Plant detritus carbon dominates over microbial necromass carbon in topsoil of alpine ecosystems

Determining microbial necromass carbon and plant detritus carbon is essential for accurate global soil organic carbon modeling. Yet soil organic carbon precursors are usually ignored in alpine assessments. We examined 363 samples from dominant Himalayan ecosystems and determined the distribution of microbial necromass carbon and plant detritus carbon in 0-30 cm soil and their responses to land use changes. Plant detritus carbon was 6.75 times greater than microbial necromass carbon and dominant across soil depths and ecosystems. Microbial biomass carbon strongly influenced soil organic carbon precursors. Plant detritus carbon exhibited greater sensitivity to land use change than microbial necromass carbon and decomposed preferentially, thus, buffering against fluctuations of the stable soil organic carbon fraction. Our results highlight plant detritus carbon’s key role in maintaining soil organic carbon persistence and suggest that incorporating both residual carbons and land use responses into Earth system models could improve future soil organic carbon projections.