth Taussig Barton 

A Comparison of Organic Matter Amendments for Use in Extensive Green Roof Substrates 

Organic matter is important for water retention and nutrient availability in green-roof systems. Yet few quantitative green-roof studies provide data for various sources of organic matter (OM). Coconut coir (CC), rice hulls (RH), SmartLeaf® (SL), and mushroom compost (MC) were used as green roof substrate amendments. The effects of OM on water-holding capacity, nutrient availability and plant establishment were measured. Growth of Phedimus kamtschaticus was greater with MC or SL compared to CC or RH. Substrate moisture and nutrient availability were significantly affected by OM source during an 8-month rooftop experiment and a 6-month growth chamber study. Coconut coir showed high moisture retention, low nutrient availability and low aboveground biomass, indicating that nutrient availability is crucial to successful plant growth and establishment on a green roof. Composted materials such as MC and SL that have higher levels of available nutrients, promote better growth than unprocessed materials like RH and CC.

Matthew Morris 

Effects of a Simulated Dicamba Misapplication on Non-tolerant Soybeans (Glycine max) 

Approval is pending for the registration of dicamba tolerant (DT) soybeans [Glycine max (L.) Merr.]. The use of dicamba on DT soybeans and other DT crops will increase. Risks associated with dicamba applications include off-target movement to sensitive crops. The objective of this study was to evaluate misapplication of dicamba on non-DT soybeans. Greenhouse and field studies examined a rate titration (0.004 to 0.5 lb ai a-1) of dicamba on non-DT soybeans (V3 stage - three trifoliates). Field studies also examined dicamba application to various growth stages (PRE- preemergence to R5- early pod fill) of non-DT soybeans. Results from the greenhouse and field studies showed that as the rate of dicamba increased, the level of injury to vegetative and yield components also increased. Soybean growth stage at time of application influenced the amount of injury. Less injury was observed when dicamba was applied at the PRE growth stage.


Robyn Edwards 

Choice Experiments and Design Decision-Making 

There is a growing interest in evidence-based design in landscape architecture. This is an exploratory study of the choice experiment method: an economic approach used by many other disciplines but not yet landscape architecture, to collect empirical evidence on the public's preferences for different landscape design characteristics. A choice experiment was conducted for an open space development in downtown Baltimore. The outcomes of the experiment provided a basis for the design of a downtown surface parking lot into a public open space. Design decisions were made with better clarity and confidence that the design solution could maximize utility and value to the public.

Tommy Phannareth 


Salmonella enterica is an enteric human pathogen that lives in gastrointestinal tract; however, Salmonella are able to survive in plants. Thus, vegetables such as tomato are vectors for Salmonella. Evidence suggests that Salmonella induces PAMP-triggered immunity (PTI) in plants, however, plant systemic acquired resistance (SAR), which may act to suppress Salmonella populations, has not been explored. This research investigates whether Salmonella triggers SAR in tomato, and whether SAR activation restricts epiphytic Salmonella populations. Inoculation of tomato leaves with Salmonella increased SAR marker gene expression in distal tomato leaves, but did not reduce populations of the phytopathogen Pseudomonas syringae or Salmonella on distal leaves, even following treatment with chemical SAR activators. NahG plants, which are deficient in SAR signaling, supported higher Salmonella populations, and nitric oxide depletion on leaf surfaces favored Salmonella growth, suggesting that SAR is involved. SAR alone is insufficient to restrict Salmonella growth on tomato, despite being triggered.


Jordan Lee Harris 

Epidemiology and population structure of Xylella fastidiosa, the causal agent of bacterial leaf scorch, among urban trees in the District of Columbia 

A survey of urban trees affected by bacterial leaf scorch caused by Xylella fastidiosa was conducted in the District of Columbia during 2012 and 2013. Disease occurred most frequently with Quercus palustris, Q. rubra, Ulmus americana, and Platanus occidentalis. Eight other symptomatic and five asymptomatic tree species were found infected. The bacterium was also detected on asymptomatic portion of seven tree species. The occurrence of crown dieback was found significantly associated with X. fastidiosa-infection on Q. palustris, Q. rubra, U. americana, and P. occidentalis. A multi-locus sequence typing analysis using 10 housekeeping loci for X. fastidiosa revealed five clonal strains among the urban trees. These strains were host specific, with only one clone being associated with members of the red oak family, American elm, American sycamore, and two clones being associated with mulberry. Long-term management strategies aimed at mitigating the occurrence of bacterial leaf scorch disease are discussed.

Whitney Griffin 


While green roof (GR) systems have gained popularity as storm water management tools, more emphasis has been applied to studying performance aspects, including stormwater retention. Of particular importance is the substrate layer in which the vegetation grows, which contributes the majority of stormwater retention capabilities. This research investigated many aspects of GR substrate performance, including component durability and component effects on hydraulic conductivity, matric potential, and plant growth. Several commercial substrate blends were tested for durability against successive freeze/thaw cycles with before and after-treatment granulometric distribution analyses. All substrate blends showed significant (p<0.05) particle degradation after 30 freeze-thaw cycles, compared to German (FLL) guidelines. The hydraulic conductivity and matric potential of three experimental GR substrates with increasing volumetric proportions (10%, 20%, 40%) of organic matter (OM), were determined using the HYPROP© method, which extends the traditional measurement range for soils. However, the high porosity of GR substrates resulted in tensiometer water column cavitation near -30kPa. Further studies with the same experimental substrates and OM ratios included both growth chamber studies to rigorously quantify the effects on plant growth and evapotranspiration and outdoor platform experiments to determine effects of OM content on stormwater retention. Growth chamber studies with Sedum kamptschaticum showed that increasing substrate OM increased plant root and shoot biomass. Consecutive periods of water stress showed no differences in evapotranspiration between planted substrate OM treatments levels, but greater water loss was noted from the planted treatments compared to unplanted controls (p<0.05). Substrate volumetric water content (VWC) during the stress periods reached 5% VWC for all planted treatments and all dry-down periods, highlighting differences in plant-available water between these and the laboratory results. While outdoor platform studies showed no effects of OM content on stormwater retention, increasing organic content increased plant canopy coverage (p<0.05). It is likely that differences in retention will be more defined over time as the system matures. Stormwater retention data represented the second growing season for the experimental platforms; given the effects of organic matter on plant growth, analysis of three- or even five-year retention will likely better predict the effects of organic matter on stormwater performance.

Joshua Yoshi Silverstein 

Parchment to Touchscreen: Landscape Journey and Experience for 21st Century Learning 

Experiences of landscape journey are informed and mitigated by modalities of place-based practices. Historically, documentation and transmission of landscape knowledge was limited to narratives of those with power and influence. Today, the democratization of power and decentralization of knowledge, particularly as affected by technology, are projected to affect powerful changes for our future. This project creates innovation in place-based learning through an interdisciplinary approach combining landscape design for outdoor learning environments with collaborative curriculum development. Educators from Gesher Jewish Day School in Fairfax, VA were involved in this collaboration that has yielded an exciting, fresh approach to engaging student relationships to landscape. Students connect to narratives of landscape journey and experience in Jewish tradition while engaging in guided personal explorations of place. In the process, new wisdom, the "Torah of Place," is generated, documented and transmitted through both traditional sense-of-place activities and pedagogies integrating modern mobile technology such as smartphones and tablets.

 Anna Elizabeth Wallis 

Local lettuce: heat tolerant romaine cultivars and vermicompost soil amendment to increase sustainability in the Mid-Atlantic 

Local production of lettuce in the Mid-Atlantic utilizing heat-tolerant romaine cultivars and vermicompost soil amendment has the potential to significantly increase sustainability of agriculture. Heat tolerant cultivars would facilitate season extension into the summer. Vermicompost, compost produced using earthworms, may increase yield and quality of lettuce crops. This research tested a system incorporating these two practices. Success was assessed on lettuce yield and quality of lettuce across three seasons (spring, summer, and fall) and food safety risk of vermicompost. Several of the heat tolerant cultivars showed marketing potential when grown in the summer. Vermicompost did not significantly increase lettuce performance, but trends indicate that it may help, especially at higher rates. No food safety risk was associated with tested materials.

Shoshanah Zahavah Haberman 

The Micro -Landscape Modular Urban Apartment Gardens 

 This thesis proposes affordable and adaptable modular balcony and patio gardens as a way to mitigate the increasing alienation between urban apartment renters and the land. These modules would adapt the concept of a garden to the compact reality of urban densification with an aim towards mitigation of urban stresses and improved well-being of apartment renters. Large-scale implementation would have environmental benefits, including stormwater capture and treatment, pollution control and heat island effect mitigation. This thesis design also has the potential to encourage renters, garden supply retailers, landscape professionals, architects and developers to incorporate private gardens, on a more extensive basis, into the fabric of the urban built environment. 

Travis Wierengo 

REVIVAL THROUGH RESILIENCE: Small Craft Harbor Design within a Coastal Urban Community 

Coastal communities along the Mid-Atlantic shoreline are facing difficult decisions moving forward into the 21st Century. The Rockaway Peninsula exemplifies many issues urban coastlines are facing. Environmental degradation, historic urban infill and development, a stagnant economy, and aging infrastructure, are only a few dilemmas communities along the Rockaway Peninsula are dealing with in the wake of the most current natural disaster that has left many questioning the future development of the area. This thesis explores what roles a Small Craft Harbor (SCH) could function as within an urban setting along the Atlantic coastline. The project will offer suggestions as to how programmatic elements within SCH development along the back bay shoreline of the Rockaway Peninsula, could serve to protect and enhance not only the human communities residing on the peninsula, but ecological systems fighting for survival within the back bay waters of the Jamaica Bay.

Amy Marin 

Operation Market Garden: Establishing a Sustainable Food System in West Baltimore's Poppleton Neighborhood 

Food deserts and food insecurity are public health concerns, associated with negative health outcomes for children and adults and connected to poverty, racial disparities, and other social inequalities. Urban agriculture offers one solution to the food accessibility issues in West Baltimore. Besides the initial purpose of food production, urban agriculture can play an important role in contributing at varying scales to the social interactions and economic viability of communities. These multifunctional landscapes can be used as design solutions for challenges posed by urban development. This thesis explores the roles that landscape architecture and urban agriculture can play in improving food environments for schools, families, and communities located in urban food deserts. This investigation examines urban agricultural planning strategies that address food accessibility issues and yield fresh produce, while also providing valuable public open space for community members. This project applies these strategies to the West Baltimore neighborhood of Poppleton to offer a critique of proposed urban agriculture solutions.

Paul Edward Jester 

Shifting Gears: Exploring Parametric Design to Renovate an Urban Waterfront 

A powerful tool currently being used by architects and planners, parametric design has yet to be embraced by landscape architects. Through research and design, this thesis seeks to answer two questions: what is parametric design and how can it benefit the field of landscape architecture? Looking at historical and present-day sources, the evolution of computer aided design has been drawn out leading to the emergence of parametric design. An explanation and analysis of parametric tools, including a series of case studies, has been conducted to show how these tools are presently being utilized by designers. Utilizing parametric methods and tools, a design proposal was created to renovate a waterfront site in Baltimore, MD that focused on highlighting the city history and promoting health for the local residents and inner harbor.

Elisabeth Jane Walker 

Exploring Socio-Cultural Dimensions of Sustainability. How Cultural and Social Factors Inform a Sustainable Redesign of Whitmore Park (Annapolis, MD). 

Even though sustainability is defined by four parameters - ecological, economic, social and cultural, sustainable design is essentially reduced to ecological and economic aspects (Nadenicek et al., 2000). That narrowed focus ignores those, on whom sustainable development depends on: people and their physical manifestation, culture. Sustainable design depends on both economic and ecological health, cultural vitality (Lister, 2007) and stewardship. When sustainable development does not encourage stewardship, it is prone to fail in the long term (Nassauer, 2011). This design-research thesis focuses on the socio-cultural aspects of sustainable design and the role of participatory engagement in identifying the social and cultural layers of Whitmore Park. It explores how cultural and social factors can inform a sustainable redesign of the neglected 0.7-acre Whitmore Park in Annapolis, MD. The project also helps the community to save the park´s existence through creating a common, sustainable long-term vision for it. In order to create that vision, the designer used various community engagement methods to reconnect the communities to their plaza, and to explore socio-cultural sustainable design approaches. The park´s new aesthetics, functions and programming are driven by the results of the community engagements, as well as the SITEs (Sustainable Sites Initiative) design recommendations. The citizens´ involvement, as well as the socio-culturally sensitive and aesthetically pleasing design will foster a sense of community, and pride, which are important conditions for stewardship and therefore, sustainable development.

Nancy Fruchter Britt 

Greenway as the Framework for Community Design on the Patapsco River Valley 

By the nature of their shared locality, greenway corridors and the communities along them share a unique set of socio-cultural and ecological resources that are rooted in the greenway's landscape form and character. When unified, greenways and surrounding communities foster a sense place that is deeply site specific. This thesis explores the unique characteristics of greenway landscapes, using them as a basis for formulating cohesive design criteria for creating vibrant greenway-adjacent communities. These criteria offer solutions for balancing growth and conservation strategies to guide community design within the framework of the greenway, achieve community and greenway sustainability, and support the integrity of the landscape. Using a site along Maryland's Patapsco River Valley, this thesis demonstrates how these criteria can work towards achieving an ideal community form where design highlights unique site features to create awareness of and support for the greenway context.

Adriana Mendoza 

Anacostia: Community As Form 

The essence of this thesis is to explore what form public art takes on in order to visualize Anacostia's community identity during the urban revitalization of the neighborhood. The current small and large-scale revitalization efforts by the City (Washington D.C.) are showing change in both the physical and social fabric of the community and neighborhood. As a predominantly African American community that has faced disinvestment and injustices--socially, economically, and politically--many residents are concerned that these City efforts will physically displace them, as well as the collective memory of the community. This thesis seeks to transform a vacant lot, slated for development, into a temporary, transient, multi-functional public art design for engaging the community in the process of exploration and expression of their community identity. Public art is used as a strategy to provide a platform for residents to effectively become present, visible and audible at a time when many residents feel as though they are not part of Anacostia's future.

Benjamin Conway 


Fusarium graminearum and Puccinia triticina are common wheat pathogens in the Mid-Atlantic region, causing Fusarium head blight (FHB) and leaf rust, respectively. Both diseases can cause serious yield losses in epidemic conditions and can be controlled by breeding resistant cultivars. MD01W233-06-1 is an adapted soft red winter wheat (SRWW) breeding line with previously uncharacterized "native" FHB resistance. SS8641 is an FHB-susceptible SRWW cultivar that has the leaf rust resistance gene Lr37 and an additional unidentified source of resistance. These parents were used to generate a doubled haploid mapping population to map their resistance to these diseases. Four FHB resistance quantitative trait loci (QTL) were mapped to chromosomes 3B (3 QTL) and 1A (1 QTL). Several QTL in SRWW have been mapped to these regions. Two leaf rust resistance QTL were mapped to chromosomes 2A, the same location as Lr37, and 5B, known to contain Lr18, previously unreported in either parent.

Cesar Samuel Herrera 


<italic>Cosmospora</italic> (in the broad sense; Nectriaceae, Hypocreales, Ascomycota) are fungi that parasitize other fungi, particularly fungi in the Xylariales (Ascomycota), or scale insects. Morphologically, these fungi are known for having one of the most simplest and smallest sexual fruiting bodies (<300 &#956;m) among the Nectriaceae. The sexual spores are generally warted. The majority of <italic>Cosmospora</italic> species have acremonium-like or fusarium-like asexual states. The name <italic>Cosmospora</italic> is derived from the ornamentation in the sexual spores (Gr. <italic>cosmos</italic> = ornamented + Gr. <italic>spora</italic> = spore). The main goals of this dissertation were to revise Cosmospora sensu stricto, and to determine the evolutionary relationship between <italic>Cosmospora</italic> species and their associated fungal hosts. Additionally, <italic>Corallomycetella</italic> (Nectriaceae, Hypocreales, Ascomycota), a lineage basal to <italic>Cosmospora</italic> sensu lato, was revised as well. Molecular and classical taxonomic tools were used to revise the genera. A genus was recognized if the clade met the following criteria: 1) the clade was well supported, 2) the clade was associated with a unique asexual state, and 3) the clade was ecologically different. A species was recognized if the clade met the following criteria: 1) the clade was well supported in the majority of single gene trees, 2) the clade was morphologically different, and/or 3) the clade was ecologically different in regards to host. <italic>Cosmospora</italic> species were observed to be highly host specific. Thus, host was recognized as an important character to delineate species, and the host specificity led us to hypothesize that <italic>Cosmospora</italic> species and their associated hosts were cospeciation (i.e., their association was not random). Two new genera, nine new combinations, and eleven new species were described in the taxonomic work included in this dissertation. A significant global congruence was determined between the <italic>Cosmospora</italic> and host phylogenies. However, host-switch events seemed more abundant in the early lineages of the host, while cospeciation events seemed more common in more recent lineages of the host. This phylogenetic signature is consistent with pseudocospeciation, but it could not be confirmed given that divergence estimates could not be estimated.

