Climate–Plant–Soil Linkages Regulate the Response of Soil Organic Carbon and Its Active Fractions to Grassland Degradation on the Qinghai‐Tibetan Plateau: A Meta‐Analysis

Anthropogenic activities and climate change have led to substantial grassland degradation, which can profoundly affect ecosystem carbon (C) cycling. However, the impact of degradation on soil organic carbon (SOC) and its active fractions on the Qinghai‐Tibetan Plateau (QTP) remains unclear. Here, a meta‐analysis of 417 soil profile datasets (0–100 cm) from 40 experimental studies was conducted to examine the alterations in SOC and its active fractions in alpine grasslands on the QTP following degradation. The results indicated that degradation led to a 51.33% decrease in SOC and its active fractions: particulate organic carbon (POC) decreased by 59.18%, easily oxidized organic carbon (EOC) by 51.05%, light fraction organic carbon (LFOC) by 40.10%, microbial biomass carbon (MBC) by 34.30%, and dissolved organic carbon (DOC) by 30.96%. Degradation reduced aboveground biomass, resulted in decreased C input and heightened soil erosion, culminating in an enhanced loss of DOC. In comparison to steppes, alpine meadows exhibit a superior ability for C retention. DOC and EOC decreased at a higher rate in the mixed C 3 –C 4 grassland compared to the C 3 ‐dominated grassland. Degradation decreased soil nitrogen and phosphorus content, prompting microbes to accelerate the SOC decomposition, which led to a decline in EOC and POC. Soil depth may diminish the sensitivity of active C to degradation responses, particularly MBC and LFOC, likely because higher soil moisture levels and fostering more favorable conditions for microbes in deeper soil layers. The negative effect of degradation on SOC active fractions decreased when MAT ≥ 1°C and MAP > 700 mm, due to a prolonged growth season thus boosted photosynthesis. The rates of C loss were notably higher at elevations ≤ 3800 m. Our results can contribute to an in‐depth understanding of soil C dynamics following degradation, and offer a conceptual framework for managing grassland C pools.