Collaborative Research: Microbial processes and carbon transformation in the thawing permafrost

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As a result of global warming, arctic ecosystems have reached a ‘new normal’ characterized by the loss of sea ice, retreating glaciers, and the beginning of widespread permafrost thaw. Permafrost (i.e., permanently frozen soil) contains an enormous amount of carbon, much of it in the form of detrital plant material. Subzero temperatures have protected this plant-derived carbon from microbial decomposition. Warming thaw removes this protection, exposing permafrost carbon to the action of microbial communities that will degrade it and ‘breathe’ globally significant amounts of carbon dioxide and methane (greenhouse gases) into the atmosphere. This release of permafrost carbon into the atmosphere could lead to even faster and greater climate change. Details of how this will play out are not well understood. The goal of this research is to understand how microbial communities function and degrade carbon during permafrost thaw. To achieve this goal, thaw will be simulated by transplanting permafrost into soil that overlays the permafrost and thaws annually during the summer months. Samples will be harvested at multiple time scales (weeks, months, and years). Microbial communities and soil carbon chemistry will be evaluated before and after transplantation to determine how communities change, function, and degrade carbon during thaw. The knowledge that will be generated by this research project is critically important to understanding how greenhouse gas production from thawing permafrost will contribute to future climate change. In addition to training a graduate student and postdoctoral researcher the project will also implement a novel "adopt a microbe" program as part of an undergraduate lab course. Estimates are that permafrost contains 25-50% of the total global soil carbon pool. As a result of global warming, up to 40% of northern latitude permafrost may disappear due to thaw by the end of the century. Permafrost thaw will unlock previously frozen carbon making it amenable to microbial community decomposition. Millennia-old organic matter will get converted to CO2 and CH4. The resulting production of globally significant quantities of CO2 and CH4 is likely to cause a positive feedback loop amplifying the effects of climate change. The overarching goal of this research is to more precisely determine the magnitude of this microbe-mediated feedback loop through understanding the rules governing microbial community composition, function, and carbon turnover in the thawing permafrost. To address this a series of novel, in situ thaw experiments will be performed. Permafrost of different ages (from the Holocene and Pleistocene) will be transplanted into the active layer (soil overlaying the permafrost that freezes and thaws annually) to simulate thaw. Prior to transplantation, soils will be sterilized and then inoculated with microbial communities from the active layer, from permafrost of different ages, or from a combination of communities and then sampled at different time intervals. Community structure, (taxonomic marker genes), functional potential (metagenomes), function (metatranscriptomes), and soil chemistry (FT-ICR MS, physicochemical measurements) will be evaluated. The outcome of this research will be an integrated conceptual model that relates community assembly and function to carbon turnover during thaw at multiple time scales. The project will include training in microbial ecosystem ecology research at the undergraduate, graduate and postdoctoral levels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.