Catalina Salgado-Salazar 


The genus <italic>Thelonectria</italic> and related species with Cylindrocarpon-like anamorphs are a group of perithecial ascomycetes in the family <italic>Nectriaceae</italic> that occur as saprobes and in few cases as pathogens of hardwood trees, shrubs or other plant substrates. Despite of being a key component of forest ecosystems around the world, species relationships and distribution are largely unknown. The objectives of this study were to: 1) infer species level phylogenetic relationships of the genus <italic>Thelonectria</italic> and related species with Cylindrocarpon-like anamorphs with uncertain classification, testing monophyly of each one of the groups studied; 2) delimit taxa, establishing taxon circumscriptions and providing brief descriptions; 3) resolve nomenclatural issues by identifying redundantly used names and synonyms; 4) provide identification tools, specifically, diagnostic keys and molecular data that can be used further as molecular barcodes; 4) provide distribution data and to take the first steps into the identification of speciation patterns observed in these fungi. To achieve these goals, herbarium materials, as well as freshly collected material obtained from the field or from fungal repositories were compared using phylogenetic analyses of multiple loci, morphology and geographic distribution. This research resulted in the narrower circumscription of the genus <italic>Thelonectria</italic>, not to contain one of the most common species in the group, <italic>T. jungneri</italic>. According to the results of the phylogenetic analyses it was found <italic>T. jungner</italic>i is a segregating clade that needs to be recognized as a different genus. For the genus <italic>Thelonectria</italic>, a total of 31 new species were described, and three new genera, closely related to <italic>Thelonectria</italic> were created to accommodate the diversity of other species with Cylindrocarpon-like anamorphs: <italic>Cinnamonectria</italic> gen nov. with <italic>C. cinnamomea</italic> as type taxon, <italic>Macronectria</italic> gen. nov. with <italic>M. jungneri</italic> as type taxon, and <italic>Tumenectria</italic> gen. nov. with <italic>T. laetidisca</italic> as type taxon. Species in this group of fungi present extensive morphological conservationism, representing a challenge for species identification without the use of molecular techniques, however offering a great opportunity to explore mechanisms of speciation and evolutionary diversification.


Clark DeLong 


The evaluation of plant species for use in green roof systems is an important step in providing recommendations to the industry. In this study we investigated the ability of five species to grow and survive on a green roof in the Mid-Atlantic, and how they contributed to the performance of a green roof system. One species, Tradescantia ohiensis was found to retain more storm water than other species and an unplanted control. Three of the plants evaluated were found to reduce substrate temperatures when compared to unplanted controls during the summer months. One species, Chielanthes lanosa, was unable to survive the summer. While another, Asclepias verticillata, lost biomass over the study. Indicating both are unsuitable for use on green roofs in the Mid-Atlantic. The other species: Sedum album, Sedum kamtschaticum and Tradescantia ohiensis all survived and exhibited a positive growth rate.

Megan Elizabeth McConnell 

Distribution and involvement of Phytophthora cinnamomi in white oak (Quercus alba) decline in mid-Atlantic United States forests 

The association of <italic>Phytophthora cinnamomi</italic> with declining white oaks was studied at 102 sites in mid-Atlantic oak forests. Seven <italic>Phytophthora</italic> species were isolated from 44 sites. <italic>P. cinnamomi</italic> was restricted to USDA plant hardiness zones six and seven, and <italic>P. cinnamomi</italic> propagules in soil were significantly higher in zone seven than in zone six. When white oak fine root lengths of infected and <italic>Phytophthora</italic>-free trees were compared, infected trees had significantly lower fine root amounts. However, infected trees in zone seven had more fine roots. Little difference in pathogenicity between 32 <italic>P. cinnamomi</italic> isolates was found during white oak seedling stem inoculations. Fine root lengths of inoculated white and red oak seedlings decreased most during the spring. Propagule density in soilless potting media decreased with increasing temperature, except at 8°C and 16°C. These studies demonstrated that the impact, survival and spread of <italic>P. cinnamomi</italic> are strongly linked to environmental conditions and host species.

Qingmel Guan 


Abiotic stresses, such as temperature extremes and salinity adversely affect plant productivity and distribution worldwide. Resistant or susceptible to stresses is a complex trait because more than one stress may occur simultaneously, for example, salinity is accompanied with ion toxicity and water deficit. To survive in a fixed environment, plants have to adjust their metabolisms and developmental programs to adapt to the stress or acclimate to the transitory stress. The responses of plants to different abiotic stresses are extremely complex, involving stress perception, signaling transduction, and response induction. We took a forward genetic analysis approach and identified three novel proteins in the reference plant Arabidopsis thaliana, Regulator of CBF Gene Expression 1 (RCF1), Regulator of CBF Gene Expression 3 (RCF3), and Short Root in Salt Medium 3 (RSA3), which are critical for plant tolerance to cold, heat and salinity, respectively. RCF1 is a cold-inducible DEAD box RNA helicase protein which is localized in the nucleus. RCF1 is a positive regulator for chilling and freezing tolerance. RCF1 functions to maintain proper splicing of pre-mRNAs because many cold-responsive genes are mis-spliced in rcf1-1 mutant plants under cold stress. RCF3 encodes a KH-domain containing putative RNA-binding protein. RCF3 is a negative regulator of most heat stress transcription factors (HSFs). Consistent with the overall increased accumulation of heat-responsive genes, the rcf3 mutants are heat-tolerant. RSA3, a xylogluscan galactosyltransferase, is essential for salt stress tolerance. rsa3-1 mutant plants are hypersensitive to NaCl and LiCl but not to CsCl or to general osmotic stress. RSA3 controls expression of many genes including genes encoding proteins for reactive oxygen species (ROS) detoxification under salt stress. RSA3 functions to maintaining the proper organization of actin microfilaments in order to minimize damage caused by excessive ROS. miRNAs play important regulatory roles in plants by targeting messenger RNAs (mRNAs) for cleavage or translational repression. We determined role of the heat-inducible miR398 in plant heat stress tolerance. Our results suggest that plants use a previously unrecognized strategy to achieve thermotolerance, especially for the protection of reproductive tissues. This strategy involves the down-regulation of two copper/zinc superoxide dismutase (CSDs) and their copper chaperone CCS through the heat-inducible miR398.

Olyssa Starry 

The comparative effects of three Sedum species on green roof stormwater retention 

Green roofs are typically dominated by Sedum species because they can tolerate hot, xeric environments. However, due to their high water use efficiency, some have questioned the selection of these species for stormwater management. We investigated (1) how three common Sedum species contribute to overall stormwater retention efficiency by green roofs in the mid-Atlantic region, and (2) whether species-specific differences in water use could be explained by morphological and physiological characteristics. Water use and CO<sub>2</sub> exchange were continuously monitored in growth chamber studies under increasing drought stress for <italic>S. album</italic>, and <italic> S. kamtschaticum</italic>, two species known to variably cycle between CAM and C3 metabolisms. Under fall temperature conditions, <italic> S. kamtschaticum</italic> had gas exchange rates akin to C3 photosynthesis and used 35% more water compared to <italic>S. album</italic>. Interestingly, <italic>S. album</italic> conserved water and had malic acid accumulation confirming CAM metabolism for the duration of the experiment, even under well-watered conditions. In field studies, sixteen replicate green roof platforms (n=4 per species) were planted with <italic>S. album</italic>, <italic>S. kamtschaticum</italic>, <italic>S. sexangulare</italic>, or left unplanted during summer 2010. The platforms were monitored intensively for canopy growth, leaf area, root biomass, substrate moisture and runoff for two years (2011 and 2012). Plant treatment effects on stormwater runoff were significant, but most discernible for small and intermediate-sized rainfall events less than 62.5mm. The two species with the greatest stormwater retention efficiencies, <italic>S. kamtschaticum</italic>and <italic>S. sexangulare</italic>, also had the highest rates of evapotranspiration (ET), and higher ET rates resulted in less total runoff. Because evapotranspiration was identified as important for predicting performance by plants in the field study, I investigated how ET data from this study, combined with environmental data collected from a weather station at the study site, could be used to improve the application of the FAO56 Penman-Monteith evapotranspiration equations to green roofs. The incorporation of specific seasonal crop coefficients were found to improve correlations between predicted and measured rates of ET and these coefficients were related to plant characteristics. The refinement of ET equations can lead to more accurate hydrologic models of green roofs and design and management tools.

Sarah C. Ashmun 

Healing Invisible Wounds: Landscapes for Wounded Warriors Suffering from Posttraumatic Stress Disorder (PTSD) 

Characterized by pervasive symptoms of intrusion, numbing, and hyperarousal, coping with PTSD can be a tenacious and lifelong challenge for sufferers (Cahill and Foa 2010). Given the recent surge of war veterans resulting from Operations Enduring and Iraqi Freedom with a high prevalence of PTSD, landscapes may provide a free and accessible means for veterans to successfully cope with their PTSD symptoms and seek treatment. The intention of this project is to merge holistic therapies for PTSD with successful landscapes for trauma patients into the creation of adaptable design principles. Guiding Principles for PTSD will be incorporated into the design of a Healing Woodland for wounded warriors at the Walter Reed National Military Medical Center in Bethesda, Maryland, while also providing potential solutions for other sites aiming to incorporate holistic therapies for PTSD into the landscape.

Matthew Busa 

Designing for the Shrinking City: Re-imagining Burke Lakefront Airport in Cleveland, OH 

Like many post-industrial cities in the Midwestern United States, Cleveland is shrinking. A decline in its manufacturing-based economy in the late 20th century has led to unemployment and outmigration, eroding the quality of life and economic stability of inner city neighborhoods. Traditional planning strategies that rely heavily on growth as a means of addressing shrinking city problems have proven to be somewhat ineffective. This thesis explores an alternative planning approach suggesting that Cleveland might successfully shrink into an archipelago of small, sustainable neighborhood islands while failed neighborhoods would be converted to productive "green belts". This project applies this approach to the site of an under-utilized municipal airport, proposing a new design that enhances the social, economic, and environmental sustainability of Downtown Cleveland. Specifically, the design solution promotes transit-oriented development, connects existing neighborhoods to the waterfront, cleans polluted water, and re-uses dredge material to create a recreational and ecological landscape.

 Emilie Carroll Carter 

Designing for Interpretive Signage: Best Practices for Increasing Attraction Power 

Interpretive signage, murals, and art installations are an important element of passive outdoor education for those who do not have formal education or knowledge about how landscapes work. The inclusion of passive education in projects has become increasingly necessary as new types of green infrastructures such as rain gardens, bioswales, and floating wetlands, are introduced to the landscape. Landscape architects can contribute to educational efforts by including interpretive signage on a site. While this practice is being implemented among many sites around the United States, it is unclear how effective these installations are in educating the public - specifically adults. This thesis project takes an in-depth look at the effectiveness of interpretive signage located around low-impact design elements and proposes a set of best practices for designing sites with interpretive signage. To support the best practices, data is being collected at two sites with methods that include surveying site occupants, field observation of occupant interactions with signage, and interviews with project designers. Initial data analysis from the pilot study shows that interpretive signage does positively affect people's views on environmentally sensitive design, but a variety of factors such as signage location and visibility of installation can affect the percentage of people who read signage.

Mingyu Cui 


This design-research thesis suggests that the improvement of campus roadway facilities using Complete Streets principle and practices can enhance the overall pedestrian experience. Campus Drive, one of the main arterials in the College Park campus of the University of Maryland, will be used as a case study. Heavily used by a variety of users, often conflicting with one another, University of Maryland Campus Drive would benefit from a major planning and design amelioration to meet the increasing demands of serving as a university main street. The goal of this thesis project is to prioritize the benefits for pedestrians in the right-of-way and improve the pedestrian experience on campus. This goal also responds to the recent Facilities Master Plan vision of building a more walkable campus. The goal of this design-research thesis will be achieved focusing on four aspects. First, design and plans will discourage cut-through driving to reduce vehicular traffic volume on Campus Drive in order to reduce pedestrian and vehicle conflicts. Second, plans and designs will clarify cyclists' use of the right-of-way and create a built environment that will reduce and hopefully eliminate current riding on pedestrian sidewalk. Third, the case study seeks to improve public transit facilities on Campus Drive to better serve users of which the majorities travel as pedestrians on campus. Finally, the case study seeks to improve pedestrian facilities to enhance pedestrian connectivity, accessibility, and overall experience on University of Maryland Campus Drive. Campus Drive roadway facilities will be inventoried. Roadway segments typologies will be identified and classified. A toolkit, road improvement design interventions, will be developed based on this classification. An improved master plan will be developed utilizing the toolkit while considering the specific site context around specific segments and the overall functions carried by Campus Drive as a campus main street. Detailed plans and designs will be developed for focus areas that demonstrate the goals and objectives. The outcome of the design-research thesis project is expected to serve as an example of implementing Complete Streets principles and practices in urban commuter university campuses, where transportation needs and institutional functions interact with each other.

Nicholas Alan Patrick 

Experiencing Temporary Artscapes 

The focus of this thesis is on temporary artscapes - public installations that are originally-creative and intentionally-temporary in some way. A temporary art installation has the ability to quickly and clearly transform a place, increase our understanding and awareness of a particular site, and redefine and highlight the importance of public space. This design-research thesis proposes that temporary artscapes have the capacity to significantly alter the experience of a landscape. Through the investigation and evaluation of the theories, intentions and working methods of the artists, landscape architects, and architects involved in recent projects, this thesis explores the value of temporary artscapes in landscape-design. Two key research investigations assist this investigation. Designing the Experience explores the artistic process of designing a temporary installation, through the collaborative designing and building of a temporary art installation with a sixth-grade class at the British School of Washington. Experiencing the Design explores the experience of a temporary art installation from the perspective of the public audience, through the surveying of people during a temporary art installation in a prominent public space at the University of Maryland. The outcomes of the investigation and two research investigations determine my strategy in choosing a site within the University of Maryland campus in which to design and test a conceptual temporary artscape.

Erica Marie Thum 

Light in the Landscape 

This design-research thesis proposes the redesign of Tide Lock Park in Alexandria, Virginia as an exploration of light. By researching the cultural history of artificial lighting as well as the sculptural use of light as art, this thesis seeks to distinguish lighting design that goes beyond functional and safety concerns to include design that honors the human relationship to darkness, as well as the artistic and emotive qualities of lighting. To accomplish these goals, this thesis proposes a landscape design for Tide Lock Park which meets the City of Alexandria's objectives as described in the Waterfront Small Area Plan. The design includes three distinctive areas of light, providing visitors the opportunity to engage the night in multiple ways.

Laura M. Kendrick 

The Purposeful Edge: Designing for Wildlife Along the Anacostia River 

As urbanization increases, many cities will reassess their land use policies and practices to establish a balance between densification and ecological sustainability. Creating and improving urban wildlife habitat can increase biodiversity and provide places for people to experience native vegetation and animals. Among the inspiring collection of culturally significant places, Washington, DC has many small reserve parks. For wildlife habitat to be sufficient, larger tracts are often needed. This thesis project capitalizes on one such expanse along the Anacostia River by proposing the area surrounding Robert F. Kennedy stadium and its parking lots become places where habitat is integrated into the urban fabric. Integration means creating spaces where humans and wildlife coexist, each enhancing the lives of the other by their interactions. Healthy ecosystems are a piece of the sustainability puzzle, and the future of the world's cities must include the application of ecological knowledge in designing urban spaces.

Sarah Watling 


Swaziland's Ngwenya Mines, the oldest known mine in the world, has been a source of ochre for cultural use for over 43,000 years. Until the 20th Century, extraction at Ngwenya Mine left an imperceptible mark on the landscape until industrial technology enabled new mining practices that have dramatically and irrevocably altered this landscape. The intent of this thesis is to further the development of mine reclamation models and ultimately benefit similar sites around the world. By building on current mine reclamation strategies where Land Art is a mediator between ecology and industry, this thesis focuses on the important story Ngwenya Mine can tell. With no intervention, the conclusion will be an untreated landscape with limited potential. With creative design responses, a story of cultural and ecological integrity can persist into the future.

Emily Ann Pettengill 


Nutrient remobilization and storage allow plants to direct resources toward growth, maintenance and reproduction and redirect nutrients in response to environmental conditions or stresses. Particularly for perennial plants, these capabilities are critical to surviving periods of unfavorable growth such as winter and nutrient limited environments. In <italic>Populus</italic>, bark storage proteins (BSPs) have a dominant role in seasonal storage, and proteins related to BSPs, known as nucleoside phosphorylase-like (NP-like) proteins, can also participate in short-term storage. This research presents a comprehensive examination of the NP-like gene family by characterizing their expression, exploring evolutionary relationships within the plant kingdom and investigating metabolic regulation. I also developed and tested a set of qPCR reference genes to use for data normalization in two <italic>Populus</italic> species and four tissue-types. Lastly, transgenic trees were created to investigate the developmental or physiological functions of altered levels of BSP. Experiments characterizing the spatial and temporal expression of NP-like genes implicated a functional role for all members. Those results also support the phylogenetic analyses demonstrating the expansion of the gene family, which may have occurred through subfunctionalization. I also examined the regulation of carbon (C) and nitrogen (N) metabolites on the NP-like gene family expression and observed that amino acids, N compounds and gamma-aminobutyric acid (GABA) treatments modulate expression and likely have a role in regulatory pathways. By investigating transgenic trees with altered BSP levels, I present preliminary evidence that BSPs may have a role in nutrient signaling capable of modulating photosynthesis in young leaves. The results of this work deepen our understanding of nutrient remobilization and storage in <italic>Populus</italic> on regulatory, evolutionary and functional levels. Practically, the results can advance efforts to increase N use efficiency for sustainable biomass increases in <italic>Populus</italic> for use in agro-forestry, as biofuel feedstock, in phytoremediation and for carbon sequestration.

