Evaluation of the relative importance to carbon sequestration and nutrient cycling of root exudation, and turnover of roots and mycorrhizas

维持土壤功能和碳储存是可持续农业的关键目标。大多数C、N和P通过活根的渗出和死根及其相关共生体的周转返回土壤。因此，植物固定的碳以二氧化碳的形式返回到大气中的速率和营养物质被循环利用到植物可利用的形式的速率是紧密耦合的。然而，碳和营养的三个最重要的地下通量(根分泌物和根和菌根周转)的定量分离在很大程度上仍然没有实现。这既是因为对C、N和P化合物及其聚合物(如蛋白质、核酸、纤维素、木质素和甲壳素)进入土壤的命运了解有限，也是因为缺乏测量释放速率的适当技术。因此，缺乏对这些通量的了解是理解和模拟大气碳在土壤中的储存以及控制养分循环的因素的主要障碍。我们建议利用最新的技术进步来确定：(1)温带永久草地根部和菌根周转过程中向土壤输送的C、N、P的相对数量和类型。(2)土壤微生物利用这些过程向土壤输送的各种形式的碳的速度和途径，以及这如何控制碳以二氧化碳的形式返回大气。(3)与植物C向CO2矿化的同步程度是N和P向植物有效形态的回归。(4)用最先进的技术测量的根和菌根周转量与用更传统的方法测量的根和菌根周转量的估计如何比较。

Maintaining soil function and carbon storage represent key objectives in sustainable agriculture. Most C, N and P is returned to soil via exudation from live roots, and turnover of dead roots and their associated symbionts. Consequently, both the rate at which C fixed by plants is returned to the atmosphere as CO2 and the rate at which nutrients are recycled to plant-available forms are tightly coupled. However, quantitative separation of the three most important below-ground fluxes of C and nutrients (root exudation and root and mycorrhizal turnover) remains largely unachieved. This is due both to limited understanding of the fate of the range of C, N and P compounds and their polymers (e.g. protein, nucleic acids, cellulose, lignin and chitin) delivered to soil, and to a lack of suitable techniques to measure rates of delivery. Consequently, poor knowledge of these fluxes is a major impediment to understanding and modelling the storage of atmospheric C in soils and the factors controlling nutrient cycling. We propose to utilise recent technological advances to determine: (1) The relative quantities and types of C, N and P delivered to the soil in turnover of roots and mycorrhizas in temperate permanent grassland. (2) The rate and route of utilisation by soil microbes of the various forms of C delivered to the soil by these processes and how this controls the delivery of C back to the atmosphere as CO2. (3) How synchronous with mineralisation of plant C to CO2 is the return of N and P to plant-available forms. (4) How estimates of root and mycorrhizal turnover measured by state-of-the-art techniques compare with those from more traditional approaches.