Permafrost thaw as a framework for understanding plant-microbial interactions and terrestrial feedbacks to climate

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Half of Canadian land sits on permafrost, a layer of frozen soil, water, and rock.  We are a permafrost nation.  Northern Canada is also one of the most rapidly warming regions on Earth, and the stable frozen ground that has fundamentally shaped ecosystems, infrastructure, and resources across the north is thawing at unprecedented rates. Thawing permafrost provides new sources of energy for microbes, which in turn release carbon dioxide and methane to the atmosphere that contribute further to the greenhouse effect.  Known as the "permafrost carbon feedback", this cycle is one of the most likely positive feedbacks from land to the atmosphere with warming. However, the fate of permafrost carbon release as greenhouse gases depends on several key factors, including 1) whether thawing soils become flooded, which could reduce the activity of microbes, 2) whether thawing permafrost creates nutrient-rich conditions, which could stimulate microbial activity, and 3) whether increases in plant growth in response to thaw can help to offset permafrost carbon release. To address these issues, the proposed research will develop a mechanistic understanding of how plants and microbes compete for nutrients under aerobic and anaerobic thaw trajectories in the Northwest Territories and Alaska, two regions where permafrost is experiencing widespread thaw. The research will measure changes in nitrogen and phosphorus availability with permafrost thaw, and the consequences of soil nutrient enrichment on plant and microbial processes. Experimental studies that examine plant and microbial processes in real time will be complemented by a gradient approach, where a space-for-time substitution will be used to examine consequences of thaw on time-scales of 100s to 1000s of years. This research will inform science-based evidence promoting effective environmental regulation, land and water management, and resource development in the face of a warming climate and dynamic permafrost conditions throughout the North.