Optimal Grazing Exclusion Duration to Enhance Soil Carbon Sequestration in Degraded Grasslands.

Soil organic carbon (SOC) plays a crucial role in mitigating climate change and ensuring food security. Grazing exclusion (GE) is widely recognized as an effective strategy for restoring degraded grasslands and enhancing SOC sequestration, yet the optimal duration for this practice remains uncertain. Here, we conducted a meta-analysis using 4257 paired observations from 125 studies in China to quantify the impact of GE on SOC content and stock, and to determine the optimal duration for maximizing carbon sequestration. We found that GE increased SOC content and stock by an average of 34.12% and 24.56%, respectively. This positive effect of GE on SOC becomes greater over time in areas with higher mean annual precipitation (MAP), but it is negative below 200 mm. These effects of GE remain consistent across alpine, meadow, desert, and typical grasslands, and are independent of other environmental attributes. Our results indicate that implementing GE on 70% of degraded grasslands nationwide could, on average, sequester 1.52 Pg C in soil over a period of 10 years (about 17% of global annual fossil fuel emissions), with larger gains expected in higher-MAP regions. Our synthesis provides an evidence-based framework for optimizing grassland restoration through enhanced soil carbon sequestration in degraded grasslands.