College of Agriculture & Natural Resources
Plant Science & Landscape Architecture

Dr. Pat Megonigal: Climate change and soil carbon sequestration in wetland ecosystems

PSLA Lecture Series: Dr. Pat Megonigal
Figure 1. Soil organic matter-derived CO2 flux from unplanted and planted mesocosms at three different elevations relative to the reference marsh platform, low (-15 cm), mid (0 cm), and high (+20 cm), in 2012 and 2013.Significant differences (P < 0.05) ar

On Thursday, 17 March 2017, Dr. Pat Megonigal presented his research on plant-microbe interactions and greenhouse gas (GHG) budgets in tidal wetlands and other ecosystems to the Department of Plant Science and Landscape Architecture. Dr. Megonigal is an ecosystem ecologist at the Smithsonian Environmental Research Center (SERC) in Edgewater, Maryland and the lead investigator at the Global Change Research Wetland, the longest running climate change experiment in the world. During the seminar, Dr. Megonigal presented several of his experiments on plant-microbe carbon cycling in response to changing climate conditions such as elevated atmospheric carbon dioxide (CO2) concentrations, sea level rise, and nitrogen pollution. Specifically, he focused on the priming response in these systems in wetlands. During priming, soil organic carbon (SOC) is depleted due to increased supply of labile organic carbon. The priming effect in wetlands is induced by a combination of oxygen and new organic delivered to soil microbes through plant roots (Mueller et al., 2016). Simulating three flooding frequencies (above, below, and at current sea level) revealed increased plant biomass increases carbon emissions from the system (Figure 1). By partitioning carbon isotopes from plant and microbial respiration, Dr. Megonigal showed that these emissions were largely due to enhanced microbial respiration. From additional experiments and meta-analysis, he also found that elevated atmospheric CO2 concentrations increased microbial methane emissions in wetland systems. As a GHG, methane is roughly 45 times more potent than CO2 over a period of 100 years and causes a positive feedback loop by amplifying the effects of radiative forcing (Neubauer and Megonigal, 2015). From his presentation, it is clear that Dr. Megonigal has been tackling complex systems with many unknowns in their carbon cycling. This research can potentially have major implications for accurately assessing GHG emissions and global warming potential across ecosystems.

References:

Neubauer, SC and JP Megonigal (2015). Moving beyond global warming potentials to quantify the climatic role of ecosystems. Ecosystems 18:1000-1013. doi: 10.1007/s10021-015-9879-4

Mueller, P., Jensen, K., Megonigal, J.P., 2016. Plants mediate soil organic matter decomposition in response to sea level rise. Glob. Chang. Biol. 22, 404–414. doi:10.1111/gcb.13082

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