Water Table Decline Shifts Microbial Necromass From Particulate to Mineral‐Associated Pools in Peatlands

Microbial necromass carbon (MNC) is a major and stable component of soil organic carbon, yet its fraction‐specific accumulation and stabilization mechanisms remain unclear, particularly in peatlands experiencing hydrological change. We investigated MNC distribution along three independent transects spanning a natural gradient of five progressively decreasing water tables across three soil depths (0–20, 40–60, and 80–100 cm) in the Zoige alpine peatland, China. Using amino sugar biomarkers, we quantified bacterial (BNC) and fungal necromass carbon (FNC) in particulate organic matter (POM) and mineral‐associated organic matter (MAOM), and related them to biotic and abiotic drivers. FNC dominated MNC across soil depths and fractions, with enrichment in POM fraction, whereas BNC was proportionally higher in MAOM. Water table decline shifted MNC allocation from POM to MAOM, with the proportion of MAOM‐associated MNC in deep soil increasing from 53.1% to 88.6%, indicating enhanced mineral‐associated stabilization under low water table conditions. In POM, MNC accumulation was co‐regulated by living microbial biomass and soil properties, while in MAOM, MNC stabilization was driven mainly by abiotic factors, specifically by total nitrogen and clay plus silt content. These findings reveal a distinct fraction‐biomarker pathway of microbial carbon persistence in peatlands, thereby improving predictions of MNC dynamics and informing targeted carbon conservation strategies during peatland drainage.