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

高纬度寒冷地区的变暖速度是地球其他地区的两倍多，其中冬季变暖最快。考虑到导致二氧化碳排放和微生物呼吸的一个主要过程即使在零度以下也会随着变暖而增加，因此预计非生长期（秋、冬、春）的二氧化碳排放量将随着气候变暖而增加。除了微生物代谢活动的温度依赖性外，NGS过程中土壤有机质分解也会受到土壤冻结的抑制，这限制了分子氧（O2）的供应和未冻结液态水的可用性。因此，全面了解温度响应与低温下可获得的未冻水对土壤二氧化碳产生的影响之间的关系，不仅对于预测北方陆地生态系统中脆弱碳储量的命运至关重要，而且对于准确预测碳平衡以及制定气候适应和减缓战略也至关重要。提出的发现资助计划旨在填补我们对冻土中二氧化碳产生的温度依赖性和土壤生物地球化学对冬季气候变暖的瞬态响应的理解的基本空白。该方法结合气相和水相化学的详细测量，量化冻融循环过程中土壤微生物呼吸的速率，以及微生物群落结构的变化以及温度和未冻水含量对微生物介导的土壤CO2外排的相互作用。实验室实验旨在评估调节主要微生物代谢过程的土壤水物理参数和生物地球化学速率和通量。实验结果将提高对冬季土壤生物地球化学过程的基本认识，并将整合到反应输运和生物能量学模型中，以模拟不同冬季变暖情景下碳和养分的生物地球化学转化以及微生物反应网络。通过确定当前和未来气候变化情景下冬季土壤地质微生物活动的主要生物地球化学驱动因素，这将是我的发现资助计划的长期目标向前迈出的重要一步，为预测模拟寒冷地区地下环境的反应动力学奠定基础。这项发现基金的研究成果将成为一种宝贵的知识转化工具，有助于促进有关北方生态系统碳动态气候敏感性的科学数据和知识的传播，并有助于制定强有力的气候变化适应战略。拟议的研究将为学生提供创新和加强培训，并为他们在学术、政府或私营机构从事地球和环境科学方面的职业提供竞争优势。

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.