Response of soil biogeochemistry to freeze-thaw cycles and implications for the soil respiration-climate feedback: A process-oriented experimental approach

土壤生物地球化学对冻融循环的响应及其对土壤呼吸-气候反馈的影响：面向过程的实验方法

• 批准号: RGPIN-2015-03801
• 负责人: Rezanezhad, Fereidoun
• 金额: $ 1.46万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708449
• 关键词: Response; soil; biogeochemistry; freeze; thaw

Freeze-thaw cycles represent a major climate forcing acting on soils at middle and high latitudes. Freezing and thawing of soils affect their physical properties, biogeochemical processes, microbial community, and carbon and nutrient budgets. Although research during the last few decades has revealed the large effects freeze-thaw cycles have on greenhouse gas emissions and chemical leaching from soils, the underlying hydrological, physical, geochemical and microbial mechanisms, and their mutual interactions, remain poorly understood. One reason is the paucity of time-series data that capture the relevant transport and reaction processes within the soil system during freeze-thaw cycles. As a consequence, we are currently seriously limited in our ability to predict the response of soil processes to changes in the frequency, magnitude and duration of freeze-thaw events driven by ongoing and future climate change. The central aim of this Discovery Grant research is to unravel the coupled physical, hydrological and biogeochemical processes in soils that, together, regulate the production of greenhouse gases and changes in microbial activity and pore water composition during freeze-thaw cycles. The proposed approach combines the acquisition of integrated physical, chemical and microbial data in a newly-developed soil column system in which time-dependent, vertical temperature profiles are generated that mimic temperature distributions in real soils under freeze-thaw conditions. The research will be broken down in four highly innovative interrelated (sub-)projects. Project 1 will document the subsurface changes in oxygen (O2) concentrations in a soil experiencing successive periods of freezing and thawing, using multi-fiber optode microsensors. In Project 2, detailed measurements of in situ gas-phase and aqueous phase chemistry will be carried out, in order to delineate the pathways and quantify the rates of soil microbial respiration during freeze-thaw cycles. Project 3 will focus on the changes in soil physical and hydraulic properties, as well as the changes in microbial community structure, caused by freezing and thawing. Project 4 will integrate and link the experimental results of Projects 1-3 into a reactive transport model framework that will be able to account for soil biogeochemical processes under freeze-thaw conditions. The outcomes of the project enhance the interpretation of field-scale measurements of greenhouse gas emissions from middle and high latitude soils, and enable informed predictions about the changes in these gas emissions, as well as groundwater quality under scenarios of climate change.

冻融循环是作用于中高纬度土壤的主要气候强迫。土壤的冻结和融化会影响其物理特性、生物地球化学过程、微生物群落以及碳和养分预算。尽管过去几十年的研究揭示了冻融循环对温室气体排放和土壤化学浸出的巨大影响，但人们对潜在的水文、物理、地球化学和微生物机制及其相互相互作用仍然知之甚少。原因之一是缺乏捕获冻融循环期间土壤系统内相关传输和反应过程的时间序列数据。因此，我们目前预测土壤过程对由当前和未来气候变化驱动的冻融事件的频率、幅度和持续时间变化的响应的能力受到严重限制。这项发现资助研究的中心目标是揭示土壤中物理、水文和生物地球化学的耦合过程，这些过程共同调节冻融循环期间温室气体的产生以及微生物活动和孔隙水成分的变化。所提出的方法结合了在新开发的土壤柱系统中采集综合物理、化学和微生物数据，在该系统中生成随时间变化的垂直温度剖面，模拟冻融条件下真实土壤的温度分布。该研究将分为四个高度创新的相互关联（子）项目。项目 1 将使用多光纤光极微传感器记录经历连续冻融期的土壤中氧气 (O2) 浓度的地下变化。在项目2中，将对原位气相和水相化学进行详细测量，以描绘冻融循环期间土壤微生物呼吸的路径并量化其速率。项目3将重点研究冻融引起的土壤物理和水力性质的变化，以及微生物群落结构的变化。项目 4 将把项目 1-3 的实验结果整合并链接到反应传输模型框架中，该框架将能够解释冻融条件下的土壤生物地球化学过程。该项目的成果增强了对中高纬度土壤温室气体排放实地测量的解释，并能够对气候变化情景下这些气体排放以及地下水质量的变化进行明智的预测。