Contrasting roles of fungal necromass and mineral preservation in influencing mineral-associated organic carbon across and within elevation bands.

Mineral-associated organic carbon (MAOC) is a persistent fraction of soil organic carbon (SOC) that is central to long-term carbon (C) persistence and climate mitigation. Along an elevation gradient, soil texture and chemistry vary with climate and coincide with shifts in microbial communities, but it remains unclear whether MAOC aligns more strongly with abiotic soil attributes or biotic microbial necromass, and whether these relationships change from across-gradient patterns to within-elevation variation. In this study, we investigated SOC fractions in a subtropical mountain system and examined the factors associated with MAOC variation across the elevation gradient and within elevation bands. Across the elevation gradient, MAOC variation was best explained by elevation-associated changes in soil mineral properties, including amorphous Fe oxide, clay + silt content and pH. In contrast, within individual elevation bands, MAOC was positively correlated with total microbial necromass carbon (TNC). In addition, fungal necromass carbon (FNC) explained more variation in MAOC than bacterial necromass carbon (BNC); and TNC was significantly correlated with fungal community composition within bands. Notably, the relationship between TNC and MAOC weakened with increasing elevation. Taken together, our results indicate that MAOC patterns along the elevation gradient are primarily linked to mineral preservation, whereas within-band variation in MAOC is more closely related to bulk-soil microbial necromass C. These findings may help to reconcile conflicting views on MAOC regulation and highlight the context-dependency of soil C stabilization.