Greater contribution of amino sugars to soil organic carbon than glomalin along an elevation gradient in semi-arid mountains

Soil microorganisms play a key role in terrestrial carbon (C) cycling, with microbial residues and glomalin-related soil protein (GRSP) representing stable, microbially derived components of soil organic C (SOC). However, the distribution and contributions of microbial residues and GRSP to SOC in arid mountainous ecosystems remain unclear. This study investigated soil microbial communities, microbial residues, and GRSP, and examined the mechanisms underlying the contribution of amino sugars and GRSP to SOC along an elevation gradient (1848–2940 m) in the Helan Mountains, northwest China. Results showed that with increasing altitude, actinomycete abundance showed no clear trend, while the abundance of other microbial groups and total microbial abundance first increased and then declined. The contents of amino sugar monomers, total amino sugars, microbial residue C, easily extractable GRSP, and total GRSP generally increased with elevation. Similarly, bacterial residue C, fungal residue C, and total microbial residue C increased with altitude, while their relative contributions to SOC declined. The contribution of total GRSP to SOC showed no significant trend, whereas the easily extractable GRSP contribution decreased with elevation. Compared with bacterial (7.21 %), fungal residue C (35.94 %) plays a dominant role in contributing to soil organic C across different altitudinal gradients. Compared with GRSP (4.87 %), microbial residues (43.15 %) accumulated rapidly and contributed more significantly to SOC across the elevational gradient. Variation partitioning analysis revealed that soil physicochemical, microbial community, and vegetation attributes explained 37.15 %, 15.33 %, and 5.48 % of the variation in soil SOC across the elevation gradient, respectively. Variation in microbial residues and GRSP was primarily influenced by soil physicochemical properties, including soil water content (SWC), soil C:phosphorus ratio (C:P), total nitrogen (N), and soil C:N ratio. These findings enhance our understanding of microbial contribution to SOC dynamics and provide insights into microbial-driven SOC stabilization in arid mountainous ecosystems. • Elevation has a significant effect on microbial-derived carbon accumulation. • Microbial residues contribute more to soil organic carbon than glomalin protein. • Fungal residues contribute more to soil organic carbon than bacterial residues. • Elevation regulates microbial necromass carbon through soil water and nutrients.