Wenjie Li


In 2010, the United States Environmental Protection Agency (EPA) determined the Total Maximum Daily Load (TMDL), a "pollution diet", for the Chesapeake Bay watershed for six states (New York, Pennsylvania, Delaware, Maryland, West Virginia, Virginia) and the District of Columbia. The EPA required responsible agencies to develop statewide Phase I Watershed Implementation Plans (WIPs) to support the implementation for TMDLs. Previous planning efforts included the development of Subwatershed Action Plans (SWAPs), which provided a baseline of conditions, proposed tools for achieving TMDL reductions and visions for the subwatersheds. In 2012, the Phase II WIP process was developed to refine Phase I plans at the county level, including more local details about a variety of green infrastructure interventions to optimize nutrient and sediment load reductions. While green roofs were considered an important tool in the SWAP plans, they were not included in Prince George's County's Phase II WIP plans. Recently, Prince George's County has implemented a new green roof incentive policy. In light of this new policy, this research explores how green roofs might contribute to reducing TMDLs. The research uses Brier's Mill Run Subwatershed as a case study to demonstrate the benefits of both the incentives and the green roof as a tool in the SWAP plan. The objective of this research is first to document the specific role of green roofs in stormwater management in Brier's Mill Run Subwatershed. Secondly, the thesis provides three metrics to measure and compare the stormwater management benefits of each proposed institutional green roof in the research site. The third goal is to use a scenario approach to achieve school green roofs benefits that contribute to the stormwater management goals of the subwatershed.

Risa Dessel Abraham 

Revealing Risk & Redefining Development: Exploring Hurricane Impact on St. Croix, USVI 

This thesis explores the direct and indirect role of landscape architecture in disaster risk reduction specifically focusing on designing and managing natural resources such as sun, wind and water as well as allocating infrastructure to improve the power and transportation system on the public, private and regulatory levels that can prove to endure the impact of a hurricane and promote a "culture of prevention." Every year a significant amount of damage is cause by natural disasters throughout the whole world. This highlighted the importance of mitigating the adverse impacts of disasters through the process of disaster risk reduction. The architecture, landscape architecture and urban design disciplines and the construction industry have a strong relationship with disaster management and therefore provide a high need in identifying how landscape architecture can contribute towards disaster risk reduction. This thesis focuses on the role of the design and construction industry, specifically the landscape architecture profession, in disaster risk reduction. A two-step approach was formalized to develop an understanding and to produce a design proposal based on the practice and theories of landscape architecture. The first step explores the definition of disasters and risk and provides a comprehensive literature review on disaster mitigation. The second step includes the systematic development and application of these policies, strategies and practices to limit or avoid the effects of hazards in the form of a three-tiered detailed design and mitigation plan. The findings from both steps will be applied to re-design the town of Christiansted, St. Croix, in the United States Virgin Islands.

Patrick Howard Watkins 

Nitrogen Management in Corn: Influences of Urea Ammonium Nitrate (UAN) Applications With and Without Nitrogen Stabilizer Products. 

Corn (Zea mays, L.) is a major crop produced in the nutrient sensitive Mid-Atlantic region. Nitrogen use efficiency (NUE) for corn is considered sub-optimal and farmers in the region use a number of best management practices (BMPs) to improve corn NUE. Two sidedress application methods (surface banding and sub-surface injection) and four commercially available nitrogen stabilizer products (`Agrotain', `Agrotain Plus', `Instinct', `Nutrisphere-N') were investigated during 2009-2011 over three N fertilizer rates at nine total locations. Headspace ammonia accumulation (post-sidedress) was indexed to the surface applied UAN treatment and resulted in application method and stabilizer products having a significant effect for headspace ammonia accumulations. Post-harvest inorganic soil nitrogen was not affected by application method or stabilizer products. Yield was not significantly affected by application method or stabilizer products but was affected by N rate. Total plant N concentration was not significantly affected by application method or stabilizer products.

Jennifer Carol Himmelstein 


The cover crop Vicia villosa suppresses Fusarium wilt of watermelon but the mechanisms of disease suppression are unknown. Possible mechanisms were examined in field, greenhouse, and in vitro experiments. The effects of cover crop treatments (V. villosa, Trifolium incarnatum, Secale cereale, Brassica juncea) and the biocontrol treatment Actinovate (Streptomyces lydicus WYEC 108) on Fusarium wilt of watermelon and its causal pathogen, Fusarium oxysporum f. sp. niveum (FON) were evaluated. In four of five field experiments there were significant elevations in soil microbial respiration. Arbuscular mycorrhizal colonization of watermelon roots following cover crop amendments of V. villosa and T. incarnatum, were significantly higher compared to bare ground. The elevation in respiration was significantly positively correlated with disease suppression of Fusarium wilt induced by V. villosa and T. incarnatum (both cover crops reduced Fusarium wilt as much as 21%). In greenhouse experiments using infested field soil, Fusarium wilt suppression was observed in pots amended with V. villosa and T. incarnatum. However, there was an increase in Fusarium wilt of watermelon in pots that were amended with V. villosa and T. incarnatum which were also inoculated with FON when compared to plants in nonamended, inoculated pots. These leguminous cover crops may have served as a nutrient source for the pathogen. In addition, in vitro growth experiments showed that media amended with V. villosa leachate significantly stimulated the in vitro growth rates of FON and Trichoderma harzianum compared to nonamended plates. It was hypothesized that V. villosa stimulation of nonpathogenic F. oxysporum spp., which provides cross protection against FON, may have contributed to the wilt suppression. Cover crop leachate amendments did not significantly influence colony forming units of S. lydicus. In both field and greenhouse trials Actinovate applications either had little or no effect on Fusarium wilt of watermelon. However, S. lydicus significantly inhibited in vitro growth of FON. These studies demonstrate that both general and specific disease suppression play a role in V. villosa suppression of Fusarium wilt of watermelon and that T. incarnatum is a viable alternative biocontrol.


Carol Dianne Allen 


ABSTRACT Title of Thesis: TRANSMISSION OF <italic>CYMBIDIUM MOSAIC VIRUS</italic> IN ONCIDIUM ORCHIDS BY <italic>PERIPLANETA AUSTRALASIAE</italic> Carol Dianne Allen, Master of Science. 2012 Thesis Directed by: Gary Coleman, Ph.D. Department of Plant Science and Landscape Architecture <italic>Cymbidium mosaic virus</italic> is the most common disease in orchids infecting a large number of cultivated orchids found in all phases of the industry and around the world. Its transmission occurs through contact by contaminated cutting tools, human hands, or water. Although insects known to transmit plant viruses have been exposed to orchid viruses, none have been found to successfully transmit <italic>Cymbidium mosaic virus</italic>. <italic>Periplaneta australasiae</italic>, the Australian cockroach, is a common greenhouse pest that is known to feed on orchid plants. In controlled conditions Australian cockroaches were given inoculation access through feeding activity on known CymMV positive orchid plants and then allowed to feed on virus free plants. The virus free plants were isolated from subsequent insect exposure and after a period of time samples from the feeding damage sites were analyzed for the presence of virus RNA through nested and hemi-nested PCR techniques. A statistically significant number of samples were positive demonstrating that with high population numbers and long term exposure, virus transmission is possible.

Michael Warren Lloyd 

Genetic consequences of habitat fragmentation and restoration 

The objective my dissertation was to assess the effects of habitat loss and fragmentation on genetic diversity and landscape connectivity. I focused on <italic>Vallisneria americana</italic> Michx. (Hydrocharitaceae), a submersed aquatic plant species found in the Chesapeake Bay. <italic>Vallisneria americana</italic> has undergone dramatic changes in abundance and distribution throughout its range and has been targeted for restoration, which makes it ideal for examining the effects habitat loss and fragmentation. I examined the naturally occurring genetic diversity across the Chesapeake Bay and its major tributaries. Sites were genetically diverse, but had a range of genotypic diversities. There were four genetic regions, corresponding with geographic regions in the Bay. <italic>Vallisneria americana</italic> has been the target of restoration, and restoration techniques could be influencing genetic diversity and potentially lowering overall success. I examined various restoration techniques across eight restoration sites, and found that technique did not greatly influence genetic diversity. However, small population size, significant inbreeding coefficients, and low overlap of allele composition among sites provide cause for concern. Measures of functional and potential connectivity provide insights into the degree of contemporary gene flow occurring across a landscape. Pollen dispersal distance was measured using indirect paternity analysis, and is spatially restricted to only a few meters. Dispersal at this scale imposes small genetic neighborhoods within sites, evidenced by high seed relatedness within mothers. I used a graph theoretic approach to examine the distribution and potential connectivity of historic and current patches of <italic>V. americana</italic>. There was a high turnover in the distribution of patches, and connectivity varied through time, but even if all habitat were occupied, increases in overall network connectivity would not necessarily be observed. I developed an individual based model that I used to test the ability of measures of genetic differentiation to detect changes in landscape connectivity. Genetic differentiation measures became significant after two generations, but the magnitude of change in each was small in all cases and extremely small when population sizes are greater than 100 individuals. These results suggest that genetic differentiation measures alone are inadequate to rapidly detect changes in connectivity.

 David Emmanuel Ruppert 

Redox and Soil Manipulation Effects on Ditch Soil Phosphorus Processing 

Ditches increase the connectivity of landscapes to open water systems, potentially facilitating the degradation of downstream waterways. A treatment and an observational experiment were conducted to identify processes behind phosphorus (P) cycling in ditch soils. If the ditch had not undergone recent dredging soils were observed in the treatment experiment to release P to surface water whether the soil system was iron (Fe)-oxidizing or Fe-reducing. Also in the treatment experiment, Fe was released to surface water in appreciable amounts only if the soil system was Fe-reducing. From the observational experiment P release due to mineralization was inferred due to a positive trend with temperature. Also in the observational experiment Fe-reducing conditions were weakly correlated with diminished P concentrations in the ditch water. It was inferred that emergent Fe(II) released from within the soil through reductive dissolution captures P from ditch surface water upon oxidation. In the treatment experiment dredging and saturated conditions resulted in similar effluent P concentrations as drained soils that were undredged. This may explain a lack of dredging effect that was observed in the field.

Jennifer Zoe Clarkwest


This interdisciplinary research-design thesis explores the role of resident engagement in developing a design criteria for urban stormwater runoff design solutions, urban greening, and activating public spaces in the urbanized McElderry Park neighborhood of Baltimore. Drawing upon stakeholder and resident interviews, community workshops, resident working groups, and site observations and analysis the designer developed design criteria for site interventions as well as neighborhood-wide programming elements. Residents identify jobs, safety and health as primary concerns. Beyond harvesting stormwater, site interventions must provide safety, education, entrepreneurial opportunities, exercise, etc. Building on community input, the design interventions proposed by the designer are site specific, but the intervention types are readily adaptable. The overall design process and programming strategies apply to a variety of urban sites. Given the amount of stormwater managed by the interventions, the potential jobs created by the interventions, and other benefits provided to residents, the model merits field testing at the neighborhood scale.

Kimberly Jean Moyer 

Wildness as Infrastructure 

An interesting line of tension happens when wildness is physically juxtaposed with order. This tension is an emblematic feature of the urban wildscape. This research/design thesis explores ways to inject qualities of wildness into the urban environment where order, functionality, and safety are a necessary part of the landscape. The exploration is primarily focused on aesthetics; the full engagement of the senses in the perception of the environment. Nevertheless, the sustainability of urban wildscapes has important implications for its survivability. With appropriate research and design, a degraded urban landscape can be transformed into a minimal maintenance wildscape. The goal of this project is to identify design parameters and apply them to a specific place: Baltimore's "Highway to Nowhere" with designed acts of intervention and a restrained approach to maintenance. The intent of these interventions is to encourage a predictable succession of urban wildlife habitats with varying levels of human presence.

Chris H. Myers


This paper will discuss design elements to enhance pollinator and avian diversity on a green roof in the District of Columbia. Biodiversity trends on green roofs in Canada, the United Kingdom, Switzerland, and the United States are discussed. Focusing on North America, reconciliation ecology is explored through the use of case studies. The design process for designing a green roof is divided into three parts: identifying program goals, site analysis, and design concept. Design guidelines are extrapolated from conservation literature for the creation of green roofs that support pollinator and avian habitat. These "bioroofs" will be draped over the United States Coast Guard Headquarters building which will serve as a template for creating a green roof to target the least tern, the killdeer, the butterfly and the bee, in the District of Columbia.

Rosamaria Mora Montenegro 


"Puertas", translated as portals or gateways, give residents and visitors the first visual images of the city. Their importance depends in the way they connect two areas, as well as in the way they give identity to the city as a whole. With the expansion of the city, the Historic District of Panama (Casco Antiguo) lost part of its defensive wall and its two original city entrances: Puerta de Tierra (Land Gateway) and Puerta de Mar (Water Gateway).When these elements were destroyed, the city lost part of its physical boundaries and part of its identity as a fortified colonial settlement. This thesis is a historical and design investigation into the role of city entrances and how their interpretation in Casco Antiguo can improve the visitor's experience. The reinterpretation of these entrances will also mark the boundaries of the Historic District that function as meaningful links between Casco Antiguo and its surrounding areas.

Kroy Anne Kreiseder 

Addressing New Stormwater Policies in the Redesign of the National Grove of State Trees at the United States National Arboretum 

The National Grove of State Trees at the United States National Arboretum is in need of redesign to meet ecological and social needs. The Grove serves as a scientific and cultural landscape and can be repurposed to serve the public as an ecological demonstration for contemporary environmental issues. In an intensive effort to clean up the local rivers of the District of Columbia and the Chesapeake Bay, the two agencies of the District Department of the Environment and DC Water have enacted stormwater runoff fees, based on impervious surface fees, on all property owners located in the District of Columbia. The redesign of the Grove is compounded by the Arboretum's need to add more parking to the area where the Grove is currently located. The objective of this thesis is to reimagine the design and interpretation of the Grove as well as address the impervious area charge assessments.

Allison Palmer Jensen 


The artful management of stormwater has a capability to create educational arenas by combining environmentally sensitive rainwater design with education. School settings provide great opportunities for integrating on-site stormwater treatment into many aspects of the curriculum from the sciences to the arts. Presently, urban settings have new initiatives for creating green schools, which covers all levels of sustainability for the campus. This research project focuses on the development of stormwater and water-related designs for Georgetown Visitation Preparatory School in Georgetown, Washington DC. The main research is an assessment of the school's existing stormwater usage and runoff and also evaluating possibilities for new stormwater management techniques to be a supplement to curriculum.

Michael Allen Boeck 

Reimagining the Cambridge Shoreline: Encouraging Implementation of Sustainable Shoreline Erosion Controls in Cambridge, MD 

Erosion in the Chesapeake Bay area occurs naturally and unnaturally. It is a concern for property owners, environmentalists, and communities. New legislation in Maryland specifies "living shoreline" as the preferred type of erosion control. Long-term success of the legislation depends on public support. Choosing to restore degraded or structural shorelines is an expensive undertaking and arguments that rely on environmental benefits alone are insufficient. The key is to develop, design, and promote erosion control devices that meet property owner and community goals. This research-design thesis asks the following question: As `living shorelines' become the preferred method of shoreline erosion control in the Chesapeake Bay, how can these shorelines be designed to meet the goals of property owners and residents, while being environmentally sensitive? The author argues that shoreline designers must integrate human dimensions research as well as scientific research into their designs in order to encourage widespread implementation.

Matthew J. Sickle 

Nomadic Memorial: Dynamic Landscapes of Commemoration for the Civilian Public Service 

This design-research thesis suggests the creation of a memorial commemorating the Civilian Public Service (CPS), a World War II era program of alternative service for conscientious objectors. Through an exploration of memorial culture, the thesis seeks to distinguish the commemoration of nonviolence from the commemoration of war and to propose a memorial that inspires its visitors to consider nonviolence and conscientious objection as positive aspects of American culture. To accomplish these goals, a memorial composed of modular commemorative elements was designed. Rearranging this kit of parts in combination with a new group of locally appropriate trees, the memorial will relocate to a different American city each year and return to Washington, D.C. every four years. With the growth of a new grove of trees and its donation to the neighborhood the memorial inhabits, the latter will draw attention to the history and the variety of services performed by the CPS.

Julia Mae Harshman 

Evaluation of Raspberry (Rubus sp.) Genotypes for Postharvest Quality and Resistance to Botrytis cinerea 

Raspberries are a delicate, high value specialty crop with an extremely short shelf life. This is exacerbated by their susceptibility to postharvest decay caused by <italic>Botrytis cinerea</italic>. Of the three commercially available species, red raspberry (<italic>Rubus idaeus</italic> L.) is the most widely grown. Yellow (<italic>R. idaeus</italic> L.), black (<italic>R. occidentalis</italic> L.) and purple raspberries (<italic>R. × neglectus</italic> Peck.) are mainly available from direct marketers. The quality and storageability of 17 cultivars was examined weekly from June to September during two growing seasons. Storage life was assessed weekly, while firmness, color, respiration and ethylene evolution rates were measured in select harvests. Black and purple raspberries outperformed red and yellow cultivars in their ability to resist <italic>B. cinerea</italic> colonization. Black raspberries also had the lowest ethylene evolution rates and incidence of decay. This information will be useful to raspberry breeding programs by identifying physiological characteristics that are correlated with greater resistance to <italic>B. cinerea</italic>.

