Data from: A test of the hierarchical model of litter decomposition

Our basic understanding of plant litter decomposition informs the assumptions underlying widely applied soil biogeochemical models, including those embedded in Earth system models. Confidence in projected carbon cycle-climate feedbacks therefore depends on accurate knowledge about the controls regulating the rate at which plant biomass is decomposed into products such as CO2. Here, we test underlying assumptions of the dominant conceptual model of litter decomposition. The model posits that a primary control on the rate of decomposition at regional to global scales is climate (temperature and moisture), with the controlling effects of decomposers negligible at such broad spatial scales. Using a regional-scale litter decomposition experiment at six sites spanning from northern Sweden to southern France – and capturing both within and among site variation in putative controls – we find that contrary to predictions from the hierarchical model, decomposer (microbial) biomass strongly regulates decomposition at regional scales. Further, the size of the microbial biomass dictates the absolute change in decomposition rates with changing climate variables. Our findings suggest the need for revision of the hierarchical model, with decomposers acting as both local- and broad-scale controls on litter decomposition rates, necessitating their explicit consideration in global biogeochemical models.

我们对植物残体分解的基础认知，为各类广泛应用的土壤生物地球化学模型（soil biogeochemical models）——包括内嵌于地球系统模型（Earth system models）的相关模型——的核心假设提供了理论依据。因此，学界对碳循环-气候反馈预测结果的置信度，取决于能否精准掌握调控植物生物质分解为二氧化碳（CO₂）等产物的速率的各类控制因子。本研究针对主流的残体分解概念模型的核心假设展开检验。该模型指出，在区域至全球尺度下，残体分解速率的核心控制因子为气候（温度与湿度），而分解者的调控作用在这类大空间尺度上可被忽略。本研究依托从瑞典北部延伸至法国南部的6个站点开展的区域尺度残体分解实验——该实验覆盖了样点内部及样点间假定控制因子的变异——发现与该层级模型（hierarchical model）的预测结果相悖：在区域尺度上，分解者（微生物）生物量对分解过程具有极强的调控作用。此外，微生物生物量的规模决定了气候变量变化时，分解速率的绝对变化幅度。本研究结果表明，亟需对该层级模型进行修订：分解者同时作为局地与大尺度下残体分解速率的调控因子，因此全球生物地球化学模型中必须明确纳入分解者的相关考量。