OPP-PRF: Freeze-thaw effect on Biogeochemistry and Nutrient Cycling in Arctic Soils

变暖的气温正在迅速融化北极的冻土（永久冻土）。当冻土融化时，它会经历高于冰点和低于冰点的温度波动，这被称为冻融循环。冻融可以影响氮和磷等重要营养物质的可用性，微生物的活动，土壤水分和相关的氧合变化，以及土壤融化释放的温室气体。永久冻土融化的冻融影响在北极被放大，北极储存了全球近一半的土壤碳。这项研究将确定以前的冻土暴露于冻融如何改变土壤功能和养分有效性。该项目支持一名博士后学者，并将资助冻融研究和为北极数据集开发教育R/RStudio模块。冻融是一个破坏性的、温度驱动的过程，对非生物和生物土壤性质及其耦合相互作用有直接影响。不断上升的气温使以前无法获得的化合物暴露于植物吸收、微生物活动、矿物质吸收和沉淀中，同时也改变了解冻土壤中的生物地球化学过程。冻融已被记录为影响土壤溶质（如磷、氮和铁）在非永久冻土中通过冷冻吸力的迁移。在受冻土影响的土壤中，冻融引发的溶质迁移可能与微生物细胞裂解和死亡或土壤团聚体不稳定和断裂后向土壤环境的营养脉冲相吻合。在高寒和草地系统中，冻融过程中的低温吸吮会增加土壤的缺氧条件，导致不同程度的铁还原，并对土壤芳烃和溶解有机碳浓度产生后续影响。冻融循环次数、冻结速率和冻融的空间分布可能会发生变化，从而改变冻融过程中的运输程度，并为微生物的适应和恢复提供信息。该工作将结合野外数据和冻融实验，研究冻融的时空变化及其对阿拉斯加冻土带永久冻土带坡地梯度土壤生物地球化学关键过程的直接影响。研究人员将验证一个假设，即永久冻土土壤化学在第一次冻融循环中会发生变化，从而导致在随后的冻融过程中氧化还原和养分有效性的持续变化。该研究旨在重构我们对永久冻土融化的理解，包括土壤养分状况、氧化还原化学和微生物群落对冻结速率、重复冻融和冻融循环空间变化的响应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Warming air temperatures are thawing frozen ground (permafrost) in the Arctic at a rapid rate. As frozen ground thaws it undergoes temperature fluctuations above and below freezing, known as freeze-thaw cycles. Freeze-thaw can impact the availability of important nutrients such as nitrogen and phosphorus, the activity of microorganisms, soil moisture and associated changes in oxygenation, and the release of greenhouse gases from thawing ground. The implications of freeze-thaw in thawing permafrost are amplified in the Arctic, which stores just under half of all soil carbon across the globe. This research will determine how exposure of previously frozen ground to freeze-thaw alters soil function and nutrient availability. This project supports one postdoctoral scholar and will fund freeze-thaw research and the development of an educational R/RStudio module for an Arctic dataset.Freeze-thaw is a disruptive, temperature driven process with direct impacts to both abiotic and biotic soil properties and their coupled interactions. Rising air temperatures expose previously unavailable compounds to plant uptake, microbial activity, and mineral sorption and precipitation while also altering biogeochemical processes within thawed soil. Freeze-thaw has been recorded to influence the migration of soil solutes (such as P, N, and Fe) through cryosuction in non-permafrost soils. In permafrost-affected soils, freeze-thaw triggered solute migration may coincide with nutrient pulses to the soil environment following microbial cell lysis and death or soil aggregate instability and breakage. In alpine and grassland systems, cryosuction during freeze-thaw can increase anoxic soil conditions with varying levels of Fe reduction and result in subsequent impacts to soil aromatics and dissolved organic carbon concentrations. The number of freeze-thaw cycles, freezing rate, and spatial distribution of freeze-thaw may vary, altering the degree of transport during cryosuction as well as informing microbial adaptation and resiliency. The proposed work will combine field data with freeze-thaw experiments to investigate temporal and spatial variations in freeze-thaw and the direct impacts to critical processes of soil biogeochemistry across a hillslope gradient in Alaskan tundra permafrost at the Toolik Field Station. The investigator will test the hypothesis that permafrost soil chemistry will be altered during the first freeze-thaw cycle, resulting in continuous changes in redox and nutrient availability throughout subsequent freeze-thaw. The study aims to restructure our understanding of permafrost thaw to include responses of the soil nutrient regime, redox chemistry, and microbial communities to freezing rate, repeated freeze-thaw, and spatial variation of freeze-thaw cycling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.