Joseph Ikley 

The utility of saflufenacil on glyphosate-resistant horseweed and its effect on select soybean varieties 

Glyphosate-resistant (GR) horseweed [Conyza canadensis (L.) Cronq.] is a major weed in soybean [Glycine max (L.) Merr.] production across the United States. Saflufenacil is a new herbicide labeled for control of GR horseweed in soybean. Due to sensitivity concerns, applications are restricted to 30 days preplant (DPP) on coarse-textured soils with less than 2% organic matter (OM). The utility of saflufenacil tank-mixes on GR and glyphosate-susceptible (GS) horseweed was evaluated in the greenhouse. Saflufenacil at 25 g ai ha-1 tank-mixed with glyphosate at 874 g ae ha-1 resulted in better control of GR and GS horseweed than either product applied alone. In field studies, saflufenacil tank-mixes were applied 30, 15, and 0 DPP to soybean on a coarse-textured and a medium-textured soil. Saflufenacil applied at 50 g ai ha-1 caused a 15-30% reduction to yield and yield components when applied 15 and 0 DPP on the coarse-textured soil

 Romina Gazis 


The main objectives of this dissertation project were to characterize and compare the fungal endophytic communities associated with rubber trees (Hevea brasiliensis) distributed in wild habitats and under plantations. This study recovered an extensive number of isolates (more than 2,500) from a large sample size (190 individual trees) distributed in diverse regions (various locations in Peru, Cameroon, and Mexico). Molecular and classic taxonomic tools were used to identify, quantify, describe, and compare the diversity of the different assemblages. Innovative phylogenetic analyses for species delimitation were superimposed with ecological data to recognize operational taxonomic units (OTUs) or "putative species" within commonly found species complexes, helping in the detection of meaningful differences between tree populations. Sapwood and leaf fragments showed high infection frequency, but sapwood was inhabited by a significantly higher number of species. More than 700 OTUs were recovered, supporting the hypothesis that tropical fungal endophytes are highly diverse. Furthermore, this study shows that not only leaf tissue can harbor a high diversity of endophytes, but also that sapwood can contain an even more diverse assemblage. Wild and managed habitats presented high species richness of comparable complexity (phylogenetic diversity). Nevertheless, main differences were found in the assemblage's taxonomic composition and frequency of specific strains. Trees growing within their native range were dominated by strains belonging to Trichoderma and even though they were also present in managed trees, plantations trees were dominated by strains of Colletotrichum. Species of Trichoderma are known for their biocontrol properties, whereas species of Colletotrichum have been always associated with plant disease.

 Joyce Kelley 

Redefining the ORILLA: community awareness at the water's edge in Baltimore 

This thesis proposes a redesign of a waterfront park in South Baltimore, Maryland. Middle Branch Park, located one mile south of Baltimore's Inner Harbor, offers a unique opportunity to restore a degraded shoreline in the context of watershed stewardship. This thesis strives to reestablish Middle Branch as a functional critical buffer within the urban fabric of Baltimore city by utilizing shoreline restoration techniques, stormwater management and floating wetlands. The issues of water quality within the Middle Branch and the surrounding area are reflected in the design decisions. The design focuses on visualizing the hydrology of water in the landscape and creates opportunities for people to be within the water-landscape. Moreover, within this design the dynamic overlap of water and land is used as design tool to interconnect education, health and community within the new park design.


 Alexandra Olivia Torres 


Washington, D.C. has experienced a substantial decline in tree canopy cover during the latter half of the 20th century. Casey Trees, a local non-profit organization, was established with the purpose of stabilizing D.C.'s urban forest. Over 10,000 trees have been planted; however, little is known about the condition or benefits associated with these trees. In order to enhance the sustainability of Casey Trees' planting program, I established baseline rates of condition and mortality and created a set of management recommendations based on numerous pre-planting, environmental and socioeconomic variables. Tree mortality was found to be high, with 24-34% of trees not surviving the first few years of growth. Nursery, planting time, landuse, space type, jurisdiction and numerous socioeconomic variables had a significant effect on tree survival. This study suggests that active programmatic decisions can be made to help reduce new tree mortality and ultimately enhance the long-term production of urban tree-based benefits.

John Christopher Majstrik 

Modeling Nitrogen, Phosphorus and Water Dynamics in Greenhouse and Nursery Production Systems 

Nutrient and sediment runoff from the six states and Washington, DC that form the Chesapeake Bay watershed is a major cause of environmental degradation in the Bay and its tributaries. Agriculture contributes a substantial portion of these non-point source loads that reach the Bay from its tributaries. Research in this area has traditionally focused on agronomic farm contributions, with limited research on the nursery and greenhouse industry. This research presents the first known attempt to model operation-specific information, validated by published research data, where multiple variables are assessed simultaneously. This research provides growers and researchers with a tool to assess and understand the cultural and environmental impact of current practices, and predict the impact of improving those practices. Separate models were developed for greenhouse, container-nursery and field-nursery operations, since specific production variables and management practices vary. Each model allows for simple entry of production input variables, which interface with the Stella modeling layer. Each model was first calibrated with one published research study, and subsequently validated with another peer-reviewed study, with multiple independent runs for each model. Validation results for all three models showed consistent agreement between model outputs and published results, increasing confidence that models accurately process all input data. Verified models were then used to run a number of what-if scenarios, based upon a database of production practices that was gathered from 48 nursery and greenhouse operations in Maryland. This database provided a detailed analysis of current practices in Maryland, and adds significantly to our understanding of various operational practices in these horticultural industries. Results of the what-if scenarios highlighted model sensitivities and provided answers to hypotheses developed from the analysis of the management database. Some model functions, such as denitrification, would greatly benefit from additional research and further model modification. Models were designed to be easily adapted to local conditions for use throughout the U.S. and potentially other parts of the world.

Wei Xing 


This thesis is a design study of a residential community in Langley Park, Maryland with a diverse international population, a mix of mid-twentieth century housing stock, and a car-oriented commercial center. Langley Park will experience dramatic changes over the next ten years as the proposed transit center and light rail line is realized. The study proposes a new way for landscape architects to approach community design. It suggests that by consulting the scholarship of place attachment, designers can develop design strategies and apply them in design practice. Five strategies are proposed. Following a site analysis which identified assets and problems, the author established design objectives that would enhance the community's character and repair damage caused by a lack of connectivity. This thesis suggests designers can incorporate the concepts found in the literature of place attachment and thereby develop strategies to successfully achieve the design objectives.

Kameron Reza Aroom

Riverpark: Adaptive Reuse of South Capitol Street Bridge

This thesis proposes the adaptive reuse of the Frederick Douglass Memorial Bridge, located in Washington, D.C. into an urban park dedicated to the pedestrian experience. Also named the South Capitol Street Bridge, the bridge currently serves as the vital connection between the north and south quadrants of the District of Columbia. With plans to replace the existing bridge, and by utilizing the existing infrastructure, Riverpark will serve as the green link enhancing the pedestrian and cycling experiences between the Capitol Riverfront and Poplar Point across the Anacostia River in southeast Washington.

Chris Patrick Ryan 


Dollar spot (Sclerotinia homoeocarpa) is a common and destructive disease of creeping bentgrass (Agrostis stolonifera). The frequency and severity of dollar spot epidemics has not been quantified and there are no effective predictive models. High rates of nitrogen (N) reduce dollar spot injury, but low N rates applied in summer have not been assessed for disease suppression. Field studies were conducted from 2008 to 2010 with the following objectives: a) to describe the relationship among season, environmental factors and the severity of dollar spot epidemics in six creeping bentgrass cultivars; b) to evaluate six water soluble N sources applied at a low rate (7.3 kg N ha<super>-1</super>) in summer for their impact on dollar spot severity; and c) to assess the performance of low fungicide rates tank-mixed with N on dollar spot severity. Two epidemics were observed each year between spring and mid- autumn, with the second being most severe. A third, late autumn epidemic also was observed in each year. The first epidemic in May was effectively predicated using a degree day model having a biofix date of 1 April and a 15°C base temperature. Ammonium sulfate was most consistently effective in reducing dollar spot injury, but caused foliar injury. Tank-mixing a low chlorothalonil rate with N generally reduced fungicide efficacy.

Patrick Joseph Forrestal 

Corn Residual Nitrate and its Implications for Fall Nitrogen Management in Winter Wheat 

Corn (Zea mays, L.) production typically requires supplemental nitrogen (N) to optimize yields. In dryland corn production systems, where N is applied during the early to mid-vegetative growth stages, inappropriate N applications or limited moisture during the growing season can result in large disparities between optimum and applied N rates. This leads to variable post-harvest residual nitrate (NO3-N) accumulation, which is susceptible to loss. However, this NO3-N could provide the starter N requirement of the subsequent winter wheat (Triticum aestivum, L.) crop. Accounting for residual NO3-N present at wheat planting is important to avoid compounding N loss potential due to corn residual NO3-N accumulation. The objectives of this study were to 1) examine plant based tools for assessing soil NO3-N; 2) to examine post-harvest residual NO3-N accumulation patterns following corn production; 3) to determine optimum fall starter N rates for winter wheat production; and 4) to identify a soil NO3-N level above which starter N could be forgone without negative agronomic effect. This study found that plant canopy measurements are useful tools for assessing corn N management and for identifying drought sites, which had the greatest NO3-N accumulations. The corn stalk nitrate test was significantly (p<0.001) and positively correlated with soil residual NO3-N (r2=0.41). Greatest soil residual NO3-N accumulation occurred where drought conditions reduced production. The agronomic optimum fall starter N rate for winter wheat in Maryland is 17 to 34 kg N ha-1 where soil NO3-N concentration to 15 cm depth is less than 15 mg kg-1. However, the fall starter N response was highly variable and declined significantly (p<0.01) as fall precipitation after planting increased. The results of this study indicate that residual NO3-N levels at planting should be considered before applying fall starter N to winter wheat.

Elizabeth Reed


Fusarium head blight (FHB), caused by Fusarium graminearum, is a destructive disease of the soft red winter wheat grown in the Mid-Atlantic region. Management of FHB focuses primarily on foliar fungicides or cultivar resistance. The purpose of this research was to examine how type II resistance (resistance to spread of the pathogen) is affected by multiple infections along the spike. The combination of type II resistance and fungicide as a way to manage FHB was evaluated in both the greenhouse and field settings. Finally, the role of increased foliage density in an integrated pest management program that included fungicide and cultivar resistance was also evaluated. Multiple infections occurring along a single wheat spike can overwhelm the type II resistance present in some cultivars. The combination of type II resistance and fungicide was the best management practice for FHB than either alone. Foliage density did not improve FHB disease ratings.

Lydia Ann Cardwell 

Scab Resistance QTLs are Associated with Quality and Agronomic Traits of Soft Red Winter Wheat 

Fusarium head blight (FHB) is a devastating fungal disease affecting Triticum aestivum crops worldwide. While many quantitative trait loci (QTL) responsible for FHB resistance have been reported, some widely used sources are from exotic cultivars that may carry undesirable alleles linked with resistance. Ning_7840, a Chinese hard red spring wheat, contains a major FHB QTL on the 3BS chromosome, along with two minor QTL on the 5A and 2DL chromosomes. Ning_7840 was crossed with Pioneer_2643, a soft red winter wheat, to create 86 recombinant inbred lines. The effect of the Ning_7840 alleles on agronomic traits and milling and baking quality traits was examined over three growing seasons in Maryland. While the 3BS QTL was not associated negatively with other traits, the 2DL and 5A QTL were. This suggests the introduction of FHB resistance QTL on 5A and 2DL into soft red winter wheat may negatively affect agronomic and quality traits.


Donna Marie Pahl

Comparing Source of Agricultural Contact Water and the Presence of Fecal Indicator Organisms on the Surface of 'Juliet' Grape Tomatoes 

Microbial water quality standards exist to prevent food safety outbreaks due to the use of agricultural water, although little is known about how the levels the fecal indicator organisms in water relate to the counts on the tomato fruit surface. This study used fecal indicator organisms commonly used in microbial water quality standards (Enterobacteriaceae, total coliforms, fecal coliforms, and <italic>E. coli</italic>) to monitor the water quality of surface ponds, a groundwater source, and the phyllosphere of treated grape tomatoes over two growing seasons. Water source and date caused a significant difference in the counts of fecal indicator organisms. Variability in bacterial counts was found in the surface water sources over the course of the season, partially explained by environmental variables such as water temperature, pH, precipitation, and air temperature. The microbial counts on the surfaces of the tomato fruit did not reflect the water treatments applied to the plants.

 Yenjung Lai 

Kinetics of Tetrachloroethene-Respiring Dehalobacter and Dehalococcoides Strains and Their Effects on Competition for Growth Substrates 

The chlorinated solvents tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. Reductive dechlorination of PCE and TCE at contaminated sites is commonly carried out by dehalorespiring bacteria that utilize these compounds as terminal electron acceptors, but often results in the accumulation of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), rather than non-toxic ethene. This project focused on evaluating how interactions among dehalorespiring populations that may utilize the same electron acceptors, electron donors and/or carbon source may affect the extent of PCE dechlorination in situ. These interactions may be particularly important if both Dehalococcoides ethenogenes (Dhc. ethenogenes) and Dehalobacter restrictus (Dhb. restrictus) are present because these bacteria utilize the same electron donor (H2) and both respire PCE and TCE. However, unlike Dhc. ethenogenes, Dhb. restrictus cannot dechlorinate PCE beyond cDCE. Therefore, the outcome of the population interactions may determine the extent of detoxification achieved. Monod kinetic parameter estimates that describe chlorinated ethene and electron donor utilization by Dhc. ethenogenes and Dhb. restrictus at non-inhibitory substrate concentrations were obtained in batch assays. Substrate inhibition effects on both populations were also evaluated. Highly chlorinated ethenes negatively impacted dechlorination of the lesser chlorinated ethenes in both populations. In Dhc. ethenogenes, cometabolic transformation of VC was also inhibited by the presence of other chlorinated ethenes. PCE and TCE dechlorination by Dhb. restrictus was strongly inhibited by VC. The microbial interactions between Dhc. ethenogenes and Dhb. restrictus was investigated using reactors and mathematical models under engineered bioremediation and natural attenuation conditions. Under engineered bioremediation conditions, Dhc. ethenogenes became the dominant population, and the modeling predictions suggested that the inhibition of Dhb. restrictus by VC was a key factor in determining this outcome. Dechlorination rates by Dhb. restrictus appeared to be affected very little by low acetate concentrations under natural attenuation conditions, giving it an advantage over Dhc. ethenogenes, which requires relatively high acetate concentrations. This study highlighted that substrate interactions among dehalorespiring bacteria can influence their performance and contaminant fate under common bioremediation scenarios. A better understanding of the factors affecting the outcomes of these microbial interactions was achieved, which should aid in the design of successful bioremediation strategies.

Karen Lyn Grubb 

Utilization of Gypsum as a Filter Material in Agricultural Drainage Ditches: Impacts of Land Application on Soil Fertililty Conditions 

Agricultural drainage ditches can provide a direct connection between fields and surface waters, and some have been shown to deliver high loads of phosphorus (P) to sensitive water bodies. A potential way to reduce nutrient loads in drainage ditches is to install filter structures containing P sorbing materials (PSMs) including gypsum to remove P from ditch flow. One projected advantage would be the potential application of spent PSMs to agricultural fields to provide nutrients for crop production after the filter has lost its effectiveness. The study evaluated the feasibility of this strategy. Gypsum was saturated at two levels on mass basis of P, and applied to two soil types, a silt loam and a sandy loam and applied at both a high and low rate. The treated soils were incubated at 25° C, and samples were collected at 0, 1, 7, 28, 63, 91, 119, and 183 days after saturation.

Sonia Lorelly Solano Torres 


Extensive green roof systems can mitigate urban stormwater by capturing rainfall and reducing runoff volume. Green roof substrates, often made from expanded shales, slates and clays are fundamental for roof hydraulic dynamics, and for providing optimal plant growth conditions. However, these substrates occasionally impose load limitations for retrofitting existing infrastructure. This research studied recycled-tire crumb rubber, as a light-weight material for amending green roof substrates. Zinc release from crumb rubber was quantified, and the interactions with commercial rooflite® substrate and the effect of high Zn concentrations on the growth and uptake by Sedum were studied. Zn was found to leach from crumb rubber in quantities that could negatively affect plant growth; however, Zn was adsorbed onto cation exchange sites of the mineral and/or organic portion of rooflite®, preventing negative growth effects in Sedum. Crumb rubber could be utilized as an amendment with substrates having high cation exchange capacities.
Adam Lincoln Gray

Redoximorphic Features Induced by Organic Amendments and Simulated Wetland Hydrology 

During wetland construction, it is common to add organic amendments to the soil, although little research has evaluated the effects of organic additions on the development of redoximorphic features. The objective of this study was to evaluate the effects of adding different types of organic materials, using different methods of incorporation, on the formation of redoximorphic features under hydric soil conditions. Five types of organic materials were incorporated into soil cores lacking redoximorphic features, using three incorporation methods. Cores were established as mesocosms in a controlled greenhouse environment or transplanted into a natural wetland. Mesocosms were periodically dissected and examined for newly formed redoximorphic features. The method of incorporating organic materials had a significant influence on the development of redoximorphic features, but the type of organic material had no significant effect. Organic materials should be concentrated into deeper zones during wetland construction to maximize development of redoximorphic features.

