SitS: Collaborative Research: Soils are signaling shifts in aggregate life-cycles: What does this mean for water, carbon and climate feedbacks in the Anthropocene?

健康的土壤支持粮食生产，储存降雨，输送和过滤地下水，并为植物、动物和微生物提供栖息地。这些土壤的大部分体积是由代表颗粒（如粘土）和有机物质（由植物和微生物产生）结合成更大单位的团聚体组成的。这些较大的聚集体单位如何排列控制着聚集体之间孔隙的形状，从而控制着孔隙网络的特征。因此，团聚体的排列决定了水如何在土壤中流动。有趣的是，聚合体有一个生命周期：它们形成，持续一段未知的时间，然后降解。最近的几项研究表明，聚集物在这一生命周期中的移动速度是由降雨、温度和土地利用模式的变化控制的。本研究旨在明确各种尺度上环境驱动因素和集合体生命周期之间的联系：从非常小的个体集合体，到它们在土壤剖面上对水流的排列和影响，最后，它们如何影响山坡、区域和大陆尺度上的水流。在这些更大的尺度上，本研究将揭示这些总体生命周期和安排对影响土壤湿度、植被和气候的作用。这项工作的结果将揭示土壤如何对气候变化作出反应，以及这些反应如何反过来影响气候，促进模型开发以预测气候变化对水资源、粮食生产和生态系统的影响，并促进制定适应未来环境现实的战略。本研究的目的是将土壤团聚体生命周期和排列与水流、碳循环和从土壤颗粒到大陆尺度的生物地球化学通量机械地联系起来。土壤团聚体有机碳（SOC）是决定土壤孔隙和水力学性质的关键结构组分。因此，通过研究控制土壤团聚体形成和崩塌速率的生物和非生物机制，研究人员可以量化和预测土壤结构对气候和土地利用变化的结构响应，而这些特征在当前的建模框架中很大程度上被忽视了。为了实现这一目标，我们的多学科团队将利用来自现有环境观测站（例如，美国农业部，美国国家科学基金会资助的长期研究站点）和国家生态观测站网络站点的土壤样本和数据，以及辅助数据（例如，自然资源保护局土壤气候分析网络和遥感产品），这些数据代表了气候、土地利用和土壤质地的梯度：1)研究土壤团聚体形成和崩塌、排列和孔隙几何的生物和非生物驱动因素，通过可操作实验量化黏结剂丰度、矿物表面积和随土壤深度变化的覆盖层压力对这些轨迹的影响；2)将团聚体形成和崩塌的总速率与微生物活动和有机碳矿化速率联系起来；3)量化聚集体排列如何以及在多大程度上影响孔隙度，从而影响水和碳随深度的通量；4)开发利用遥感土壤水分和土壤表面植被特性预测土壤团聚体深度分布及相关特性的新工具；5)将经验量化的土壤过程从个体团聚体到土墩尺度的机理理解整合到斜坡到流域尺度模型中，以预测土壤生物地球化学对土壤孔隙发育变化的响应；6)模拟大陆尺度上群落生命周期和排列变化对土壤系统生物地球化学的影响及其对气候的反馈。这项研究的进展将提高对土壤在现在和未来发挥生态系统服务能力的认识，阐明影响生态系统中水和碳的通量、转化和储存的物理、化学和生物地球化学过程。该奖项是通过土壤信号（sit）征集活动获得的，该征集活动是美国国家科学基金会和美国农业部国家粮食和农业研究所（USDA NIFA）之间的合作伙伴关系。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。

Healthy soils support the production of food, store rainfall, transmit and filter groundwater, and provide habitat for plants, animals, and microbes. Much of the volume of these soils is comprised of aggregates that represent the binding of particles (e.g., clay) and organic matter (generated by plants and microbes) into larger units. How these larger aggregate units are arranged controls the shapes of pores between aggregates, and thus the characteristics of the pore network. As a result, aggregate arrangement governs how water flows through soil. Interestingly, aggregates have a life-cycle: they form, persist for largely unknown time periods, and then degrade. Several recent studies suggest that the speed at which aggregates move through this life-cycle is controlled by changes in rainfall, temperature, and land-use patterns. This research aims to make explicit linkages between environmental drivers and aggregate life-cycles across various scales: from very small individual aggregates, to their arrangements and effects on water flow through a soil profile, and, finally, how they influence water flow at hillslope, regional, and continental scales. At these broader scales, this study will uncover the role that these aggregate life-cycles and arrangements have on influencing soil moisture, vegetation and climate. Findings from this work will reveal how soils respond to changing climate and how those responses can in turn influence climate, facilitate model development for forecasting the impacts of climate change on water resources, food production and ecosystems, and promote the development of strategies to adapt to future environmental realities. The goal of this research is to mechanistically link soil aggregate life-cycles and arrangements to water flow, carbon cycling, and biogeochemical fluxes from soil particles to continental scales. Aggregate soil organic carbon (SOC) is a key structural component that gives rise to the soil pore and hydraulic properties observed at broader soil horizon and pedon scales. Thus, by examining both biotic and abiotic mechanisms governing rates of formation and collapse of soil aggregates, investigators can quantify and project the structural response of the soil fabric to changing climate and land use—features largely overlooked in current modeling frameworks. To accomplish this goal, our multi-disciplinary team will leverage soil samples and data from existing environmental observatories (e.g., United States Department of Agriculture, NSF-funded long-term research sites) and National Ecological Observatory Network sites, as well as ancillary data (e.g., Natural Resources Conservation Service Soil Climate Analysis Network and remotely sensed products), that represent gradients of climate, land use, and soil texture to: 1) investigate biotic and abiotic drivers of soil aggregate formation and collapse, arrangement, and pore geometry through manipulative experiments that quantify the influence of binding agent abundance, mineral surface area, and overburden pressure, which varies with soil depth, on these trajectories; 2) relate gross rates of aggregate formation and collapse to rates of microbial activity and SOC mineralization; 3) quantify how and to what degree aggregate arrangements influence porosity and, thus, water and C fluxes with depth; 4) develop new tools that leverage remotely-sensed soil moisture and vegetation properties at the soil surface to predict depth distributions of soil aggregate and related properties; 5) integrate a mechanistic understanding of empirically quantified soil processes from the individual aggregate to the pedon scale into hillslope- to watershed-scale models to project soil biogeochemical responses to changes in soil pore development; and, 6) model the continental-scale effects of changing aggregate life-cycles and arrangements on the biogeochemistry of soil systems and resulting feedbacks to climate. Advances from this research will improve understanding of soil capacity to perform ecosystem services now and in the future, elucidating physical, chemical, and biogeochemical processes affecting fluxes, transformation, and storage of water and C in ecosystems.This award was made through the Signals in the Soil (SitS)" solicitation, a collaborative partnership between the National Science Foundation and the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA).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.