Predicting permafrost microbial community responses to thaw based on pre-thaw ecosystem characteristics

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Permafrost environments are among the most important carbon reservoirs on Earth. Sub-zero temperatures isolate permafrost microbial communities from overlying active layer processes, and protect permafrost carbon stores from microbial transformations. However, climate warming is increasing the rate and extent of permafrost thaw, increasing organic carbon bioavailability and carbon metabolism rates. These changes will liberate vast carbon stocks as carbon dioxide and methane, increasing positive feedbacks on climate warming. The rate and magnitude of these changes are dependent on microbial processes, influenced by the ecological processes that govern microbial community dynamics. At the landscape level, permafrost communities are shaped by homogeneous selection, which drives communities to look more similar as a result of shared selective pressures of the permafrost environment. However, permafrost microbial communities can vary over short spatial scales, influenced primarily by dispersal limitation which limits mixing of permafrost microbial communities. This suggests that, as dispersal constraints are relieved, biological and physicochemical characteristics of the overlying soils may become important drivers of microbial community structure and function in newly thawed permafrost. If so, variable selection will become a dominant ecological process, driving community variation in response to variable environmental conditions, and contemporary spatial patterns of biological communities in soils overlying permafrost will be good predictors of post--thaw community characteristics and process rates. However, no studies have examined patterns of permafrost microbial communities along with active layer soil communities over large spatial scales or attempted to model how interactions between permafrost and overlying soils will influence community structure and function at these scales as permafrost thaws. The objective of the proposed research is to improve understanding of the ecological processes influencing microbial distributions in permafrost and active layer soils across Canada's northern environments, and to use this knowledge to predict how these ecosystems will respond to permafrost thaw. The proposed research will investigate the following questions: Q1) Can patterns of active layer and permafrost microbial community composition be explained by environmental variation across Arctic and Subarctic landscapes? Q2) To what degree do characteristics of the pre--thaw permafrost microbial community influence responses to permafrost thaw? Q3) Can aspects of the pre-thaw environment be used to predict post--thaw microbial community function and carbon cycling dynamics? This work will improve understanding of the microbial diversity of active layer and permafrost soils across northern Canada, the ecological processes shaping these communities, and their potential responses to the accelerated warming of Canada's Arctic.