Allen Dawson

Ecological Values and Ecosystem Services of Natural Forests: A Study of Prince William Forest Park, Virginia 

Abstract The Urban Forest Effects (UFORE) model developed by the USDA Forest Service quantifies the ecological benefits of urban forests. UFORE has been used to analyze many urban areas, including National Park land in Washington, D.C., but has not been applied to natural forests. We conducted a UFORE analysis of Prince William Forest Park for species composition and individual tree characteristics including tree height, DBH, canopy architecture, and general tree health, collecting data during the 2007 field season. The results show that the park contains over 6,287,000 trees and these trees store 394,000 tons of carbon with an annual net sequestration rate of 12,300 tons. This forest also abates 414 tons of air pollution annually. These results quantify and affirm to policymakers and the public the value and ecological importance of the forests managed by the National Park Service surrounding metropolitan Washington, D.C.

 Yvonne Elizabeth Lawley 

Weed Suppression By Forage Radish Winter Cover Crops

Forage radish (Raphanus sativus L. var. longipinnatus) is a new winter cover crop in the Mid-Atlantic region. This study had three objectives: 1) to characterize the repeatability, amount, and duration of weed suppression during and after a fall-planted forage radish cover crop 2) to quantify its subsequent effect on direct seeded corn, and 3) to identify the mechanisms of this weed suppression. Forage radish cover crops were grown in ten site-years and followed by a corn crop in seven site-years in the coastal plain of Maryland. Forage radish was compared to rye (Secale cereale L.), oat (Avena sativa L.), and no cover crop treatments. Early and typical corn planting dates along with contrasting herbicide management strategies were compared over four site-years. Forage radish did not reduce population or yield in subsequent corn crops. Forage radish provided complete suppression of winter annual weeds in the fall and early spring but the suppression did not persist into the following cropping season. When forage radish cover crops were used in place of pre-plant burn down herbicide treatments to control weeds in early planted corn, some weeds were present at the time of corn emergence but corn yields were not reduced if emerged weeds were controlled with a postemergence herbicide. Controlled environment bioassays involving cover crop amended soil, aqueous plant extracts, and aqueous soil extracts along with a field experiment involving planted weed seeds did not provide evidence of allelopathy. In a residue moving experiment, no difference in spring weed suppression was observed if forage radish residues were removed prior to killing frost in November or left in place to decompose in three of four site-years. These results were supported by planting date experiments where fall ground cover and spring weed suppression was greatest for earlier planting dates of forage radish cover crops. Thus, rapid and competitive fall growth, rather than allelopathy, is the most likely mechanism of weed suppression by forage radish winter cover crop. Strategies to utilize the weed suppression of forage radish cover crops should focus on fall weed suppression and the early spring pre-plant window of weed control.

Jing Kang 


Fusarium Head Blight (FHB) of wheat (<italic>Triticum aestivum</italic>), caused by <italic>Fusarium graminearum</italic>, is a disease that periodically strikes the mid-Atlantic region of the USA. Breeding for resistant wheat cultivar is an effective method of disease control. McCormick, a genotype adapted to the mid-Atlantic region, was used in a backcross program with the Chinese cultivar Ning7840. Eight Near-Isogenic Lines (NIL) were developed by marker-assisted backcrossing. Three FHB resistance QTL on chromosomes 3BS, 2DL, and 5A were introgressed from non-adapted Ning7840 into the elite soft red winter wheat McCormick. The objective of this study was to evaluate the effects of QTL singly and in combination on FHB resistance. The 3BS+2DL NIL showed higher resistance and lower deoxynivalenol content than other NIL in both field and greenhouse studies. This suggests that the 3BS+2DL NIL can be used in the mid-Atlantic region to breed for improved FHB resistance.


Felix Ruben Rodriguez Arguedas 


The nursery and greenhouse industry requires precise methods to schedule irrigations, since current practices are subjective and contribute to water and nutrient runoff. Capacitance sensors were calibrated to precisely estimate substrate water content, matric potential, and pore water electrical conductivity (EC) in five soilless substrates. Regression coefficients (R<super>2</super>) ranged from 0.29 - 0.88 and 0.16 - 0.79 for water content in 5-cm and 20-cm column heights; matric potential R<super>2</super> ranged from 0.10 - 0.98 and 0.79 - 0.98, respectively. Pore water EC calibrations were investigated, contrasting two sensor types and two prediction models. Results were applied to an empirical greenhouse dataset. Better precision and accuracy were achieved with ECH<sub>2</sub>O-TE sensor and Rhoades model. Capacitance sensors provide precise estimates of plant-available water in most soilless substrates, while pore water EC accuracy and precision depends on the sensor-model combination. These results will enable growers to precisely schedule irrigations based on water content and pore water EC.

Joshua Daniel Nadler


Methods for in vitro induction of polyploid Cercis yunnanensis Hu et Cheng using oryzalin were developed and evaluated. Methods included treating either shoot or callus tissue for different exposure durations with either an aqueous solution of 150 micromolar oryzalin or the addition of oryzalin directly to solid media. Polyploid nuclei were determined by flow cytometry for all oryzalin treatments. Although the results indicate that most tissues measured were likely chimeras with respect to DNA content. Results indicate that treating shoot tissue with an aqueous solution of oryzalin for 12 to 96 hours produced tetraploid plants irrespective of the type of shoot explant treated. An unstable octaploid was formed from the treatment of a pre-cultured lateral shoot in an aqueous solution of oryzalin for 96 hours. In contrast shoots cultured on the solidified media failed to produce polyploid plants and there were no statistical differences between callus treatments regarding polyploid induction.

Guihua Chen 

Alleviation of Soil Compaction by Brassica Cover Crops 

Soil compaction is a worldwide problem in modern agriculture associated with overuse of heavy machinery and intensification of cropping systems. Though tillage is traditionally used to alleviate compaction effect, increasing concerns about environmental impacts of tillage have led to interest in conservational tillage systems and incorporation of cover crops into crop rotations. Previous study showed soybean (Glycine Max L.) roots grew through a plowpan soil using channels left by canola (Brassica napus) cover crop roots, a process termed "biodrilling" to alleviate compaction effect. However, this study did not provide any quantitative data to support the observational conclusion. We studied "biodrilling" abilities of three cover crops and the effects of "biodrilling" on corn (Zea mays)/soybean growth by conducting three experiments. The first two experiments included three surface horizon compaction treatments (high, medium and no compaction), four cover crops [FR (forage radish: Raphanus sativus var. longipinnatus, cultivar `Daikon') and rape (rapeseed: Brassica napus, cultivar `Essex') (tap-rooted species in the Brassica family), rye (cereal rye: Secale cereale L., cultivar `Wheeler') (fibrous-rooted species) and NC (no cover crop)] in Exp. 1, and three cover crops (FR, rape and NC) in Exp. 2. The third experiment was conducted on field with a legacy plowpan (subsoil compaction) using FR, rye and NC cover crops. Roots of FR were least inhibited by compaction, while rye roots were severely arrested by compaction. The order of "biodrilling" ability was FR > rape > rye. Soil bulk density, strength and least limiting water range were controlled by compaction treatments. Soil air permeability was greatly reduced by compaction. Air permeability was greater in rape/FR treatments than in rye/NC treatments under high/medium compaction. Corn/soybean root penetrations, subsoil water uptake in the compacted soils were enhanced by FR/rape treatments but not by rye/NC treatments. Compaction decreased corn yield only in Exp. 2 where soil sand fraction was greater. The yield of corn was greater in three cover crop treatments than in NC control. In terms of "biodrilling", Brassica cover crops (FR and rape) were more effective than rye cover crop, would alleviate effects of soil compaction on plant growth in no-till farming systems.

Yusong Mu


Pesticide degradation in turf is complicated by presence of an organic matter enriched layer called thatch. It is not well understood how the extensive pesticide sorption capacity of thatch may affect the aerobic degradation of pesticides in thatch. Hollow tine cultivation and vertical mowing are two commonly used cultivation practices used to control thatch. Two studies were conducted to determine how these two cultural practices may affect microbial activity and pesticide degradation within thatch and soil. Hollow tine cultivation briefly enhanced microbial activity within thatch while vertical mowing had no consistent effect on thatch or soil microbial activity. Neither cultivation practice consistently altered the aerobic degradation of 2,4-D, flutolanil or chlorpyrifos. Thatch and soil aerobic degradation constants obtained for flutolanil and chlorpyrifos supported the hypothesis that strongly adsorbed pesticides are shielded from microbial populations that degrade pesticides within thatch.

Kimberley Ellen Mead


With the exponential growth in human population and rapid increase in global urbanization, understanding changes in community dynamics and structure in human dominated landscapes is essential, yet, rarely studied. To determine what factors account for tree species composition and distribution in an urban setting, data from the 1999 UFORE Model vegetation survey of Baltimore, Maryland was analyzed. There was a diverse arboreal population found, comprised primarily of species native to the area. Detrended correspondence analysis did not show a clear pattern of species assemblages based on land-use, possibly indicating a homogenization of conditions across the urban environment. In canonical correspondence analyses, species distribution could not be explained by socioeconomic factors, however, there was a significant relationship of tree species assemblages and the physical environment, specifically with percent impervious surface cover. The amount of variance accounted for was small indicating that other factors may be involved in determining tree species distribution.

Charles Macaulay White 

Forage Radish Cover Crop Effects on Mycorrhizal Colonization and Soil Test Phosphorus 

Forage radish (Raphanus sativus L. var. longipinnatus) and cereal rye (Secale cereale L.) cover crops were examined for their effects on arbuscular mycorrhizal colonization and P acquisition of a subsequent corn (Zea mays L.) silage crop. Soil test P following these cover crops was also measured in bulk soil collected at three depths in the surface soil and in soil sampled within 3 cm of forage radish tap root holes. Forage radish never decreased mycorrhizal colonization and rye sometimes increased colonization of the subsequent crop compared to growing no cover crop. The extent of colonization of corn roots by arbuscular mycorrhizal fungi was positively correlated with corn shoot tissue P concentrations. Slight vertical soil test P stratification in the bulk soil occurred following both forage radish and rye cover crops at some sites. A large increase in soil test P occurred within 3 cm of forage radish tap root holes.

Ray L. Pigati 

Factors Affecting Fungicide Performance when Targeting Dollar Spot Disease in Creeping Bentgrass 

Creeping bentgrass (Agrostis stolonifera) is commonly grown on golf course fairways and dollar spot (Sclerotinia homoeocarpa) is perhaps the most chronically severe disease of bentgrass. Field studies were conducted to: a) determine the influence of simulated rainfall and two mowing timings (AM and PM) on the performance of four fungicides, and b) to assess the effects of two fungicide spray volumes (468 and 935 L water ha-1) and application timings (AM and PM) on dollar spot control in creeping bentgrass. Fungicide effectiveness generally was reduced by simulated rain imposed about 30 minutes after application. Boscalid and chlorothalonil were most and least rain-safe; respectively, and propiconazole and iprodione were intermediate in rain-safeness. Fungicide performance was improved by mowing in the AM prior to fungicide application. A tank-mix of chlorothalonil + propiconazole was unaffected by spray volume or application timing, but the performance of chlorothalonil and propiconazole applied separately was inconclusive.

Philip Klaus Zurhelde 


Some loamy textured soils along the Mid-Atlantic coastal plain undergo extended periods of saturation or ponding, yet lack the hydromorphology that identifies them as hydric by any of the currently approved Field Indicators of Hydric Soils (FI). Termed Anomalous Bright Loamy Soils (ABLS), these were identified at four research sites on the Delmarva Peninsula. The hydrologic and biogeochemical status of these soils was monitored for three years along a hydrosequence at each site. A series of field and lab experiments were run to investigate the possible causes for the ABLS-phenomenon. The most likely cause is a combination of low hydrologic gradient coupled with the length of time since saturation. Using observed morphology, a newly developed Field Indicator successfully discriminated between five hydric soils that lacked an approved indicator and those that were not hydric. This indicator has now been approved as an official FI of Hydric Soils (F20)


Andrea Ottesen 

Microbial Ecology and Horticultural Sustainability of Organically and Conventionally Managed Apples

Objectives: Organically and conventionally managed apple trees (Malus domestica Borkh) were evaluated for three growing seasons (2005-2007) to examine the impact of organic and conventional pesticide applications on the microbial ecology of phyllosphere and soil microflora. An important objective was to establish if organic or conventional selection pressures contribute to an increased presence of enteric pathogens in phyllosphere microflora. The horticultural and economic sustainability of the organic crop was also compared to the conventional crop with regard to fruit yield and input costs. Methods: Microbial populations from phyllosphere and soil environments of apple trees were evaluated using clone libraries of 16S rRNA gene fragments. Clones were sequenced and software was used to assess diversity indices, identify shared similarities and compute statistical differences between communities. These measurements were subsequently used to examine treatment effects on the microbial libraries. Phyllosphere Results: Eight bacterial phyla and 14 classes were found in this environment. A statistically significant difference between organically and conventionally managed phyllosphere bacterial microbial communities was observed at four of six sampling time points. Unique phylotypes were found associated with each management treatment but no increased human health risk could be associated with either treatment with regard to enteric pathogens. Soil Results: Seventeen bacterial phyla spanning twenty-two classes, and two archaeal phyla spanning eight classes, were seen in the 16S rRNA gene libraries of organic and conventional soil samples. The organic and conventional soil libraries were statistically different from each other although the sampling depth was not sufficient to make definitive inference about this environment. Horticultural Results: Fruit yields from organically managed apple trees were from one half to one third of the yields from conventionally managed trees. Based on input costs, organic fruit was about twice as expensive to produce. Asian pears (Prunus serotina) were also included in this horticultural analysis and showed greater field tolerance as an organic specialty niche crop than apples.

Rebecca Bourgault 

Multi-Scale Pedologic Investigation of Manganiferous Soils in the Maryland Piedmont 

Manganese oxides are usually found in trace quantities in soils, but they are important due to their effects on soil chemistry and morphology. There are rare soils in the Maryland Piedmont that have extremely high amounts of manganese oxides that have not been previously studied. These manganiferous soils were examined at multiple scales in order to determine their spatial extent, to characterize their fundamental morphology, mineralogy, and chemical and physical properties, and to better understand their pedogenesis. The soils occupy areas of 1-2 ha in size, within 200 km<super>2</super> in eastern Frederick County and western Carroll County. The soils can have as much as 140 g kg<super>-1</super> Mn as oxides, which pigments the entire soil matrix black in subsoil horizons. It appears that the black, porous, Mn-rich material is derived directly from the dissolution of marble bedrock and accumulation of silicate residues plus Mn and Fe from within the rock.

Eun-Young Hwang 

Association Analysis in Soybean 

Association analysis is a new approach to identify the location of gene(s)/allele(s) of interest. There are a number of factors determining the feasibility of whole-genome association analysis which include the level of linkage disequilibrium (LD) and the magnitude of population structure in a population. The goal of this study was to evaluate the success of whole-genome association analysis in soybean germplasm accessions using DNA markers across the whole genome. Firstly, the extent of LD and the presence of population structure were estimated. Secondly, whole-genome association analysis was performed to detect the location of the allele/gene controlling flower color, pubescence color, and seed protein quantitative trait loci (QTLs) in 319 soybean [<em>Glycine max</em> (L.) Merr.] germplasm accessions. The soybean germplasm accessions had a relatively low level of LD which declined very rapidly to 0.8 in less than 4 Kbp as indicated by r<sup>2</sup> as well as highly diverse population structure. Despite the low LD and the presence of high population structure, whole-genome case-control analysis successfully detected the 65 bp insertion in the <em>GmF3'5'H</em> (GenBank acc. AY117551) gene controlling purple <em>vs</em>. white flower color, as well as a single base deletion in the <em>F3'H</em> (GenBank acc. AB191404) gene controlling tawny <em>vs<\em>. gray pubescence color. However, there were 28 gray pubescence lines that did not contain the deletion suggesting that there is a second mutation determining the pubescence color alteration. In the case of seed protein QTL, whole-genome regression analysis detected one of four previously reported seed protein QTLs which reside on linkage group (LG) E and a new seed protein QTL on LG K. The detection of three other previously reported seed protein QTLs on LGs A1, I and M was not successful. It is unclear why association analysis was not successful in the detection of the three previously reported QTLs. However, a number of reasons including incomplete adjustment for population structure, lack of statistical power, an inadequate number of genetic markers in light of the low level of LD, and the power of association analysis to detect alleles with relatively modest genetic effects are suggested as possible reasons.

