LOCKED UP: The role of biotic and abiotic interactions in the stabilisation and persistence of soil organic carbon

人类土地利用导致的土壤有机碳（SOC）流失是21世纪最紧迫的环境挑战之一。有机碳损失导致气候变化，使土壤不适合种植作物，通过作为植物养分的氮(N)和磷(P)的相关损失降低土壤肥力，并降低含水层的持水能力和排水能力——对抗旱和抗洪能力、水质和水的可用性产生不利影响。国际倡议“每英里4”解决了有机碳损失对粮食安全、气候调节和水资源的威胁，旨在通过持续的、渐进的（例如每年0.4%）增加来扭转全球有机碳损失。我们的研究项目旨在转化土壤有机碳生产和持久性过程和机制的基础知识，为土地管理创新提供信息，并量化提高土壤有机碳持久性的能力和时间尺度。“锁定”- SOC股票。我们的假设是，持续的有机碳是由土壤微生物和土壤矿物质之间一系列复杂但可测试的相互作用产生的：1)植物生物量输入到土壤的相对快速的微生物转化，产生；2)特定类别的有机碳化合物，包括细胞外产物和死细胞成分，它们是持久形式的重要前体，然后3)通过化学吸附土壤矿物质来稳定微生物降解，这可以从微生物可达的C库中去除有机碳；4)通过土壤颗粒和土壤有机质的聚集，在物理上防止微生物降解，其中有机碳在颗粒间和颗粒内的孔隙空间中受到微生物降解的保护。我们的方法是进行相关的实验室研究，实地采样和建模，以获得土壤微生物关键功能群的基本知识，微生物操作及其将有机碳转化为形式的速率，然后与矿物质和矿物团聚体一起存在；并量化这些转化和持续形式如何响应不断变化的环境因素——植物输入的C:N比、水分胁迫、本地微生物群落组成、氧化还原状态、离子组成和孔隙水的营养状况、温度和物理干扰。形成持久有机碳的复杂和相互作用阶段将分阶段量化，在微生物培养模型系统中，在构建和真实的土壤基质中，水介质和选定的矿物质，作为土壤环境的理想和实验可处理的表示。在考虑各种环境条件的多因子实验中，我们将根据质量平衡、生物生长、化学质量作用和物理-化学胶体相互作用的第一原理，量化有机碳转化的速率定律和常数。研究结果将应用于现有的土壤过程模型。这一机械知识的进步将使我们能够从对土壤有机碳转化动力学以及由此导致的土壤结构和体积特性变化的强烈第一性原理理解中建立模型模拟。我们将对这些进步进行测试，对照来自农业现场全土芯操作实验的独立数据。从选定的土壤类型和生物群落中获得的额外土壤核，以反映世界各地的特定区域和土地利用，将通过应用机械土壤过程模型进行操作。实验和模型结果将用于评估——对于关键的土壤类型、气候区域和土地利用——可以从假设的土地利用实践中获得的潜在最大值、时间尺度和持久性有机碳，以增加持久性有机碳的储量——例如，通过改变耕作方式、植被覆盖和水管理。

Loss of soil organic carbon (SOC) through human land use is one of the most pressing environmental challenges of the 21st century. SOC loss contributes to climate change, makes soils less suitable for crops, reduces soil fertility through associated loss of nitrogen (N) and phosphorous (P) as plant nutrients, and reduces water holding capacity and drainage to aquifers - adversely impacting drought and flood resistance, water quality and water availability. The international initiative "4 per mille" addresses the threat of SOC loss to food security, climate regulation and water resources and aims to reverse global SOC losses through sustained, incremental (e.g. 0.4 % per year) increases. Our research project aims to transform fundamental knowledge of the processes and mechanisms of SOC production and persistence in soil to inform land management innovation, and quantify the capacity and time scale to increase persistent - i.e. "LOCKED UP" - SOC stocks. Our hypothesis is that persistent SOC is produced by a series of complex but testable interactions between soil microbes and soil minerals: 1) relatively rapid microbial transformation of plant biomass input to soil, which produces; 2) specific classes of SOC compounds including extracellular products and components of dead cells that are essential precursors to persistent forms, which are then 3) stabilised against microbial degradation through chemical sorption to soil minerals, which can remove SOC from the microbially accessible C pool; and 4) physically protected against microbial degradation through aggregation of soil particles and soil organic matter, where SOC is protected from microbial degradation in inter and intraparticle pore spaces. Our approach is to undertake linked laboratory studies, field sampling and modelling to obtain fundamental knowledge of key functional groups of soil microbes, the microbial operations and their rates which transform SOC to forms which then persist with minerals and within mineral aggregates; and to quantify how these transformations and persistent forms respond to changing environmental factors - plant input C:N ratios, water stress, indigenous microbial community composition, redox status, ionic composition and nutrient status of pore waters, temperature, and physical disturbance. The complex and interactive stages of forming persistent SOC will be quantified in stages, in model systems of microbial cultures, aqueous media and selected minerals in built and real soil matrices, as an idealised and experimentally tractable representation of the soil environment. In multi-factorial experiments that account for the range of environmental conditions, we will quantify rate laws and constants for SOC transformations based on first principles of mass balance, biological growth, chemical mass action and physical-chemical colloid interactions. The results will be implemented into an existing soil process model. This advance in mechanistic knowledge will allow us to build model simulations from a strong first principles understanding of the SOC transformation dynamics and resulting changes in soil structure and bulk properties. We will test these advances against independent data from manipulation experiments on whole soil cores from agricultural sites. Manipulation of additional soil cores - obtained from selected soil types and biomes to reflect specific regions and land uses around the world - will be carried out with application of the mechanistic soil process model. The experimental and model results will be used to assess - for key soil types, climate regions and land uses - the potential maximum, time scale and persistence of SOC that can be obtained from hypothesised land-use practices to increase stocks of persistent SOC - e.g. by changing tillage practices, vegetation cover and water management.