Coupled Long-Term Experiment and Model Investigation of the Differential Response of Plants and Soil Microbes in a Changing Permafrost Tundra Ecosystem. DOE, 2019-2022 (Co-PI, PI: Ted Schuur, Northern Arizona University)

The goal of this project is to address the following overarching question: How does the response of plants and soil microbes to changing environmental conditions affect permafrost ecosystem carbon balance over decadal timescales? We hypothesize that soil microbial communities will respond rapidly to environmental changes associated with permafrost thaw. This will result in the decomposition of old soil carbon that has been stored in these ecosystems due to cold temperatures. However, the trajectory of thawed permafrost soils into wetter and drier alternate states due to ground subsidence will determine whether soil saturation can continue to protect soil organic matter, as well the proportion of carbon dioxide and methane that is released to the atmosphere. Based on our latest results, we also hypothesize that changes in surface hydrology and thaw increases lateral carbon loss that can bypass the local microbial community, and that this pathway is significant in magnitude relative to direct atmospheric losses. Plant carbon uptake is expected to in part offset soil carbon losses, but this dynamic will change on a longer timescales (decades) as compared to the timescale of change for the microbial community. The plant response will be more limited than that of microbes especially where soils are dry. The slower successional dynamics of the plant community will cause greater time lags in potential long-term ecosystem carbon gain (after the initial ecosystem response phase), and also will be affected by the hydrologic change that exports nutrients and leads to the drier and wetter alternate states.