Distributions and Drivers of Soil Organic Carbon on the Tibetan Plateau: Divergent Controls Across Ecosystems

Background The Tibetan Plateau (TP), a vast alpine region with substantial soil organic carbon (SOC) stocks, plays a crucial role in the regional carbon cycle and climate change mitigation. However, our understanding of the spatial distribution and underlying drivers of SOC across TP remains limited. Methods We quantified the horizontal (1 km resolution) and vertical (0–200 cm depth) patterns in SOC density (SOCD) across the TP using 1,561 soil samples and a fully trained and validated Random Forest (RF) model. Twenty-six environmental variables were evaluated to determine their influence on SOCD. Correlation analysis and Structural Equation Modeling (SEM) were employed to examine the associations and causal mechanisms between these factors and SOCD. Results SOCD decreased from east to west and south to north, with mean values of SOCD ranging from 14.96 kg C m⁻² in western steppes to 29.54 kg C m⁻² in eastern forests at 0-200 cm depth. Vertically, SOCD exhibited a nonlinear pattern, initially increasing and then decreasing with depth. SOCD was highest in wetlands, followed by forests, meadows, shrublands, and steppes. Conclusions SOCD was influenced by multiple interacting environmental factors, primarily through their effects on plant productivity and soil respiration. Different ecosystems exhibit distinct regulatory mechanisms for SOCD. Forests are dominated by carbon loss through respiration, while grasslands and other ecosystems rely more on plant-derived carbon inputs. These findings enhance our understanding of distinct mechanisms regulating soil organic carbon across ecosystems, supporting improved modeling of soil carbon-climate feedbacks and informing ecosystem-specific carbon management strategies.