Precipitation and plant cover promote soil organic carbon accumulation in the northeastern Qinghai–Tibet Plateau

Abstract As a core region for global high-altitude carbon cycling, the Qinghai-Tibet Plateau is a key region influencing the regulation of the global terrestrial carbon balance. However, the mechanisms controlling the accumulation of soil organic carbon (SOC) in this fragile ecosystem remain unclear. We surveyed 98 sample sites in the northeastern Qinghai-Tibet Plateau and analyzed the data using Bayesian statistical methods. The 0-20 cm SOC storage on the Qinghai region is about 0.37 Pg. Horizontally, SOC exhibited a decreasing trend from east to west, while vertically, it decreased with increasing soil depth, with a reduction of 24.3%. The result showed that plant cover and mean annual precipitation (MAP) were the dominant positive drivers of SOC accumulation in both soil layers (the 95% credible interval did not overlap with zero). Notably, plant cover and mean annual temperature (MAT) had stronger effects on SOC in the surface layer. The bayesian structural equation model (BSEM) indicated that plant cover, MAP, Shannon diversity index, and the litter C/N ratio collectively explained 68% of the variation in SOC across both layers. The path coefficient (standardized effect size) of MAP on SOC increased with soil depth, whereas that of plant cover decreased, indicating that the influence of environmental factors on SOC accumulation is dependent on depth. These results demonstrate that accurately predicting the Qinghai-Tibet Plateau’s SOC accumulation necessitates the explicit consideration of local plant cover conditions and concurrent precipitation shifts regarding existing SOC accumulation.