Collaborative proposal: Coupled biological and photochemical degradation of dissolved organic carbon in the Arctic
Overview: The thawing of organic carbon stored in arctic permafrost soils, and its oxidation to carbon dioxide (CO2; a greenhouse gas), is predicted to be a major, positive feedback on global warming. However, current estimates of the magnitude of this feedback do not include the oxidation of permafrost soil organic carbon flushed to sunlit lakes and rivers.
Intellectual Merit. This proposed research will be carried out in the Arctic where thawing permafrost and the release of CO2 is predicted to amplify global warming. The goal of the research is to identify the chemical and biological mechanisms by which sunlight and microbes interact to degrade terrestrially-derived dissolved organic carbon (DOC). DOC degradation has been attributed mainly to bacterial activity in sediments and surface waters, but recent findings show that photochemistry plays a substantial, quantitative role in arctic aquatic C cycling. DOC leached from permafrost soils can be very labile to photochemical alteration, which in turn can profoundly alter rates of DOC respiration, microbial community diversity, and the metabolic pathways expressed by microbial communities. Thus, rates of DOC degradation are controlled by both photochemical and microbial processes, but the interaction between these two processes is poorly understood. For example, conceptual models fail to explain (1) what controls the lability of terrestrially-derived DOC to photodegradation, (2) why photo-alteration of DOC can both amplify or reduce microbial processing of DOC, or (3) why rates of DOC respiration vary with microbial community composition. These knowledge gaps will be addressed by examining the intersection between environmental drivers and microbial ecology, specifically by integrating studies of photochemical and biological processing of DOC. This will be accomplished with a set of environmentally-relevant experiments and high-resolution chemical and genetic measurements aimed at (1) identifying molecular pathways and processes controlling lability of DOC to photodegradation, (2) linking the diversity and genetic mechanisms of DOC-respiring microbial communities to the chemistry of the biologically relevant portions of terrestrial DOC, and (3) quantifying the metabolic response of diverse microbial communities to the photochemical production or removal of DOC compounds.
This research was supported by NSF CAREER 1351745, DEB 1637459, 1754835 and 1754835