Response of soil microbial quotient to land use change: A global meta-analysis

Soil microbial quotient (SMQ, microbial biomass carbon (MBC)/soil organic carbon (SOC)) is a core indicator for characterizing soil organic matter quality and soil health. However, its response patterns and regulatory mechanisms to land use change (restoration and degradation) lack systematic quantification at a global scale. Based on 134 peer-reviewed articles globally, this study employed meta-analysis to systematically assess the impacts of land use change on SOC, MBC, and SMQ. The results showed that land degradation reduced SOC (-13.4%), MBC (-20.9%), and SMQ (-12.0%); land restoration increased SOC (+73.0%) and MBC (+83.5%), but did not increase SMQ. MBC exhibited a more sensitive and pronounced response to land-use alteration than SOC, and the two variables were positively correlated, verifying that MBC serves as a sensitive indicator for tracking soil carbon dynamics. Furthermore, during the restoration process, the increases in SOC and MBC grew larger with longer restoration duration and decreased with higher initial SOC. The increase in SMQ increased with higher initial SOC and C/N ratio (CNR). During the degradation process, SOC and MBC losses intensified with longer degradation duration and higher initial SOC. The decrease in SMQ slowed with longer degradation duration and higher initial CNR, but intensified with higher initial SOC. Driver analysis revealed that during restoration, duration, initial SOC, and soil depth were the dominant factors driving SOC and MBC responses. During degradation, the core drivers were duration, initial SOC, and CNR. Initial CNR and SOC were common key factors regulating SMQ responses. Overall, this study clarifies the asymmetric response of SMQ to land-use change at the global scale, offering theoretical support for formulating ecological restoration strategies.