Climate factors regulate the depth dependency of soil organic carbon under grazing exclusion in Chinese grasslands: A meta‐analysis

Abstract Soil carbon (C) is one of the most abundant C pools in terrestrial ecosystems, and its dynamics is highly dependent on soil depth. Grazing exclusion (GE) has proven to be a promising approach for enhancing C sequestration; however, the comprehensive analysis on the depth distribution of soil C and driving factors of soil C dynamics under GE are still lacking. This study collected data comprising 563 paired observations from 75 papers to analyze the distribution characteristics and the driving factors of soil organic carbon (SOC) changes with soil depth under GE in Chinese grasslands. The results showed that GE positively contributed to soil C sequestration, and the change range of SOC were higher (47.70%) in the subsoil (>20 cm) than in the topsoil layer (0–20 cm; 29.24%). Furthermore, SOC was influenced by GE duration, exhibiting an increasing trend and reaching its highest value at 13–15 years of GE, then remaining stable or slightly decreasing thereafter. Boosted regression trees (BRTs) showed that climatic factors were the primary determinants of SOC changes; however, the key drivers of SOC varied across different soil depths. Mean annual precipitation (MAP) was the key driver of topsoil C dynamics, accounting for 32.7% of the variance. In contrast, mean annual temperature (MAT) regulated the response of subsoil SOC to GE, explaining 48.23% of the variance. In addition, plant biomass was a significant factor influencing the depth distribution of soil C under GE, and its effect on SOC decreased with increasing soil depth. Our study provides evidence that the subsoil has a greater potential for C sequestration than the topsoil layer after GE, and future studies should consider deep soil C dynamics to accurately assess C sequestration in grassland ecosystems.