Discovering The Molecular Basis For Carbon Storage In Soil For Food Security And Climate Change Mitigation

恢复和加强土壤中的碳储存在全球范围内被认为是保护我们的环境、减缓气候变化和通过提高农业可持续性来巩固粮食安全的关键优先事项。一个多世纪以来，人们普遍认为，有机化合物在土壤中的持久性是其化学结构固有的“可分解性”的函数，也就是说，与“稳定”的、不易降解的化合物相比，不稳定且容易水解/氧化的化合物更容易矿化。目前的观点更多地强调土壤基质赋予的物理化学保护，作为化合物持久性的主要调节因素。然而，土壤有机碳(SOC)包含了从低分子化合物到大分子结构，从非极性分子到高极性分子的各种碳形式，每种形式在任何土壤中都表现出不同的保护程度。小的极性分子(主要是微生物衍生的)可以通过与土壤矿物质的结合来保护，而大分子和非极性脂类(主要是植物衍生的)则通过土壤团聚体中的封闭而受到保护。如果这些是控制不同有机化合物在土壤中长期存留的主要机制，那么这就增加了稳定能力可能饱和的可能性，如果要大幅提高农业土壤的碳储存，可能需要对其本身进行管理。现在可以通过使用新的化合物/化合物类特定放射性碳测量来确定特定化合物的装载能力、饱和程度和储存率。位于布里斯托尔的BRAMS设施是从土壤中提取和纯化不同化合物以进行放射性碳测年的领先国际中心。我们将应用这些最先进的技术，以及已建立的土壤分级方法，从Rothamsted Research的长期实验(LTES)中收集样本。通过对LTE的当代土壤和存档土壤进行采样，我们可以利用历史上的14C“炸弹峰值”，即20世纪50年代和60年代进行的核弹试验，将最近的碳追踪到矿物保护池和集合体池中的不同化合物类别。不同的有机和矿质肥料应用、农业管理(例如，可耕种的牧草和永久的牧草)以及不同的土壤类型(例如，更多的“粘质”和更多的“沙质”)为确定土壤碳储量的长期控制提供了独特的机会。因此，首次有可能确定不同稳定机制在控制不同化合物类别的长期储存方面的相对作用，以及不同农业管理下土壤中碳储量增加、减少或保持不变的确切原因。土壤科学的进展被用来为提高土壤碳储量的实际管理策略提供参考是至关重要的。因此，为了最大限度地发挥我们项目的影响，所产生的机械理解将用于开发、测试和验证最常用的土壤有机碳模型之一的新版本(RothC，该模型在全球拥有约3,500名用户)。RothC在参数化方面是保守的，这使得它对最终用户非常有吸引力，并且，根据我们的哪些假设得到支持，我们已经确定了可以进行的结构性改变，以改进模型，同时保持其低输入要求。更新后的模型将使用从其他LTE生成的独立数据集以及对一系列环境和土地管理情景中SOC变化的观测数据进行严格测试。一旦得到验证，新的RothC模型将是一个重要的工具，可以告诉人们土地管理将如何影响不同土壤类型和地理位置的SOC动态。

Recovering and enhancing carbon storage in soils is recognised globally as a key priority for protecting our environment, mitigating climate change and underpinning food security by improving agricultural sustainability. For over a century it has been the accepted wisdom that the persistence of organic compounds in soil was a function of the inherent 'decomposability' of their chemical structure, i.e. labile and readily hydrolysable/oxidised compounds are more readily mineralised compared to 'stable' less-easily degraded compounds. Current opinion places far more emphasis on physico-chemical protection, conferred by the soil matrix, as the major regulator of compound persistence. However, soil organic carbon (SOC) comprises a vast diversity of carbon forms ranging from low molecular weight compounds to large macromolecular structures, and from non-polar to highly polar molecules, each exhibiting a differing degree of protection in any soil. Small polar molecules (mainly microbially derived) may be protected by association with soil minerals whilst it has been suggested that macromolecules and non-polar lipids (mainly plant derived) are protected through occlusion within soil aggregates. If these are the dominant mechanisms controlling the long-term persistence of different organic compounds in soils, then this raises the potential that stabilisation capacities could saturate and may themselves need to be managed if carbon storage in agricultural soils is to be substantially enhanced. Determination of compound-specific loading capacities, saturation levels and storage rates is now possible through the use of novel compound/compound class-specific radiocarbon measurements. The BRAMS facility at Bristol is a leading international centre for the extraction and purification of different compounds from soils for radiocarbon dating. We will apply these state-of-the-art techniques, together with established soil fractionation methods, to samples collected from the Long-Term Experiments (LTEs) at Rothamsted Research. By sampling contemporary and archived soils from the LTEs we can exploit the historical 14C-'bomb spike', arising from nuclear bomb testing in the 1950s and 1960s, to trace recent carbon into different compound classes in mineral-protected and aggregate pools. The contrasting organic and mineral fertiliser applications, agricultural managements (e.g. arable vs. permanent grass), and different soil types (e.g. more-'clayey' vs. more-'sandy') provide a unique opportunity for determining how soil carbon storage is controlled in the long term. Thus, for the first time it is possible to identify the relative roles of different stabilisation mechanisms in controlling the long-term storage of different compound classes, and the precise reasons why carbon stocks are increasing, decreasing or remaining constant in soils under different agricultural managements.It is essential that advances in soil science are used to inform practical management strategies for enhancing soil carbon storage. Thus, to maximise the impact of our project, the mechanistic understanding produced will be used to develop, test and validate a new version of one of the most-used soil organic carbon models (RothC, which has ~3,500 users globally). RothC is conservative in terms of parameterisation making it highly attractive to end users, and, depending on which of our hypotheses are supported, we have identified structural changes that could be made to improve the model while maintaining its low input requirements. The updated model will be rigorously tested with independent data sets generated from other LTEs and observations of SOC variation across a range of environmental and land management scenarios. Once verified, the new RothC model will represent an important tool to inform how land management will affect SOC dynamics in different soil types and geographical locations.