Bedrock geochemistry regulates glomalin-related soil protein accrual in subtropical karst forest soils, Southwest China

Lithology-driven changes in forest soil nutrients have a strong impact on glomalin-related soil protein (GRSP). GRSP is a key component of the stable microbial-derived carbon (C) pools in soil and plays an important role in promoting the accumulation and stability of soil organic carbon (SOC). However, the influence of lithology on GRSP content and its contribution to SOC in subtropical karst forest ecosystems remains unclear. To address this, we quantified the GRSP contents in the topsoil (0-15 cm) of forest ecosystems overlying karst (limestone (LR); dolostone (DR)), and non-karst (clasolite (CR)) in Southwest China. Our results demonstrated that lithology exerted a significant control on total GRSP (GRSP(T)) accumulation and its contribution to SOC (GRSP(T)/SOC). GRSP contents were significantly higher in DR and LR soils compared to CR soils, whereas GRSP(T)/SOC exhibited an inverse trend. Furthermore, GRSP(T) displayed strong positive correlations with SOC, fungi alpha-diversity (Fungi(alpha)), bacteria alpha-diversity (Bacteria(alpha)), soil mineral protection ((Ca + Mg)(exe)/(Fe + Al)(o); Clay + Silt), nitrogen (N) status (soil total N (STN); soil mineral N (SMN)), and rock Ca content (Ca-rock), but was negatively correlated with microbial ecoenzymatic stoichiometry (BG/(LAP + NAG); BG/AP) and rock weathering index (CIA) (p < 0.001). Random forest analysis identified microbial diversity as the predominant driver of GRSP(T), followed by soil mineral protection and ecoenzymatic stoichiometry. Structural equation modeling revealed that lithology-driven geochemical processes (e.g., rock weathering and mineral protection) indirectly regulated GRSP accrual via microbial functional traits. These findings shed light on the lithology-dependent regulation of GRSP dynamics and its pivotal roles in SOC sequestration, enhancing our capacity to predict and manage SOC storage within degraded karst forest ecosystems. These findings also simultaneously establish a foundation for research on Nature-based Solutions (NbS) in karst forests grounded in ecological restoration. Through approaches such as ecological restoration, NbS can enhance C sequestration mediated by GRSP, thereby contributing to the restoration and conservation of subtropical karst forest ecosystems.