Modeling Plant-Microbe Interactions as Carbon Dioxide and Temperature Rise

The Science

PFLOTRAN, a reactive transport model, was used to test how elevated temperature and carbon dioxide (CO₂) alter the connections between plants, water, and soil processes in a salt marsh. Daily cycles associated with tides and photosynthesis were included in the model, and the impacts of climate stress were applied directly to the soils as well as indirectly through plant responses. Including daily cycles significantly influenced rate estimates, resulting in a higher or lower gas emission than anticipated depending on the time of day. The indirect effects mediated through plant responses were more important in regulating redox cycling than the direct influence of stress on soils.

The Impact

Earth system models typically do not represent the dynamics between plants, water, and soil with the spatiotemporal resolution needed to fully characterize coastal systems. Pore-scale models have a higher resolution but may not include feedbacks between the system components that regulate climate responses. This intermediate scale–model study shows the importance of incorporating daily cycles to better estimate redox processes and how representation of the connections between plants, microbes, and water can improve predictive capacity.

Summary

Coastal ecosystems have been largely ignored in Earth system models but are crucial zones for carbon and nutrient processing. Interactions between water, microbes, soil, sediments, and vegetation are important for mechanistic representation of coastal processes. To investigate the role of these feedbacks, researchers used PFLOTRAN to simulate coastal processes. PFLOTRAN representation included redox reactions important for coastal ecosystems and a simplified representation of vegetation dynamics. The goal was to incorporate oxygen flux, salinity, pH, sulfur cycling, methane production, and plant-mediated transport of gases and tidal flux. Depth-resolved biogeochemical soil profiles were created for the salt marsh habitat using porewater profiles and incubation data for model calibration and evaluation. The updated representation was used to simulate direct and indirect effects of elevated CO₂ and temperature on subsurface biogeochemical cycling.

Increasing CO₂ temperature or concentration in the model did not fully reproduce observed changes in the porewater profile. However, including plant or microbial responses to these stressors was more accurate in representing porewater concentrations. This result indicates the importance of characterizing tightly coupled vegetation-subsurface processes for developing predictive understanding and the need for measuring plant-soil interactions on the same time scale to understand how hotspots or moments are generated.

Principal Investigator

J. Patrick Megonigal
Smithsonian Environmental Research Center
[email protected]

Co-Principal Investigator

Genevieve Noyce
Smithsonian Environmental Research Center
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

Funding for this project was provided by the U.S. Department of Energy, Office of Science, Biological and Environmental Research (BER) program, Environmental System Science (ESS) program under award numbers DE-SC0014413, DE-SC0019110, DE-SC0021131, and DE-SC0021112. Additional support was provided by Coastal Observations, Mechanisms, and Predictions Across Systems and Scales—Field, Measurements, and Experiments (COMPASS-FME), a multi-institutional project supported by BER as part of ESS, the Smithsonian Institution, and the National Science Foundation Long Term Research in Environmental Biology Program (DEB-0950080, DEB-1457100, DEB-1557009, DEB-2051343).

Related Links

• ESS-DIVE simulation archive
• SMARTX information
• GENX information

References