Microscale controls on soil organic matter stabilization and impacts on nitrogen cycling in Canadian prairie agroecosystems

加拿大草原农业生态系统土壤有机质稳定性的微观控制及其对氮循环的影响

• 批准号: RGPIN-2017-05905
• 负责人: Walley, Fran
• 金额: $ 3.93万
• 依托单位: University of Saskatchewan
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=765635
• 关键词: Microscale; controls; soil; organic; matter

Nitrogen (N) is a key ecosystem nutrient controlling net primary production in both agricultural and unmanaged ecosystems. During microbial decomposition of soil organic matter, bioavailable inorganic N is released to the environment, with implications for agricultural and environmental sustainability. Despite the importance of this nutrient, our understanding of the many factors controlling N-cycling processes, including the protection (and release) of N from soil organic matter remains incomplete. It has long been recognized that calcium (Ca) plays a role in the protection of soil organic N through ionic associations with soil organic matter (i.e., Ca bridging) and encapsulation of organic matter in Ca minerals precipitated from the soil solution. These physical protection mechanisms typically are attributed to abiotic processes, whereby Ca reacts with organic matter as a consequence of changing soil conditions, such as the wetting and drying cycles that influence Ca solubilization in the soil solution. What remains largely unexplored, however, is the contribution of biotic processesspecifically the action of soil microorganismsto the precipitation of Ca minerals such as calcite, and the consequent protection of soil organic N. Although the role of microbes in the precipitation of calcite has been investigated in a range of aquatic and terrestrial environments, the significance and contribution of microbially-induced precipitation of calcite (MICP) to the physical protection of soil organic N has not been addressed. It has been hypothesized that MICP occurs in Ca-rich environments as a mechanism to protect microbial cells from self-calcification. Moreover, MICP is often associated with the enhanced production of extracellular polymeric substances (EPS) by these same microbes, also as a protection mechanism in Ca-saturated environments. The proposed program explores the possibility that MICP together with the associated production of EPS plays a significant role in soil aggregate stabilization and thus soil organic N protection in Ca-rich soil environments typical of the Canadian prairies. Cutting edge techniques, such as synchrotron-based examinations of soil microaggregate structures, together with molecular identification of the microorganisms responsible for aggregation, will be used to shed light on physical processes at the microscale that contribute to N bioavailability at the macroscale. Ultimately, we need to understand microscale processes before we can successfully develop macroscale strategies to manage N in agroecosystems.

氮 (N) 是控制农业和非管理生态系统中净初级生产的关键生态系统养分。在土壤有机质的微生物分解过程中，生物可利用的无机氮被释放到环境中，对农业和环境的可持续性产生影响。尽管这种养分很重要，但我们对控制氮循环过程的许多因素（包括土壤有机质中氮的保护（和释放））的理解仍然不完整。人们很早就认识到，钙（Ca）通过与土壤有机质的离子缔合（即钙桥）以及将有机质封装在从土壤溶液中沉淀的钙矿物中，在保护土壤有机氮方面发挥作用。这些物理保护机制通常归因于非生物过程，即土壤条件变化导致钙与有机物发生反应，例如影响土壤溶液中钙溶解的干湿循环。然而，生物过程的贡献，特别是土壤微生物对方解石等钙矿物沉淀的作用，以及随后对土壤有机氮的保护，仍然很大程度上未被探索。尽管微生物在方解石沉淀中的作用已在在一系列水生和陆地环境中，微生物诱导方解石沉淀（MICP）对土壤有机氮物理保护的重要性和贡献尚未得到解决。据推测，MICP 发生在富含钙的环境中，作为保护微生物细胞免于自钙化的机制。此外，MICP 通常与这些微生物增强胞外聚合物 (EPS) 的产生有关，同时也是 Ca 饱和环境中的一种保护机制。拟议的计划探讨了 MICP 以及相关 EPS 生产在土壤团聚稳定方面发挥重要作用的可能性，从而在加拿大大草原典型的富钙土壤环境中保护土壤有机氮。尖端技术，例如基于同步加速器的土壤微团聚体结构检查，以及负责聚集的微生物的分子鉴定，将用于揭示微观尺度上有助于宏观尺度氮生物利用度的物理过程。最终，我们需要先了解微观过程，然后才能成功制定宏观策略来管理农业生态系统中的氮。