Dominic Brose 

Oxidation-Reduction Transformations of Chromium in Aerobic Soils and the Role of Electron-Shuttling Quinones in Chemical and Microbiological Pathways 

Soils from three toposequences in Maryland with minimal heavy metal contamination were sampled to investigate oxidation-reduction transformations of chromium in whole soil samples. Chromium (VI) reduction to Cr(III) was observed in all 18 samples, and 11 demonstrated enhanced reduction with the electron shuttle anthraquinone-2,6-disulfonate (AQDS). Oxidation of Cr(III) to Cr(VI) was observed in 12 samples, and 7 samples demonstrated diminished oxidation with AQDS. Lactate was added to the Watchung series to enhance biological activity, and high salt concentration was added to inhibit it. Both treatments reduced Cr(VI) to below detection limits by 11 d, suggesting abiotic reduction. The control treatment demonstrated reduction of Cr(VI) without soil. To further investigate, increasing lactate concentrations were added to Cr(VI) and AQDS. Reduction increased with increasing concentration; 60 mM lactate reduced all Cr(VI) within 1 hr. Other organic acids were tested for similar interactions; tartrate and citrate reduced Cr(VI), which was enhanced with AQDS.

Shawna Joy Behling 

Effects of nitrogen and calcium on photosynthesis and metabolic activity in Acer saccharum in the Catskill Mountains 

The Catskill Mountains in southern New York have received some of the most acidic rainfall in the country for the past 50 years. Acid deposition on these thin soils may deplete the concentration of calcium and other essential ions in the soil solution and mobilize other ions that can be harmful to sugar maple (Acer saccharum) rooting systems. The effects of fertilizers on the metabolism and photosynthesis rates of sugar maple are of great interest to both farmers and ecologists. In this study, 12 plots in a 60-year-old sugar maple dominated forest were treated with no fertilizer, nitrogen, calcium, or nitrogen and calcium together. Photosynthesis was measured with a LiCor 6400. Metabolic heat rate was measured with a MC-DSC calorimeter. While some sampling periods showed significant responses to some treatments, the study as a whole suggests the addition of calcium and/or nitrogen had minimal effects on photosynthesis or metabolism.

Kuang-Yu Chen


MADS-box transcription factors regulate the development of vegetative and reproductive organs in plants. Little is known about the role of MADS-box genes in tree development. Using phylogenetic analysis, 57 putative type II MADS-box genes representing 14 functional classes were identified in the Populus trichocarpa genome. cDNA sequencing of the poplar type II MADS-box genes indicates that 28.1% of the transcripts differed in the intron-exon structures predicted in the genome database and 19.3% of the transcripts appear to be alternatively spliced. The majority of the poplar type II MADS-box genes were expressed in a wide variety of tissues including shoot apices, leaves, bark, xylem, root, and floral tissues and in shoot apices during bud development and dormancy. These results indicate that poplar MADS-box genes have diverse regulatory roles in a broad range of tissues and developmental processes. Six poplar FLC-like genes, PtFLC1-PtFLC6, were identified in the poplar genome and expression of all six genes was detected in poplar shoot apices. The expression of one gene, PtFLC2, declined in apical buds during SD photoperiod and low temperature induced dormancy development suggesting a role in bud dormancy and may represent an analogous regulatory mechanism to the down-regulation of FLC during vernalization in Arabidopsis. In addition, several PtFLC2 splice isoforms (PtFLC2as1-9) were identified that were associated with the later stages of bud dormancy. Overexpression of the PtFLC2as1 isoform delayed photoperiod induced apical bud development and bud dormancy, growth cessation, and leaf senescence while overexpression of the PtFLC2as2 isoform appeared to accelerate bud development and dormancy and reduce the amount of chilling required to overcome dormancy. These findings suggest that PtFLC2, unlike Arabidopsis FLC, could be an integration point for both photoperiod and cold signals that regulate bud development and dormancy. These results also suggest that in addition to transcriptional regulation, that cold-mediated production of PtFLC2 splicing isoforms may have an important regulatory role in bud dormancy. The regulated production of splicing isoforms could regulate bud dormancy either by dominate negative interactions, by forming different protein complexes or regulating different pathways that regulate growth, dormancy, and dormancy release.


Ping Xue 

Physiological and Molecular Studies of Ethylene Effects on Soybean Root Infection by Soybean Cyst Nematodes 

Soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating pests of soybean in the world. Several earlier reports demonstrated that ethylene is involved in nematode feeding cell formation in Arabidopsis and tomato. I investigated whether or not ethylene is involved in SCN feeding cell formation in soybean. My results show that SCN parasitism was increased by treatment of roots with ethylene and inhibited by suppressors of ethylene action or in an ethylene resistant soybean mutant. My results also indicate that excised soybean roots colonized by SCN produced ethylene at 1.5-3 times the rate of non-infected roots between 14 and 22 days post inoculation. To determine if ethylene was being synthesized in feeding cells, an ethylene-responsive promoter fused to a GUS reporter gene was constructed and transformed into soybean roots with Agrobacterium rhizogenes. Overall, the results suggest that ethylene plays an important role in SCN infection in soybean

Danielle Marie Balduff 

Pedogenesis, Inventory, and Utilization of Subaqueous Soils in Chincoteague Bay, Maryland 

Chincoteague Bay is the largest (19,000 ha) of Maryland's inland coastal bays bounded by Assateague Island to the east and the Maryland mainland to the west. It is connected to the Atlantic Ocean by the Ocean City inlet to the north and the Chincoteague inlet to the south. Water depth ranges mostly from 1.0 to 2.5 meters mean sea level (MSL). The objectives of this study were to identify the subaqueous landforms, evaluate the suitability of existing subaqueous soil-landscape models, develop a soils map, and demonstrate the usefulness of subaqueous soils information. Bathymetric data collected by the Maryland Geological Survey in 2003 were used to generate a digital elevation model (DEM) of Chincoteague Bay. The DEM was used, in conjunction with false color infrared photography to identify subaqueous landforms based on water depth, slope, landscape shape, depositional environment, and geographical setting (proximity to other landforms). The eight such landforms identified were barrier cove, lagoon bottom, mainland cove, paleo-flood tidal delta, shoal, storm-surge washover fan flat, storm-surge washover fan slope, and submerged headland. Previously established soil-landscape models were evaluated and utilized to create a soils map of the area. Soil profile descriptions were collected at 163 locations throughout Chincoteague Bay. Pedons representative of major landforms were characterized for a variety of chemical, physical and mineralogical properties. Initially classification using Soil Taxonomy (Soil Survey Staff, 2006) identified the major soils as Typic Sulfaquents, Haplic Sulfaquents, Sulfic Hydraquents, and Thapto-Histic Sulfaquents. Using a proposed modification to Soil Taxonomy designed to better accommodate subaqueous soils with the new suborder of Wassents, soils of Chincoteague Bay were primarily classified as Fluvic Sulfiwassents, Haplic Sulfiwassents, Thapto-Histic Sulfiwassents, Sulfic Hydrowassents, and Sulfic Psammowassents. To illustrate the application of subaqueous soils information, the suitability of soils for submerged aquatic vegetation (SAV) habitat was assessed, based upon past and current growth patterns in Chincoteague Bay and sediment properties known to affect SAV establishment and growth. The refined soil-landscape models and extensive soil characterization obtained in this study have advanced our understanding of subaqueous soils in coastal lagoon systems, and should prove valuable to coastal specialists managing these critical resources.

Meredith Bilek 

Winter annual rye cover crops in no-till grain crop rotations: impacts on soil physical properties and organic matter 

Winter annual cover cropping (WCC) is a common management practice subsidized by Maryland to protect water and soil quality. The affect of long-term incorporation of WCC on soil physical properties (SPP) is not well established. We hypothesized by increasing organic inputs WCC would improve SPP. To evaluate the effect of WCC and wheel traffic (WT) on SPP, we studied two long term rotations (corn/rye and corn/fallow) at two locations on the Coastal Plain (CP) and one on the Piedmont. WCC improved SPP, but only during the winter at the CP. High levels of WT compacted soil in both rotations. WCC and wheel traffic had no effect on SPP or organic matter at the Piedmont. We conclude, only during the winter did WCC improve SPP; however, due to the drastic annual changes, we hypothesize this improvement is due to soil disturbance caused by the grain drill planting the rye.

Lisa Stocking Gruver 

Soil Nematode Communities as Influenced by Cover Crops, with a Focus on Brassicaceae 

The effect of brassicaceous cover crops (Brassica juncea/<em>Sinapis alba, B. napus, and Raphanus sativus) on plant-parasitic and free-living soil nematode communities, in grain agroecosystems, was evaluated in three experiments, at two sites in Maryland. Brassicaceous cover crops alone did not suppress plant-parasitic nematodes, however when combined with rye (Secale cereale) or clover (Trifolium incarnatum), juvenile (J2) Heterodera glycines populations were lower in June, soybean yields were higher, or free-living nematode abundance was higher. Indices of free-living nematode community structure suggested that winter-kill of N-rich radishes activated the bacterivore community in early spring resulting in high populations of bacterivore dauer larvae and high community structure by summer. In contrast, nematode communities in spring-terminated rapeseed and rye plots had high abundances of fungivore nematodes and a plant associate/fungal feeder, Coslenchus. Brassicaceous cover crops in Maryland grain rotations may be more useful for managing soil ecology than for biofumigation of plant-parasitic nematodes.

 Chenping Xu

The effects of solar ultraviolet-b on the proteome and antioxidant defense systems in soybean leaves 

Stratospheric ozone depletion has caused an increase in the amount of ultraviolet-B (UV-B) radiation reaching the earth's surface. Some investigations have demonstrated that UV-B has effects on protein accumulation and active oxygen species (AOS) metabolism in plants. Because of the unrealistically high UV-B level and low levels of ultraviolet-A (UV-A) and photosythetically active radiation (PAR) in indoor studies it has been questioned whether results from these studies can be extrapolated to field responses. In the present study two isolines of the soybean cultivar Clark with different flavonoid contents were grown in the field with or without natural levels of UV-B. The leaf proteome and AOS metabolism were examined. Ambient solar UV-B radiation changed AOS metabolism by decreasing superoxide dismutase activity and increasing the activities of ascorbate peroxidase, catalase and glutathione reductase relative to UV-B exclusion treatments. This resulted in decreased ascorbic acid and increased dehydroascorbate content. Proteomic analysis showed that the accumulations of 67 protein spots were significantly affected by solar UV-B. Proteins related to photosystems in photosynthesis were increased in abundance while enzymes involved in the primary carbon and nitrogen metabolism were decreased. This could lead to overreduction of the photosynthetic electron transport chain and enhance the formation of superoxide radicals and singlet oxygen. The magenta line, which has reduced flavonoid levels, had greater proteomic and oxidative responses than the standard line, suggesting that flavonoids act as screening compounds and antioxidants in protecting plants from UV-B radiation. These line-specific differences occurred even under UV-B exclusion, which may be due to high UV-A, PAR or temperature. More detailed studies are needed to elucidate the effects of other environmental factors on the soybean leaf proteome and AOS metabolism under field conditions.


Olivia Harcourt Deverux 

Quantifying Fine Sediment Sources in the Northeast Branch of the Anacostia River, Maryland, Using Trace Elements and Radionuclides 

Fine sediment sources were characterized in an urban watershed, the Northeast Branch of the Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible sediment sources and suspended sediment collected at the watershed outlet during storm events. Methodology for selecting tracers was developed so the sediment fingerprinting method could effectively determine the relative quantity of sediment contributed by each source to the suspended fraction. The amount of enrichment of trace elements in sediment sources and suspended sediment was determined by calculating enrichment ratios, which are ratios of the normalized concentration of elements in the sample relative to their average normalized concentration in the Earth's upper continental crust. Streambanks contributed the highest relative quantity of sediment in the fall and spring while upland areas contributed mostly during winter. Street residue contributed 12% on average and was the source most concentrated in anthropogenically enriched elements.

Won Jun

Structure-function relationships of periplasmic membrane-derived oligosaccharides in salmonella growth and virulence 

Membrane-derived oligosaccharides (MDO) consist of branched substituted &#946;-linked sugar chains that are present in the periplasmic space of Escherichia coli and other gram-negative bacteria. Their common features are the presence of glucose as a major constituent sugar and their increased levels in low-osmolarity media. In several phytopathogenic bacteria, mutants defective in MDO synthesis failed to incite disease on the host plant. Very little is known about the role of MDO from Salmonella in virulence and osmotolerance. I have studied the structure-function relationship of MDO to understand if they play a role in Salmonella growth and virulence. MDO defective mutants of Salmonella Typhimurium were generated using a gene specific mutagenesis protocol and MDO were isolated and their glycosyl composition analyzed. The fractions containing the major peak from Sephadex G-10 gel filtration chromatography were pooled and subjected to DEAE-cellulose anion exchange chromatography to separate charged and neutral MDO. Compositional analysis revealed that MDO of wild-type consist of 94% glucosyl residues (hereafter referred to as glucose) in Salmonella Typhimurium FIRN while MDO of the delta mdoG mutant was comprised of only 24% glucose. Rhamnose, mannose, and galactose accounted for the rest. We also found that MDO composition varies in different chromosomal backgrounds. For example, glucose accounted for 41% of sugar residues in MDO of Salmonella Typhimurium SL1344. This proportion was further reduced to 24% in the delta mdoG mutant. Salmonella Typhimurium delta mdoG mutants (in FIRN as well as SL1344 chromosomal backgrounds) displayed reduced virulence in mice. Salmonella Typhimurium SL1344 delta mdoG mutant strain was recovered from the intestinal tissues and systemic tissues at a lower frequency than its parental wild-type strain and displayed a reduced ability of intracellular replication in macrophages. This defect in the delta mdoG mutant could be associated with the altered MDO composition. The delta mdoG mutant also invaded macrophages at a reduced efficiency and showed lower respiration rate under conditions mimicking acidic environments, such as stomach and phagosomes (pH 5.0). Correspondingly ATP level in the delta mdoG mutant was significantly reduced compared to the wild-type. These results support an important role for MDO in the virulence of S. Typhimurium. In competition assays using a mouse host, the delta mdoG mutant had a reduced capacity to colonize the mouse tissues. On the contrary, competitive assays on laboratory media showed that the mdoG mutation enhanced the growth of bacteria. A mixed pictured emerged when competition assays were performed by artificially inoculating fresh-cut produce. On tomato and cucumber, the wild-type cells emerged as dominant population after 3 days of growth, while no one strain dominated during the growth on honeydews, cantaloupes, watermelons, as well as acidic fruits such as apples. Together, these data demonstrate that specific wild-type MDO are required for efficient colonization and optimal virulence in mice. For environmental survival under different niches, no evidence was found for a specific need for MDO with particular sugar composition. Enteric pathogens with altered MDO (and reduced virulence) may serve as better "live vaccines".

Minggang Wu

Characterization of PtFD1, a bZIP transcription factor using transgenic poplars 

Dormancy is an adaptive mechanism that enables plants to survive unfavorable environmental conditions and resume growth when the conditions become favorable again. Bud formation is the morphological event associated with bud dormancy. The research presented in this thesis focuses on the role of PtFD1, a bZIP transcription factor, in apical bud development in poplar. This research included the construction of binary Agrobacterium vectors for the overexpressing of PtFD1 and for down regulation or silencing of PtFD1 expression using RNAi technology. These vectors were used to create transgenic poplars (Populus alba×Populus tremula) with altered expression of PtFD1. The overexpression of PtFD1 prevented apical bud development while apical bud development appeared normal in PtFD1 RNAi expressing plants. Flowering was also induced in long days in poplars overexpressing PtFD1. Anatomical studies indicate that overexpression of PtFD1 impinges on bud scale development during short day induced bud formation.

Amy Kremen 

Nitrogen Mineralization from Brassica Cover Crops 

The potential of forage radish (<em>Raphanus sativus</em> L.), rape (<em>Brassica napus</em> L.), and rye (<em>Secale cereale</em> L.) cover crops to capture residual nitrogen and then provide early season N to subsequent main crops via mineralization from their residues was compared. At four field experiments established in Maryland (2003-2005), N uptake by radish and rape equaled or exceeded that by rye. No differences in soil inorganic N due to cover crop type were observed during spring 2004. In spring 2005, greatest N release from forage radish residues (March-May) was followed by that from rape residues (May-June). Brassica decay significantly increased growth of immature corn and soybean plants. In a 48-day incubation study comparing N mineralization in fine and coarse textured soils from Brassica and rye root or shoot residues, N mineralization was greatest from forage radish and rape shoots. Compared with rye, the Brassica cover crops showed environmental and agronomic promise

Jill Elise Dean 

Brassica Cover Crops for Nitrogen Retention in the Maryland Coastal Plain 

The Brassica cover crops, forage radish (Raphanus sativus L. cv 'Daichon'), oilseed radish (Raphanus sativus L. cv 'Adagio'), rape (Brassica napus L. cv 'Dwarf Essex'), and cereal rye (Secale cereale L. cv 'Wheeler') were examined for ability to decrease mineral N losses and influence organic N cycling at two Maryland Coastal Plain agricultural sites. Brassicas were similar or superior to rye regarding N uptake and soil profile NOsub3-N depletions (105-180 cm depth). Rape and rye maintained soil porewater NOsub3-N below 3 mg L to the minus 1 throughout spring while radish performed similarly on fine-textured soil, but caused porewater NOsub3-N > 10 mg L to the minus 1 on coarse-textured soil. Dissolved organic N averaged 51% of total N in porewater, but was unaffected by cover crops. Brassicas were as effective as rye in minimizing mineral N losses, but the role of cover crops in managing organic N was unclear.

