Unfrozen water availability controls microbial temperature dependence of CO2 production in frozen soils

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High latitude cold regions are warming more than twice as fast as the rest of the planet, with the greatest warming occurring during the winter. Given that a major process responsible for carbon dioxide (CO2) emissions and microbial respiration, increases with warming even at sub-zero temperatures, the CO2 emissions during the non-growing season (NGS; fall, winter, spring) are expected to increase as the climate warms. In addition to the temperature-dependence of microbial metabolic activity, soil organic matter decomposition during the NGS can also be inhibited by soil freezing, which limits the supply of molecular oxygen (O2) and the availability of unfrozen liquid water. Therefore, a comprehensive understanding of partitioning between a temperature response and the effect of unfrozen water availability on soil CO2 production at low temperatures is essential not only for predicting the fate of the vulnerable carbon stocks in northern terrestrial ecosystems, but for accurate predictions of carbon balances and creating climate adaptation and mitigation strategies. The proposed Discovery Grant program seeks to fill a fundamental gap in our understanding of temperature dependence of CO2 production in frozen soils and the transient response of soil biogeochemistry to winter climate warming. The proposed approach combines the detailed measurements of gas-phase and aqueous phase chemistry, to quantify the rates of soil microbial respiration during freeze-thaw cycles, as well as the changes in microbial community structure and the interactive effects of temperature and unfrozen water content on microbially-mediated soil CO2 efflux. The laboratory experiments are designed to assess soil hydrophysical parameters and biogeochemical rates and fluxes that regulate major microbial metabolic processes. The experimental results will improve the fundamental process-based understanding of winter soil biogeochemical processes and will be integrated in the reactive transport and bioenergetics modelling to simulate the biogeochemical transformations of carbon and nutrients and microbial reaction networks under variable winter warming scenarios. This will be a significant step forward in long-term objective of my Discovery Grant program to create the foundation for predictively simulate reaction dynamics in cold regions' subsurface environments, by identifying the dominant biogeochemical drivers of winter soil geomicrobial activity under current and future climate change scenarios. The outcomes of this Discovery Grant research will be a valuable knowledge translation tool in facilitating the percolation of scientific data and knowledge on the climate-sensitivity of carbon dynamics in northern ecosystems and in developing robust climate change adaptation strategies. The proposed research will provide students with innovative and enhanced training and a competitive edge to pursue careers in earth and environmental sciences in academic, government or private sectors.