Rhizosphere as a hotspot for microbial necromass deposition into the soil carbon pool

Microbial leftovers, known as necromass, are key players in storing carbon in the soil around plant roots (i.e. rhizosphere), a zone characterized by high‐efficiency microbial anabolism. Yet, the extent and mechanisms through which the rhizosphere contributes to soil organic carbon (SOC) via microbial necromass, especially under changing environments remain unclear. We aimed to evaluate the contributions of microbial necromass to SOC and influencing factors from the rhizosphere perspective. We collected the rhizosphere and bulk soil from 39 alpine coniferous forest sites on the eastern Tibetan Plateau to assess the extent of microbial necromass contribution to SOC in the rhizosphere from a dynamic perspective by calculating the ratio of increased amino sugars (AS) to increased SOC in the rhizosphere relative to that in bulk soil (RAS/SOC). We also collected climate data and determined nutrient concentrations and microbial physiological traits in rhizosphere soil to elucidate the factors affecting RAS/SOC. The results showed that across all sampling sites, the average concentrations of SOC‐normalized AS in the rhizosphere were significantly higher than those in the bulk soil. Furthermore, the average RAS/SOC was greater than 1, indicating a faster microbial necromass accumulation than SOC accumulation in the rhizosphere. These results implied that the rhizosphere sustains a greater capacity for microbial necromass contribution to the SOC pool than the bulk soil does. Soil nutrient availability was the primary factor affecting RAS/SOC, and precipitation indirectly affected microbial anabolism and RAS/SOC by changing soil nutrient status. Additionally, with increasing rhizosphere soil nutrient availability, microbial carbon‐use efficiency and growth rate increased but the biomass‐specific enzyme activity declined, indicating that microorganisms tended to exhibit high‐yield strategies with increasing soil nutrient availability. Synthesis. Our findings underpin the vital effect of microbial necromass in SOC accumulation from the rhizosphere perspective and offer valuable insights into mechanisms underlying microbial C metabolic processes in rhizosphere SOC accumulation under changing environments. 摘要 微生物残体是植物根系周围的土壤(即根际)碳储存的关键驱动者，该区域以高效的微生物合成为特征。然而，在不断变化的环境下，根际微生物残体对土壤有机碳(SOC)的贡献程度和机制仍不清楚。我们旨在从根际视角评估微生物残体对SOC的贡献并辨识其影响因素。 我们从青藏高原东部39个高寒针叶林样点采集了根际和非根际土壤，通过计算根际相对于非根际土壤中增加的氨基糖与增加的SOC的比值(RAS/SOC)评估了微生物残体对根际SOC积累的贡献幅度。同时，我们还收集了气候数据，并测定了根际土壤中的养分浓度和微生物生理属性，以阐明影响RAS/SOC