Temporal Amplification of Microbial Necromass Contribution to Soil Organic Carbon Under Nutrient Addition

Abstract Nutrient inputs can simultaneously regulate microbial necromass formation and soil organic carbon (SOC) accrual, but whether the contribution of microbial necromass to SOC changes over time under nutrient addition, and whether this temporal dependence differs among residue components remains unclear. We synthesized 303 paired observations of microbial necromass and SOC from 50 global studies to quantify the coupling between SOC responses and the responses of total necromass carbon (TNC), fungal necromass carbon (FNC), and bacterial necromass carbon (BNC), and to test how these relationships changed with experimental duration. Across nutrient input types, combined mineral and organic inputs produced the strongest responses, nitrogen, phosphorus, and potassium fertilization combined with manure increasing TNC, FNC, BNC, and SOC by 42.91%, 40.86%, 51.34%, and 44.01%, respectively. Microbial necromass responses were the strongest predictors of SOC responses, yet necromass increased more rapidly than SOC, indicating that enhanced residue production did not translate proportionally into persistent SOC accrual. The contribution of BNC to SOC was comparatively time independent and was mainly regulated by nutrient type. The contribution of FNC showed a convergent trend over time and was significantly influenced by ecosystem type. In contrast, the experimental duration significantly amplified the contribution of TNC to SOC. These findings indicate that long‐term SOC sequestration is an emergent system property arising from the time‐dependent coordination of distinct stabilization pathways. Accounting for this temporal dependence can refine microbial carbon pump theory and provide a globally relevant basis for improving long‐term soil carbon sink projections and nutrient‐management strategies under global change.