Abstract: Glomalin-related soil protein (GRSP) is a complex microbial-derived glycoprotein mixture that acts as an essential bio-glue stabilizing organic carbon (C) pools and driving soil aggregation and C sequestration. Yet, how divergent bedrocks (lithology) and rock-soil interfaces govern GRSP accrual in karst forest ecosystems remains poorly understood. Here, we investigated GRSP accrual at rock-soil interfaces and adjacent bulk soils across limestone and dolostone in Southwest China. GRSP contents at the rock-soil interface significantly surpassed those in corresponding bulk soil, irrespective of lithology. GRSP_T contents and their contributions to soil organic carbon (SOC) were consistently higher in limestone than in dolostone. Mantel’s test and regression analysis demonstrated strong correlations between GRSP accrual and microbial diversity (Viruses_α; Bacteria_α), biomass (MBC; MBN), ecoenzymatic C:N stoichiometry (E_C:N), soil mineral protection ((Ca+Mg)_e; (Fe+Al)_o), and labile N (DON; NH₄⁺). Random forest modeling confirmed microbial biomass as the key driver of GRSP accumulation, followed by mineral protection, microbial diversity, labile N, and ecoenzymatic stoichiometry. Structural equation modeling revealed that lithology and rock-soil interface facilitated GRSP formation and stabilization by enhancing N availability, mineral protection, microbial diversity, and biomass. We proposed the “Roccosphere” concept to delineate the rock-soil interface as a distinct microhabitat shaped by bedrock weathering and microbial activity in karst regions, analogous to the “Rhizosphere” and “Hyphosphere”. These findings highlight the vital influence of lithology and the rock-soil interface on GRSP accrual via microbial and mineral C pumps, with implications for soil C sequestration and vegetation restoration in degraded karst forest ecosystems.

Key words: SOC sequestration, bedrock weathering, microbial traits, reactive minerals, microbial nutrient limitation