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

人类土地利用造成的土壤有机碳损失是21世纪最紧迫的环境挑战之一。SOC损失导致气候变化，使土壤不太适合种植作物，通过相关的氮(N)和磷(P)作为植物养分的损失降低土壤肥力，并降低持水能力和向含水层的排水--对抗旱抗洪、水质和水资源供应产生不利影响。国际倡议“百万分之四”解决了SOC损失对粮食安全、气候监管和水资源的威胁，旨在通过持续、渐进(例如每年0.4%)的增加来扭转全球SOC损失。我们的研究项目旨在转变土壤中有机碳产生和持久性的过程和机制的基本知识，以指导土地管理创新，并量化增加持久性的能力和时间尺度--即。“锁定”--国企股票。我们的假设是，持久性有机碳是由土壤微生物和土壤矿物之间一系列复杂但可测试的相互作用产生的：1)输入到土壤中的植物生物量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亡细胞的成分，它们是持久性形式的基本前体，然后通过对土壤矿物的化学吸附来稳定微生物降解，这可以从微生物可获得的碳库中去除有机碳；以及4)通过土壤颗粒和土壤有机质的聚集，物理上防止微生物降解，其中有机碳受到保护，使其免受微生物在颗粒间和颗粒内孔隙中的降解。我们的方法是进行相关的实验室研究、实地采样和建模，以获得土壤微生物的关键功能群、微生物的操作及其速率的基本知识，这些微生物将有机碳转化为随后与矿物和矿物团聚体一起存在的形式；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态、温度和物理干扰。形成持久性SOC的复杂和相互作用的阶段将在微生物培养、水介质和已建成和真实土壤基质中选定的矿物的模型系统中分阶段量化，作为对土壤环境的理想和实验上易于处理的表示。在考虑环境条件范围的多因素实验中，我们将基于质量平衡第一原理、生物生长原理、化学质量作用原理和物理-化学胶体相互作用原理来量化SOC转化的速率定律和常数。结果将被应用到现有的土壤过程模型中。力学知识的这一进步将使我们能够根据强大的第一原理建立模型模拟，了解土壤有机碳转化动力学以及由此导致的土壤结构和整体性质的变化。我们将根据来自农业场地的整个土壤岩心的操纵实验的独立数据来测试这些进展。将通过应用机械土壤过程模型来操纵额外的土芯--从选定的土壤类型和生物群中获得，以反映世界各地的特定区域和土地用途。实验和模型结果将用于评估关键土壤类型、气候区域和土地利用的SOC的潜在最大值、时间尺度和持久性，这些潜在的最大值、时间尺度和持久性可以通过假想的土地利用做法获得，以增加持久性SOC的存量--例如通过改变耕作做法、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.