Warming and drying effects on tundra carbon balance

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Changes in permafrost carbon (C) storage are expected to be one of the most important and rapid feedbacks from terrestrial ecosystems to atmospheric CO2 concentrations. If the availability of permafrost C increases in a warmer and drier climate, as predicted for the study region, these systems may switch from a C sink to source and act as a significant positive feedback to global climate change. The objective of this research is to determine how temperature and moisture affect ecosystem C balance in an upland tundra ecosystem. This work will be conducted within the Carbon in Permafrost Experimental Heating Research project, a deep-soil and ecosystem warming experiment initiated in 2008, which was expanded in 2011 to include a water table manipulation treatment. The research will test the hypothesis that warming and drying will increase decomposition of soil C and decrease plant C uptake, leading to significant ecosystem C losses. This hypothesis will be tested through measurements of ecosystem CO2 fluxes, respiration source partitioning, plant productivity, and ecosystem nutrient dynamics. This work will provide critical information about climate change effects on belowground productivity and winter respiration. These two processes contribute significantly to tundra C balance but their responses to warming and drying are not yet quantified. Estimating the full breadth of ecosystem C responses is critical for understanding how changes in permafrost ecosystems will feedback to global climate.This proposed research will provide essential information on both the magnitude and drivers of climate change impacts on tundra C balance, and will link biological carbon cycle research with permafrost research in the physical sciences. In addition, this project will bridge a gap between ecology research and geochemistry through the extensive use of radiocarbon to detect the sources of respired CO2. The research will be conducted in the discontinuous permafrost zone, in an area of Alaska where permafrost thaw and thermokarst have been occurring over the past several decades, and where permafrost temperatures are perched near the point of thaw. Ecosystem changes in this region serve as an indicator of future shifts that are expected with degrading permafrost at higher latitudes, making this research highly relevant to changes occurring across the Arctic as a whole.This work will have broad impacts on the scientific community and general public because it brings together important issues in the global environment and raises awareness of the connection between northern ecosystem dynamics and the global climate system. The proposed project will provide training opportunities for one postdoctoral researcher and a diverse group of undergraduate students, and will be widely disseminated to the scientific community through timely publication of results, presentations at national meetings and involvement with scientific networks. This project will enhance scientific understanding through continued work by the PIs with education centers, the local community and in particular, with teachers and outreach coordinators.