Banu Saritas-Yildirim 

Characterization and Expression of RUB1 Conjugase and Cullin1-like Genes in Poplar Associated with Vegetative Bud Development and Dormancy 

Dormancy is an adaptive trait that ensures survival of plants in adverse growth conditions. By using phylogenetical, expression, and protein analysis, RUB1 conjugase and Cullin1 were characterized in poplar dormancy. RUB1 conjugase and Cullin1 were annotated using sequence homology approach. RUB1 conjugase was expressed in apical buds during dormancy but not detected in those of etr1-1 expressing poplars. Its transcript abundance was reduced in axillary buds, leaves and bark of etr1-1 expressing poplars compared to wild types. RUB1 conjugase expression was not affected by AVG but reduced by 50µM ACC in apical buds of etr1-1 expressing poplars. Cullin1 and EBF expression did not display significant difference in most tissues except for the Cullin1 expression in middle and bottom leaves during short-day treatments in wild types. Two novel RUB1-conjugated proteins were detected during low temperature treatments. This study has built a foundation for further analysis of targeted protein degradation in dormancy.


Mitchell Louis Scott

Mapping and Characterization of the Marlboro Clay Formation 

The Marlboro Clay formation is a geologic formation that outcrops in Prince George's County, Maryland, and is of great significance due to its instability. Water well logs are collected to determine ground water quantity. Marlboro Clay can be easily recognized in the water well log's lithology descriptions due to its pink color. The objectives of this study were to provide data on the morphology and problematic characteristics of soils formed from Marlboro Clay to and use water well log data to create an interpolated Marlboro Clay map. Marlboro Clay samples were smectite and kaolinite dominated and had moderate potential volume change ratings. The particle size varied due to infilling of sediments from the overlying Nanjemoy and underlying Aquia formations. An accurate bottom elevation Marlboro Clay map was created which we strongly anticipate will contribute to improved natural resource and urban planning activities where the Marlboro formation is foun

Joseph Robert Ferrari  


Connectivity is critical for persistence of species in the face of anthropogenic habitat destruction and fragmentation. Graph theory is a relatively new method for quantifying connectivity that has tremendous potential, but landscape graph applications to date are limited to specific conservation situations with static proportions of habitat (P). This study provides a uniform evaluation of graph metrics across wide gradients in P in both random neutral landscapes and real, forested landscapes from the Mid-Atlantic region of the United States. Such an analysis provides a background that will be valuable for future interpretation of graph metrics. Results indicate that graph metrics have characteristic forms when plotted against P that can be exploited for conservation management.

Darren Albert DeStefano

Chemotherapeutic Treatment Options to Manage Xylella fastidiosa in Shade Trees 

Xylella fastidiosa is a fastidious, xylem-limited, broad spectrum, bacterial plant pathogen native to the Americas, causing substantial economic losses to the viticulture, citrus, and shade tree industries. In shade trees the disease is manifested as a chronic late season leaf scorch largely confined to urban areas of southeastern North America. Proposed treatments include antibiotics and growth regulators. Recently paclobutrazol, a diastereomeric triazole with fungistatic and growth regulation properties has been associated with symptom remission. Investigation into direct interaction of paclobutrazol with X. fastidiosa show no significant reduction in growth at the manufacturers recommended dosage of 20 µg ml-1; however significant reductions in growth were observed at a dosage of 200 µg ml-1. Therefore high levels of paclobutrazol may have a direct effect on X. fastidiosa while other plant physiological effects induced by paclobutrazol merit investigation for association in symptom mitigation of X. fastidiosa.

Robert Edward Vaughan 

Agricultural Drainage Ditches: Soils and Implications for Phosphorus Transport and Retention 

Agricultural drainage ditches act as pathways for nutrients to local surface waters. Knowledge of ditch materials, the spatial variation and distribution of ditch soil phosphorus, is critical to effective ditch nutrient management strategies. Ditch materials from the University of Maryland Eastern Shore Research Farm in Princess Anne, Maryland were described and characterized using a pedological approach. The spatial variation of phosphorus was also investigated. The materials found within these ditches are natural soil bodies. Pedogenic processes operating in these soils include organic matter accumulation, structure formation, Fe oxidation and reduction, sulfuricization, sulfidization, and bioturbation. Soil phosphorus was well autocorrelated, and exhibited a high degree of spatial variation. Ditch soil phosphorus at depth ranged from 4 to 4882 mg kg-1 for total phosphorus, 4 to 4631 mg kg-1 for oxalate-extractable phosphorus, and 2 to 401 mg kg-1 for Mehlich-3 phosphorus. Future ditch management strategies should include a subsurface soils component.

Steven James McDonald 


Agrostis stolonifera and Lolium perenne are widely used turfgrass species grown on golf fairways, however, they are susceptible to dollar spot (Sclerotinia homoeocarpa) and gray leaf spot (Pyricularia grisea) diseases, respectively. Two field studies were conducted to assess: 1) the influence of two irrigation regimes and seven chemical treatments on dollar spot and gray leaf spot severity; and 2) the effects of two spray volumes (468 and 1020 L water ha-1), two fungicides (chlorothalonil and propiconazole) and three application timings (dew present or displaced and dry canopy) on dollar spot control. Dollar spot was more severe in A. stolonifera subjected to infrequent irrigation; whereas, gray leaf spot was more severe in frequently irrigated L. perenne. The plant growth regulator and wetting agent evaluated suppressed dollar spot, but they had no effect on gray leaf spot. Chlorothalonil was most effective when applied to a dry canopy in 468 L water ha-1.

Justin Tyler Pearce

Double-Cropped Soybean Response to Various Wheat Stubble Managements 

Varying responses to wheat (Triticum aestivum L.) stubble management preceding double-crop soybean [Glycine max (L.) Merr.] have been reported; however, little work has been done in the Mid-Atlantic region of the United States. The objectives of this study were to observe the effects of wheat stubble management (WSM) on physiological growth and yield characteristics for double-cropped glyphosate-resistant soybean, soil moisture retention and soil surface shading, monitor weed response characteristics, and to perform a simple economic analysis comparing the four WSM treatments. Soybean plant height, lowest pod height, and soil surface shading were greater in the 30 cm stubble treatment; however, there was no plant lodging or yield response to WSM, and soil moisture contents were unaffected due to the ample rainfall that was received during 2003 and 2004. As a result, 15 cm stubble with the straw removed via baling was found to be the most economically profitable treatment.

Matthew Dexter Stevens 

Sustainability of Cold-climate Strawberry Production Systems 

Three cold-climate strawberry (Fragaria xananassa Duch.) production systems, conventional matted row (CMR), advanced matted row (AMR), and cold-climate plasticulture (CCP) were compared for aspects of sustainability including environmental impacts, economic viability and public acceptance over a three year production cycle. As a result of higher total yields, CMR had the highest overall revenue and estimated net profit of any system. The CCP had the lowest observed yield but the largest fruit in year one. Reduced fruit size and yield in the second harvest season indicate the CCP system may not be suitable for perennial production. Both the CCP and AMR production systems were better than CMR in preventing soil, nitrogen and pesticide loss due to rain-induced runoff, and had higher N uptake than CMR. The CCP and AMR systems were preferred over CMR in a pick-your-own consumer preference evaluation. AMR and CCP represent potential sustainable alternatives to the CMR system.

Amy Neal

Utilizing Hybrid Poplar Trees to Phytoremediate Soils with Excess Phosphorus 

Phytoremediation, using plants to remove soil pollutants, has been suggested as a method to remove P from over-enriched soils. This research investigated the potential of utilizing hybrid poplar trees to remove excess P from soils associated with long-term poultry manure application. Hybrid poplar clones were planted in Snow Hill, MD, on three fields differing in previous poultry manure applications with Mehlich-3 soil-test P levels of 261, 478, and 982 mg P kg-1. During this two year study, soil P decreased on fields planted with hybrid poplar; the magnitude of the reduction was positively associated with initial soil-test P. Plant tissue P concentrations increased with soil P concentration. However, factors other than plant uptake were hypothesized to contribute to the soil-test P reductions. Results suggest that hybrid poplars have the potential to phytoremediate soils with excess P but that soil chemistry also impacts the fate of available P in the soil.

Rachel Esther Gilker 


Dairy farm size has increased in the United States, while the profit margin has decreased. An alternative to confined feeding dairy farming is management intensive grazing (MIG), a grass-based system relying on rotational grazing for most of the herd's dietary requirements. Previous research has measured high levels of nitrate leaching under MIG, citing the liquid nature and high nitrogen (N) content of urine. However, this research included heavy N fertilizer applications or was conducted on monolith lysimeters with artificial leaching processes and did not accurately represent mid-Atlantic MIG dairy farms. Phosphorus (P) losses have typically been attributed to runoff and erosion but are now being ascribed to leaching as well. To measure the magnitude of N and P losses to groundwater, we sampled shallow groundwater and pore water on one confined feeding and two MIG-based Maryland dairy farms between 2001 and 2004. Transects of nested piezometers and ceramic-tipped suction lysimeters were installed in two watersheds on each farm. Two streams running through two of the grazed watersheds were also sampled to measure the effects of grazing on surface water. For three years, groundwater and surface water samples were collected biweekly and pore water was collected when conditions made it possible. Samples were analyzed for inorganic N and dissolved reactive P and were digested for determination of dissolved organic N and P, pools previously not considered major sources of nutrient loss. Seasonal mean nitrate concentrations under the grazed watersheds remained below the EPA maximum contaminant load of 10 mg L-1 with only two exceptions on the grazed watersheds. Mean nitrate concentrations in the four grazed watersheds ranged from 3 to 7.44 mg L-1. Nitrogen losses were closely correlated to farm N surpluses. Groundwater P concentrations exceeded the EPA surface water critical levels in all six watersheds. Geologic factors, rather than dairy farm management, played a large role in P losses. In all watersheds, substantial pools of dissolved organic N and P were measured in groundwater. Low nitrate losses under MIG as well as the environmental advantages inherent in a grass-based system make grazing a viable Best Management Practice.

Shu-fei Lin


'Gala' and 'Fuji' are two high-quality apple (Malus domestica Borkh) cultivars. Their fruits mature and tree-ripen over a long period of time, and are resistant to pre-harvest drop. "Tree factor," a putative inhibitor of system 2 ethylene production is hypothesized to account for differences in ethylene production between attached and detached apple fruits. Three years of field data revealed two distinct patterns of maturation and ripening behavior in these two cultivars. 'Gala,' an early cultivar, demonstrated a typical positive "tree factor." Studies of the ripening pattern of 'Fuji' apple, which is a late-maturing cultivar, did not. 'Fuji' data were confounded by cold weather in the late fall. The natural progression of tree-ripening did not lead to the high concentrations of internal ethylene routinely measured in stored fruits. The stimulation of ethylene found in picked 'Gala' fruits ripened in the orchard might be explained by wounding stress coupled with a loss of nutrients and the water stress. Our alternative explanation for "tree factor" is the effect of continued termination of the phloem and xylem connection. The strength of the "tree factor" declined as 'Gala' fruit maturity progressed. Therefore, the "tree factor" tends to be more obvious in fruits with shorter growing period that mature during warm weather. To investigate differential gene expression that accompanies maturation and tree ripening, we used cDNA-AFLP (Amplified Fragment Length Polymorphism) to identify changes in transcript profiling during tree-ripening, and in the ripening of harvested fruits. Two hundred differentially-expressed transcript-derived fragments were isolated from 'Gala.' Ripening-related genes including those known to function in the key processes of defense and stress, cell wall degradation, pigment production and aroma biosynthesis were identified. Clones similar to housekeeping genes involved in protein biosynthesis and degradation, intracellular trafficking and sorting, cell structure and mobility, and metabolism-associated genes were also isolated. Expression patterns of these transcript-derived fragments were verified by using a different 'Gala' sample set on microarray and/or Northern blots. Our study supports the hypothesis that many ripening processes are under transcriptional control and that most of these differentially-expressed genes are highly conserved in fruits.

David Lee Hyten, Jr.,


Domestication, founder effects, and artificial selection can impact populations by reducing genome diversity and increasing the extent of linkage disequilibrium (LD). To understand the impact of these genetic bottlenecks and selection on sequence diversity and LD within soybean [Glycine max (L.) Merr.], 111 genes and three chromosomal regions located on linkage groups A2, G, and J were characterized in soybean. Four soybean populations were evaluated: 1) the wild ancestor of soybean (G. soja), 2) the population resulting from domestication (landraces), 3) Asian introductions from which North American cultivars were developed (ancestors), and 4) elite cultivars from the 1980's (elite). A total of 438 single nucleotide polymorphisms (SNPs) and 58 insertions-deletions were discovered within the 102 genes. Sequence diversity was lower than expected in G. soja with an overall theta equal to 0.00235, and was less than half that value (theta = 0.00115) in the landraces. Domestication eliminated most unique haplotypes with G. soja containing 240 unique haplotypes while the landraces only contained 42 unique haplotypes. The founder effect of the introduction of soybean to North America followed by intensive artificial selection, resulted in only a 30% decrease in nucleotide diversity. A total of 738 SNPs were discovered and genotyped in the four populations throughout three chromosomal regions. In G. soja LD did not extend past 100 kb while in the three cultivated soybean populations LD extended from 90 kb up to 600+ kb, most likely as a result of increased inbreeding and domestication. The three chromosomal regions varied in the extent of LD within the populations. G. soja is the greatest resource for unique alleles and may be best suited for fine mapping utilizing association analysis. The landraces do not contain much more variability than the elite cultivars but may have enough diversity to facilitate genetic improvement of elite cultivars. Finally, due to the extended levels of LD in the landraces and the elite cultivars, whole genome association analysis may be possible for the discovery of QTL.

Jennifer Theresa Renz 

Assessing evapotranspiration rates of a Mid-Atlantic red maple riparian wetland using sap flow sensors. 

Riparian forests are unique due to increased exposure of trees to winds and radiation and the subsequent effects on the quality and quantity of water discharge from the system. Since "edge effects" can enhance evapotranspiration (ET) of exposed trees, ET rates of a first-order red maple riparian wetland were assessed with thermal dissipation probes during the 2002 growing season to address: a) if edge trees transpire more water daily than interior trees, b) correlations among sap flow rates and energy balance-derived estimates, c) variations in ecosystem ET estimates based on 6 scaling variables, and d) diurnal correlations between maximum sap flow rates and streamflow losses. Results from this study indicate that: a) edge trees transpire more water daily than interior trees during early summer, b) choice of scaling variable affects estimation of ecosystem ET rates, and c) maximum sap flow rates correlate with streamflow losses diurnally under specific environmental conditions

David Slak 

The Establishment and Persistence of American Ginseng (Panax quinquefolius L.) in Maryland Forests. 

American ginseng (Panax quinquefolius L.) is a profitable non-timber forest product with the potential of improving the sustainability of Maryland forests. In order to determine factors affecting Maryland ginseng production, ginseng seeds and roots were planted in forests in Eastern, Central, and Western Maryland in plots amended with no treatment, lime, or gypsum. The response variables measured included soil nutrients and ginseng persisence and establishment. In general, soil lime treatments improved establishment at the Eastern but not the Central or Western sites. The gypsum soil treatments did not significantly affect populations. Establishment of American ginseng grown from seed ranked by site was Western&gt;Central&gt;Eastern. Conversely, root establishment was best at the Eastern site. Across sites, soil pH, Ca, Mg, and K were positively correlated with establishment and persistence. Thus, American ginseng was grown throughout Maryland and ginseng production was enhanced by lime addition at the Eastern site.

Shawn Thomas Lucas


A KMnO4 oxidation method for estimating labile soil C (CL) was evaluated for use in a soil testing mode to identify soils where soil quality and productivity is likely or unlikely to respond positively to increased levels of CL. Four sets of paired fields of the same soil series (within each set) but contrasting soil management history (continuous cropping vs. long-term sod) were studied. Fields with sod history initially tested higher in total soil C and CL than fields with cropped management history. Within each field two treatments (winter rye cover crop or no cover crop) were applied in each of four blocks. Crop and soil functional responses to rye, when significant, were higher in fields that initially tested lower in CL indicating that the KMnO4 method used has some predictive value as a soil test. The method could be used in field testing kits for evaluation of soil C.


Jackson Fisher 

Spatial Distribution of Surface Soil Moisture under a Cornfield 

Autocorrelation within surface soil moisture (SSM) data may be used to produce high-resolution spatial maps of SSM from point samples. The objective of this study was to characterize the temporal and spatial properties of SSM (0-5 cm) in a Beltsville, MD cornfield using capacitance probes. The range of spatial autocorrelation was approximately 10 m and the highest sill values were found at water contents (theta) between 20-27%. Nugget values represented a significant portion of the total variance (up to 50% for theta > 20% and 73% for theta < 12%). The patterns of SSM under wet conditions exhibited large, continuous polygons while drier conditions resulted in smaller, discreet regions. Early season (< 60 days) Auto-Regressive Moving-Average (ARMA) forecasts of SSM plotted against observed data resulted in R2 values from 0.15-0.26, while late season (>80 days) forecasts improved to 0.46-0.65. Forecasts were improved by autoregressive coefficients and additional SSM datasets.

