Alterations in soil pH drive the impact of global change on glomalin-related soil protein: a global meta-analysis

Glomalin-related soil protein (GRSP), a key glycoprotein metabolite of arbuscular mycorrhizal fungi (AMF), plays a central role in soil carbon and nitrogen sequestration and aggregate stability. However, a systematic understanding of its response patterns and driving mechanisms under diverse global change factors (GCFs) remains limited. This study conducted a global meta-analysis to assess the effects of 14 GCFs (including land-use conversion, fertilization, and climate change) on the two GRSP fractions: easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP). The results demonstrated that T-GRSP exhibited more pronounced responses to GCFs than EE-GRSP, making it a superior indicator for characterizing long-term changes. Specifically, fertilization (nitrogen +28%; phosphorus +12%; nitrogen and phosphorus +44%; nitrogen, phosphorus and potassium +33%) and elevated CO₂ (eCO₂ +7%) significantly promoted T-GRSP accumulation (all relative to control, p < 0.05). In contrast, land-use conversions such as forest to bare land (-91%), farmland (-33%), shrubland (-36%), and grassland to farmland (-43%) significantly reduced T-GRSP. Warming, fire, and forest-to-grassland conversion showed no significant effects. Soil pH change was identified as the pivotal hub regulating GRSP responses to GCFs, governing GRSP accumulation dynamics by influencing its mineral adsorption and microbial decomposition. Furthermore, changes in T-GRSP were tightly coupled with soil organic carbon (SOC) and total nitrogen (TN), directly contributing to the stable C and N pool and indirectly enhancing physical protection through promoting aggregate formation. Notably, under climate change, the relationship between SOC, TN and T-GRSP showed "decoupling". Concurrently, a significant negative correlation emerged between the proportion of T-GRSP in SOC, TN and their actual contents, revealing an adaptive strategy in which T-GRSP serves as a stable component for "core protection". This study systematically elucidates the response patterns and mechanisms of GRSP to global change, highlighting its dual role in maintaining the stability of soil carbon and nitrogen pools.