ABSTRACT

Abstract

Arctic landscapes are changing rapidly. The "greening" and "shrubification" of the Arctic drive climate feedbacks (via albedo and energy exchange) as well as affecting human activities directly. Vegetation change, however, is driven belowground by nutrient availability, a result of microbial feedbacks that also have independent effects on the climate system (e.g. CO2 and CH4 emissions). The microbial system, therefore, plays a key role in regulating the functioning of the overall Arctic System. As organisms migrate and spread across the Arctic, the processes they regulate migrate with them. Predicting changes in the pattern of tundra biogeochemistry therefore requires understanding the factors that regulate the distribution and functioning of key groups of microbes. Are bacteria and fungi regulated simply by the chemical substrates available to them, and thus by plant distribution? Or alternatively, are microbes independently regulated by the challenges of tolerating the freezing conditions of winter? What are microbial adaptations to low temperature, and what are their ecological consequences? These are interesting questions for basic microbial ecology, but are also important in the context of the changing Arctic. The core hypotheses of this project are: 1) the distribution of specific microbial groups is controlled primarily by plant community composition, but 2) the challenge of acclimating to winter requires changes in membrane composition, cryoprotectants, and freeze-tolerance proteins that involve physiological costs to microbes that have important implications for overall ecosystem function. Hypotheses will be tested by analyzing patterns of microbial distribution and physiology across toposequences in Alaska (low Arctic) and Greenland (high Arctic), capturing latitude and plant community variation. Seasonal changes (pre- and post-freeze, pre- and post-thaw) will be assessed by using clone library and quantitative genetic analyses (QPCR) to evaluate microbial community composition. Microbial membrane chemistry (phospholipids) and cryoprotectants (amino acids, trehalose, polyols) will be assessed by chemical analyses. Shifts in protein production patterns, including anti-freeze proteins, chaperones, and others will be assessed using proteomic techniques. This work will be supported by laboratory studies evaluating specific aspects of freezing stress: rate, temperature, and duration. It will be integrated with other studies on pan-Arctic microbial population dynamics by collaboration with the ICSU MERGE network. This will be the first ever study on how stress physiology regulates microbial distributions.

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