Shengchum Wang

Efficiency and Ecological Risks of Reducing Soil pH during Thlaspi caerulescens Phytoextraction of Cadmium and Zinc 

The major aims of this research were to determine whether reducing soil pH can enhance phytoextraction and to examine the ecological risks of reducing pH. Two soils differing in Cd and Zn concentrations were used and adjusted to 5 or 6 different pH levels ranging from 7.27 to 4.74 and seeded with a hyperaccumulator of Cd and Zn, Thlaspi caerulescens. Plants were harvested after six months, the pH were restored to above 6.5, incubated for 6 months. Soils were analyzed for biological activities and microbial population changes after both pH adjustments. Reducing pH significantly (p=0.05) enhanced plant metal uptake. For the high metal soil, plant grew best at the lowest pH treatment (4.74) and the highest metal concentration was at the second lowest pH treatment (5.27). For the low metal soil, due to low pH induced Al and Mn toxicity, plant growth and metal uptake were highest at the intermediate pH level (6.07). Metal sequential extraction results further verified that reducing pH redistributed Cd and Zn among five fractions. The most soluble metal form (F1) was greatly increased. In addition, T. caerulescens was able to differentially utilize Cd in all 5 fractions while it could only access Zn from the F1 and F2 pools. Reducing soil pH significantly reduced a number of soil biological activities and shifted the community structure at different levels. Generally, soil biological activities were more sensitive than soil microbial populations to pH change. Good indicators of soil pH status were acid phosphatase activity, alkaline phosphatase activity, acid to alkaline phosphatase activity ratio, arylsulphatase, nitrification potential, soil microbial biomass C and N, and population of rhizobium. After raising pH to &gt; 6.5, negatively impacted soil parameters were partially restored to original levels. Soil biological activities showed lower recovery than soil microbial populations. The threshold pHs were 6.1 and 5.3 for low and high metal soils, respectively. Above this value, most soil biological activities and all microbial populations returned to background levels within a short period.

John Kaminshki 

Biology of Ophiosphaerella agrostis, epidemiology of dead spot, and a molecular description of the pathogen 

Ophiosphaerella agrostis is a newly described pathogen that incites dead spot disease of creeping bentgrass (Agrostis stolonifera) putting greens throughout the eastern United States. The objectives of this research project were to: 1) monitor environmental conditions and develop a predictive model for disease progress and pathogen dispersal under field conditions; 2) determine the effect of various fertilizers on dead spot recovery in bentgrass; and 3) develop molecular methods to diagnoses the disease and determine genetic variation among O. agrostis isolates. Field studies showed that the appearance of dead spot infection centers was influenced predominantly by air (greater than or equal to 18 degrees Centigrade) and soil (greater than or equal to 20 degrees Centigrade) temperature, but other factors including low relative humidity (less than or equal to 80%), shortened periods of leaf wetness (less than or equal to 14 hours), and high levels of solar radiation (greater than or equal to 230 W m to the minus 2) were associated with the development of dead spot epidemics. Patch diameter of O. agrostis infection centers and pseudothecia production generally increased at a linear rate between mid-June and early to mid-August. In a growth chamber study, ascospores were released from pseudothecia following a sharp decrease in relative humidity. Field studies revealed that ascospore release occurred primarily at dawn and dusk or during precipitation events. During precipitation events, ascospores may be forcefully discharged during the entire event, but most ascospores are released within the first 10 hours after precipitation begins. O. agrostis successfully over-wintered in bentgrass leaf sheaths, crowns, roots, and stolons, but little or no reactivation of the disease occurred in the second year. Plots treated with ammonium sulfate and isobutylidene diurea were among the fastest and slowest to recover from dead spot, respectively. In the second year (2003), dead spot recurred in plots treated since 2002 with KNO3, Ca(NO3)2, urea, and a complete fertilizer (20-20-20), but disease symptoms did not recur in plots receiving ammonium sulfate. Species-specific primers capable of detecting O. agrostis at very low concentrations (5 pg DNA) were developed and can be used to assist in diagnosing dead spot. Amplified fragment length polymorphism (AFLP) DNA fingerprinting resulted in placement of isolates (n=77) into three distinct clades that were greater than or equal to 69% similar.

Carinne A. Raymond 


Consumer demand has prompted an increase in geranium breeding efforts to produce new cultivars each season. It is hypothesized that the breeding for unique morphological traits has inadvertently resulted in changing the plant's ability to competitively take up nutrients. Under certain conditions, nutrient uptake of these novelty cultivars is less efficient, possibly caused by the influence of the geranium itself. Information collected from the container media is a good indicator of the container nutritional status and can be used as a diagnostic tool for early identification of nutritional problems and prevent plant loss. Severe nutrient deficiencies and toxicities have been associated with plants fertigated with low alkalinity water, suggesting that an unsteady pH in the rhizosphere coupled with low buffering capacity of irrigation water may cause preferential nutrient uptake. Maintaining a media pH that optimizes nutrient solubility while preventing interactions or precipitation is the goal for ensuring proper plant nutrition. Three experiments were performed to address the following objectives: 1.) Evaluate the effects of the geranium cultivar and class on the container media. 2.) Determine if media type affects nutrient availability and uptake by geraniums. 3.) Identify if preferential nutrient uptake occurs in response to changing pH and water alkalinity levels in the container media. Results indicate that a significant reduction in media pH occurs for zonal and ivy geraniums during a specific stage of growth and that the effects of pH and water alkalinity on nutrient uptake and are highly specific to the nutrient tested and the media type. Significant interactions between water alkalinity and pH contributed to preferential uptake of several of the tested nutrients especially at low water alkalinities. Overall, the differences in uptake were in most cases specific to cultivar, the stage of growth and nutrient tested and should be considered when determining optimal fertility requirements for specific geranium cultivars.

Katherine Diane Salmon 


Low phytic acid (LPA) is a mutation causing phosphorus to be stored as unbound phosphorus in the seed. LPA mutants show a high inorganic phosphorus (HIP) phenotype. Previous studies had indicated that LPA might be linked to the myo-inositol (3) phosphate synthase (MIPS) gene; this research attempted to associate a soybean HIP mutant with the MIPS gene. The parental and the F2 genotypes were tested in four ways: 1) SNP detection using the LCR protocol; 2) polymorphism detection with PCR; 3) high inorganic phosphorus (HIP) phenotype detection; and 4) oil and protein concentration. The two parental genotypes could not be differentiated in the LCR study. A PCR-based polymorphism was heritable in the F2 genotypes. HIP assay indicated multiple genes control the LPA mutant. A polymorphism was associated to the HIP phenotype. The three types of HIP phenotypes were not statistically different in oil and protein concentrations allowing implementation into a breeding program.

 Carol Sue Gordon

Soil Properties and Native Plant Communities in a Kansas Prairie 

I hypothesized that the relative proportion of grasses and legumes in native prairie communities are associated with physical and chemical soil properties. In a greenhouse study, I determined species responses to differences in soils ex situ by individually growing three grasses, two legumes, and two composites in soils from four sites on a never-plowed prairie at The Land Institute in Saline County, KS. The highest organic matter (OM) soil produced the highest plant dry matter for five of the species. In a field study, I measured 20 soil properties in 24 quadrats (0.5 m2) with high, low, or no legume cover on the same four sites. After incubation, NH4 in subsurface soils was lower for high legume cover suggesting higher nitrification. Discriminant multivariate analysis showed the ratio, active C as a percent of total C, and percent OM were the most closely associated surface soil variables with percent legume cover.

Tonya Suzanne Mallozzi

Assessment of select isolates of Trichoderma virens as a potential biocontrol against Meloidogyne incognita 

Three isolates of the soil-dwelling fungal organism, Trichoderma virens (Miller, Giddens and Foster) von Arx., were studied as potential biocontrols for the management of root-knot nematode (RKN) on bell pepper (Capsicum annuum L.). The study was conducted within the Moisture Replacement System (MRS), which was concurrently evaluated for its ability to serve as a culture system for Meloidogyne incognita (Kofoid and White) Chitwood and as an environment supportive of the growth and maintenance of Trichoderma isolates for biocontrol studies of this nature. Trichoderma isolates selected for study did not suppress populations of RKN on bell pepper under the conditions of this study. A review of the literature provided a multitude of complexities potentially contributing to the final results obtained. Investigation into these various complexities with the incorporation of the MRS will help to fully ascertain Trichoderma's potential as a biocontrol and perhaps reveal viable alternatives in the management of RKN.

Eva Claire Creighton Synkowski

Breeding Considerations for Improving Cadmium and Zinc Hyperaccumulation in Two Thlaspi caerulescens Populations 

Cadmium is the second most widespread soil metal contaminant in the world and it has been suggested that phytoremediation using hyperaccumulator plants could be used to effectively remove harmful levels of soil metals. This research was conducted to provide basic information necessary for developing a breeding program to improve the phytoremediation potential of Thlaspi caerulescens, a promising hyperaccumulator plant. By determining the genetic structure of the source populations and estimating the heritability of traits of interest, gain from selection was predicted. Bulk segregrant analysis of DNA polymorphisms was used to identify markers linked to cadmium hyperaccumulation. DNA markers would reduce time and expense of selecting superior genotypes. However, confounding effects from marker technology, experimental design, and sample size reduced the potential for implementing the detected markers in a breeding program. Future experiments may still detect markers for hyperaccumulation and the T. caerulescens populations studied are valuable for phytoremediation application.

Andrew George Ristvey 


Water quality remains a predominant issue within the Chesapeake Bay watershed, and nutrient loading continues to undermine the progressive recovery of this ecosystem. Until recently, the ornamental plant industry has had little information to develop better management practices to increase the efficiency of water and nutrient applications. This research used an integrated approach to examine container- production systems, to develop recommendations to increase nutrient uptake efficiency and reduce runoff. A 40-month field study examined the effects of various cultural practices on irrigation and nutrient uptake efficiencies. Under cyclic scheduling, drip irrigation applied 3 to 4.5 times less water than overhead irrigation and had significantly less runoff when plants were spaced at low densities. While drip irrigation is significantly more efficient, overhead irrigation is more practical and economically feasible for most small container-nursery stock. Time Domain Reflectometry (TDR) was examined as an alternative to cyclic scheduling and when used with overhead irrigation, water applications were half that of cyclic irrigation scheduling. . This research simultaneously documented nitrogen (N) and phosphorus (P) dynamics by examining nutrient applications, uptake and leaching over the forty months. In most cases, N and P uptake efficiency and runoff was negatively affected by overhead irrigation, particularly when soluble nutrients were applied via fertigation and at low plant densities. Nitrogen and P efficiencies ranged between 10 and 30% and were dependent upon methods of irrigation and fertilization, plant density and water use. The use of both drip and TDR-scheduled overhead irrigation reduced nutrient runoff to half that of the overhead irrigation program Intensive spring nutrient uptake studies showed that N influences the total growth of Rhododendron (azalea) and P uptake is a function of P fertilization rate and growth, influenced by N rate. Moderate N rates maintained optimal growth, while total P was only required at 1/20 of this N rate. Periodicity in nutrient uptake suggests seasonal timing of fertilizers may increase N and P uptake efficiency. Novel management strategies in the area of irrigation, fertilization, and cultural practices should be adopted by the ornamental industry to improve upon low efficiencies and reduce nutrient pollution in our watersheds.

Karen Lynn Castenson 

Hydromorphology of Piedmont Floodplain Soils

Alluvial soils situated on middle locations along Mid-Atlantic Piedmont floodplains lack characteristic redoximorphic features that allow them to meet a current field indicator of hydric soil. Although these soils appear to be located in wetlands based on their hydrologic, vegetative, and electrochemical status; there is no hydric soil indicator that accurately includes soils on these landscapes. Two research sites in Maryland and one in Delaware were instrumented along a hydrosequence. Depth to water table, redox potential, and soil temperature were measured. Redox potential measurements of the hydric and possible hydric soil conclude that Fe(III) is predicted to be reduced to Fe(II) for a significant period of time during the growing season. Based on data collected over three years, the possible hydric soil was confirmed hydric. An alternate hydric soil indicator has been proposed for these landscapes.


John Stuart Wah 

The Origin and Pedogenic History of Quaternary Silts on the Delmarva Peninsula in Maryland 

Soils formed in Quaternary age silts are widespread on the Delmarva Peninsula in Maryland. The origin, mode of transportation and deposition, and age of the sediments in which these soils formed have long been debated and are important to understanding climate change and to investigations of the prehistory of the Delmarva. This study was undertaken in an effort to resolve the issue of the origin of parent sediments, to examine the pedogenic history of the soils, and to gain insight into the paleoclimate of the region. Thirty nine profiles were described and sampled in two north-south transects on the upland and the broad terrace along the Chesapeake Bay on Maryland's Eastern Shore. Laboratory analyses included determination of particle size distribution, determination of Zr, Ti, Ca, and K contents of coarse silts, mineralogical analysis, and the examination of biogenic opal. The silty mantle overlying sands ranged in thickness from 150 cm to less than 50 cm, with considerable variation across the study area. Textures of this mantle were silt loam and silty clay loam with 53 to 94 percent clay-free silt and a mean clay-free particle size of 41 mm. The Zr content of the silts was uniform within profiles and across the study area while that of Ti, Ca, and K varied. Mineralogy of the silts was homogeneous across the study area. There were no features diagnostic of either fluvial/estuarine or eolian processes in the silt deposit. Minimal coarse fragments and no stratification were observed. Low chroma matrix colors of soils reflected modern drainage conditions rather than a reducing depositional environment. Pedological development argued for relatively young soils (&lt; 30,000 years) and archaeological materials from surface horizons buried by the silts dated the onset of deposition to the end of the Pleistocene (approximately 10,500 14C years BP). The youthfulness of the silts precluded them from having been deposited during the Sangamon transgression, which occurred no more recently than 82,000 years BP, and proved unequivocally that the silts are loess. Buried paleosols were indicative of the landscape stability prior to loess deposition while phytoliths reflected a climate shift

 Mbisin Diagne 

Management of White Rust (Caused by Albugo Occidentalis) Of Spinach and Its Impact on the NonTarget Invertebrate Community 

White rust, caused by the oomycete Albugo occidentalis, is a major foliar disease of spinach (Spinacia oleracea). Favorable environmental conditions are required for its initiation and development. A modified version of a weather-based spray advisory program was evaluated using chemicals with different modes of action. Entomopathogenic fungi may infect Myzus persicae, a major pest of spinach. The nontarget effects of chemicals used in the management of white rust on entomopathogenic fungi and on the invertebrate community were also investigated. Both acibenzolar-S-methyl initiated at the second true leaf stage and pyraclostrobin applied according to the advisory program and weekly, reduced disease incidence compared to untreated plots. Naiad sprayed weekly reduced the percentage of aphid infested leaves, however no entomopathogenic fungi were isolated. All three chemicals caused population increases in predatory mites and phytophageous thrips. Actigard and Naiad caused increases in oribatid mites and beetle larvae populations

Kristine Ann Nichols 


Glomalin is an insoluble glycoprotein produced by hyphae of arbuscular mycorrhizal (AM) fungi. It is resistant to degradation and is found in large amounts in soil. Classical operationally defined extracts of soil organic matter include a large proteinaceous fraction. Therefore, clarification of glomalin as a separate fraction of extractable soil organic matter (SOM) is needed. Proof that glomalin accumulates over long periods of time has not been attempted. The overall hypothesis tested for this dissertation is that AM fungi are the source of an abundant, unique and important SOM component. The quantity of glomalin in soils was compared with particulate organic matter (POM), glomalin, humic acid (HA), and fulvic acid (FA) which were sequentially extracted from 5 8 undisturbed U.S. soils, aggregates and agriculturally managed soils that differed in tillage, crop rotation, and/or fertilizer amendment. Each fraction was extracted with the appropriate procedure: glomalin in pH 8.0 citrate at 121C, POM by floatation in NaCl solution, and HA and FA in NaOH with acidic separation. Organic matter fractions were evaluated for total and immunoreactive protein and/or gravimetric and C weights. Percentages of C, N and H were used to characterize each fraction. Glomalin structure was examined by proton nuclear magnetic resonance (1H NMR), removal of iron and separation of amino acid and carbohydrate groups. Glomalin accumulation in pot cultures was assessed at 14-week intervals in a 294-day experiment. Glomalin was unique in protein, C, H, and N contents compared with HA, FA and POM. Glomalin contributed ca. 20% of soil organic carbon. A recalcitrant glomalin pool was discovered that might have a functional role in water-stability of aggregates. 1H NMR spectra of glomalin were unique compared with HA spectra. Extracted glomalin had tightly bound iron, organic matter, amino acids and carbohydrates. Sustainable agricultural management practices reduced tillage, increased crop diversity, and reduced synthetic amendments increased aggregate stability of bulk soil and glomalin and POM concentrations. Glomalin production under controlled conditions was affected by irradiance. These results provide evidence that glomalin is a separate and unique fraction of SOM and is important in terrestrial carbon sequestration and sustainable agricultural practices.

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