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

高纬度寒冷地区变暖的速度是地球其他地区的两倍多，其中最大的变暖发生在冬季。鉴于二氧化碳(CO2)排放和微生物呼吸的一个主要过程，即使在零度以下的温度下，也会随着变暖而增加，因此非生长季(NGS；秋季、冬季、春季)的二氧化碳排放量预计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，土壤冻结还可以抑制土壤有机质在NGS过程中的分解，从而限制了分子氧(O2)的供应和未冻结液态水的可用性。因此，全面了解低温下温度响应和非冰冻水可获得性对土壤二氧化碳产生的影响之间的分配，不仅对于预测北方陆地生态系统中脆弱的碳储量的命运，而且对于准确预测碳平衡和制定气候适应和缓解战略至关重要。拟议的探索资助计划试图填补我们在理解冻土中二氧化碳产生的温度相关性以及土壤生物地球化学对冬季气候变暖的瞬时响应方面的一个根本空白。该方法结合了详细的气相和水相化学测量，量化了土壤微生物在冻融循环中的呼吸速率，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外流的交互影响。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。实验结果将促进对冬季土壤生物地球化学过程的基本理解，并将被整合到反应运输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和微生物反应网络。这将是我的发现赠款计划长期目标的重要一步，该计划通过识别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，为预测模拟寒冷地区地下环境中的反应动力学奠定基础。这项探索赠款研究的成果将是一个宝贵的知识转化工具，有助于渗透北部生态系统碳动态对气候敏感的科学数据和知识，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增强的培训，以及在学术、政府或私营部门从事地球和环境科学职业的竞争优势。

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.