Dissolved organic carbon-mediated multi-trophic networks define microbial necromass accumulation in Mollisols of Northeast China

Dissolved organic carbon (DOC) fuels soil micro-food webs, yet how its chemical heterogeneity mediates the multi-trophic regulation of microbial necromass carbon (MNC) remains a major scientific challenge. Specifically, it is unclear how DOC quality links bottom-up resource supply with top-down predatory control to regulate MNC accumulation. Here, we leveraged a natural temperature gradient across Mollisol regions of Northeast China to generate a diverse range of DOC profiles and microbial communities. We found that increasing mean annual temperature (MAT) significantly reduced DOC, soil organic carbon (SOC), and both bacterial and fungal necromass carbon (BNC and FNC). The BNC and FNC contents increased with DOC, particularly with humic- and protein-like fractions. The qPCR analysis revealed that the abundances of lower-trophic groups (bacteria and fungi) were positively correlated with these DOC components, while higher-trophic groups (protists and nematodes) showed a negative correlation. These shifts simplified and destabilized micro-food webs by increasing intra-trophic associations and decreasing cross-trophic associations, ultimately contributing to BNC and FNC accumulation. Collectively, this study proposes a conceptual framework where higher DOC content, particularly humic- and protein-like fractions, stimulates lower-trophic growth, reduces cross-trophic interactions, and enhances MNC formation. By integrating resource heterogeneity with multi-trophic associations, this study provides a mechanistic explanation for how soil food webs regulate carbon stabilization, suggesting that strategic management of DOC quality and trophic network structure can enhance soil carbon sequestration under sustainable management.