ETBC; Temperature sensitivity of substrate decomposition from enzymes to microbial communities

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Soils contain more than 1.5 times the amount of carbon in vegetation and the atmosphere combined, much of it residing in compounds that turnover relatively slowly. Chemical theory predicts that decomposition of slow turnover compounds will be far more sensitive to a warming climate than compounds with faster turnover rates. The release of CO2 to the atmosphere from these compounds as they decompose would serve as a positive feedback to global warming. However, recent research suggests that microorganisms responsible for decomposing soil carbon may adapt or acclimate to warmer environments. Such adaptation or acclimation may mitigate the temperature sensitivity of soil organic carbon decomposition currently predicted by chemical theory. To date, acclimation and adaptation have yet to be incorporated into a predictive framework for the temperature sensitivity of soil organic carbon decomposition, because the influence of microbial acclimation and adaptation to a new temperature regime is, as yet, unknown. For this project then, investigators will determine: i) the influence of microbial acclimation and adaptation on carbon and nitrogen fluxes through microbes and on temperature sensitivities of decomposition for multiple types of carbon compounds; and ii) the influence of interactions between functionally different microbial populations on the temperature sensitivity of soil organic carbon decomposition. Data characterizing responses of microbial decomposition to warming will be incorporated into a theoretical framework to understand the influence of microbial acclimation and adaptation on the temperature sensitivity of soil organic carbon decomposition. Incubations will be performed across a range of complexity, including: simple, sterile mixtures of enzymes and substrates; soil-like media containing substrates of specified structure and isotopic composition, and inoculated with microbial populations representing a range of biogeochemical functions; and real soils with both introduced and natural microbial communities. The flow of carbon and nitrogen into microbes from soil compounds and subsequent release of CO2, shifts in substrate use, and changes in microbial community structure with temperature will be assessed. Models used to predict how soil organic carbon decomposition rates change with temperature are important because they can help predict future atmospheric CO2 concentrations. Currently, most models are based purely on the characteristics of soil organic carbon. Efforts to examine the acclimation and adaptation of the microorganisms that transform soil carbon into biomass and CO2 with changing temperature typically are thwarted due to the challenges associated with identifying microbial use of distinct soil carbon compounds. By conducting experiments across incremental levels of experimental complexity and integrating measurements of carbon and nitrogen flow through microorganisms into a new theoretical framework, this research will directly address these shortcomings. The work will support one post-doctoral scholar, one graduate student, and four undergraduates. Research results will be integrated into seven undergraduate and graduate courses, and educational outreach efforts will include dissemination of soil ecology and climate warming information via laboratory websites, and to middle school students and teachers from rural Kansan populations.