Hydrothermal and Vegetation-Mediated Controls on Soil Organic Carbon in an Alpine Headwater Region of the Tibetan Plateau: Implications for Sustainable Grassland Management

Soil organic carbon (SOC) is essential for ecosystem stability and long-term carbon storage in alpine grasslands, yet the relative importance and interactions of hydrothermal and biotic controls remain poorly understood at regional scales. In this study, we quantified surface SOC (0–20 cm) across the Yellow River Source Region (YRSR) on the northeastern Tibetan Plateau, a climate-sensitive alpine headwater system characterized by strong hydrothermal gradients and freeze–thaw dynamics. Field-based SOC measurements were integrated with multi-source remote sensing and reanalysis data that describe thermal conditions, moisture processes, vegetation productivity, soil properties, topography, and human influence. A two-step screening approach was applied using Boruta and variance inflation factor filtering, followed by modeling with random forest. The model outputs were interpreted using Shapley Additive Explanations (SHAP). SOC displayed significant spatial heterogeneity across the region. Vegetation productivity, moisture availability, and thermal conditions were identified as the dominant nonlinear drivers of SOC variation. Moisture availability emerged as a central regulator of SOC, affecting it both directly and indirectly through vegetation productivity and thermal conditions. These findings underscore the importance of hydrothermal stability in sustaining soil carbon stocks and provide a quantitative basis for adaptive grassland management under a warming climate.