Soil organic matter is the dominant carbon pool in terrestrial ecosystems, and its management is of increasing policy relevance. Soil microbes are the main drivers of soil organic carbon sequestration, especially through accumulation of their necromass. However, since the direct characterization of microbial necromass in soil is challenging, its composition and formation remain unresolved. Here we provide evidence that microbial death pathways (the distinct processes of microbial dying) in soil affect necromass composition and its subsequent fate. Importantly, the composition of derived microbial necromass does not equal that of microbial biomass. From biomass to necromass, distinct chemical transformations lead to increases in cell wall/cytoplasm ratios while nutrient contents and easily degradable compounds are depleted. The exact changes depend on environmental conditions and the relevance of different microbial death pathways, for example, predation, starvation or anthropogenic stresses. This has far-reaching consequences for mechanisms underpinning biogeochemical processes: (1) the quantity and persistence of microbial necromass is governed by microbial death pathways, not only the initial biomass composition; (2) efficient recycling of nutrients within microbial biomass presents a possible pathway of organic carbon sequestration that minimizes nitrogen losses; (3) human-induced disturbances affect the causes of microbial death and consequently necromass composition. Thus, new research focusing on microbial death pathways holds great potential to improve management strategies for soil organic carbon storage. Not only microbial growth but also death drive the soil microbial carbon pump.

土壤有机质是陆地生态系统中主要的碳库，其管理与政策相关性越来越高。土壤微生物是土壤有机碳固存的主要驱动力，尤其是通过积累它们的坏死物质。然而，由于直接表征土壤中的微生物坏死物具有挑战性，其组成和形成仍未得到解决。在这里，我们提供的证据表明土壤中的微生物死亡途径（微生物死亡的不同过程）会影响坏死物质的组成及其随后的命运。重要的是，衍生的微生物坏死物的组成不等于微生物生物量的组成。从生物质到坏死物质，不同的化学转化导致细胞壁/细胞质比率增加，同时营养成分和易降解化合物被耗尽。确切的变化取决于环境条件和不同微生物死亡途径的相关性，例如捕食、饥饿或人为压力。这对支撑生物地球化学过程的机制具有深远的影响：(1) 微生物坏死的数量和持久性受微生物死亡途径的控制，而不仅仅是初始生物量组成；(2) 微生物生物质中养分的有效循环提供了一种可能的有机碳封存途径，可最大限度地减少氮损失；(3) 人为干扰会影响微生物死亡的原因，从而影响死尸的组成。因此，以微生物死亡途径为重点的新研究在改进土壤有机碳储存的管理策略方面具有巨大潜力。