Spatiotemporal Dynamics of Soil Organic Carbon in the Qinling Mountains and Its Responses to Future Climate Change

Soil organic carbon (SOC) is pivotal to the terrestrial carbon cycle and climate regulation, yet its spatiotemporal dynamics and future climate responses across soil layers remain insufficiently understood in mountainous ecosystems. Taking the Qinling Mountains, a typical mountainous ecological barrier in central China with a total area of approximately 38.18 × 104 km2, as the study area, we analyzed historical SOC changes (1980s–2010s) and projected its future dynamics under different scenarios using a validated Random Forest model (R2 = 0.81 for 0–20 cm, SOC20; 0.73 for 0–100 cm, SOC100), and further disentangled dominant drivers. Results showed historical mean SOC density increased, with higher storage in western/central high-elevation zones and lower values in southern/eastern low-elevation areas. Climate was the primary driver of SOC20 dynamics, while SOC100 was jointly regulated by climate, vegetation, and environmental factors, indicating weakened climatic control with increasing soil depth. Precipitation increases partially offset warming-induced SOC loss, leading to small changes in regional mean SOC density, but strong spatial heterogeneity resulted in substantial total SOC stock losses (SOC20: −1.41 to −6.59 Tg C; SOC100: −6.86 to −28.76 Tg C), with net losses in high-elevation zones and gains in low-elevation areas. SOC within the whole 1 m soil profile exhibited larger climate-driven changes than topsoil. These findings advance understanding of SOC dynamics in complex mountainous ecosystems and provide key scientific insights for regional carbon cycle assessments under climate change.