Projecting future soil organic carbon and soil total nitrogen stocks under climate-land use change scenarios in Tibet, China

Soil organic carbon (SOC) and soil total nitrogen (STN) serve as critical indicators of climate-mediated ecosystem processes and constitute essential components of terrestrial biogeochemical cycling. Quantifying the ecological consequences of land use change on SOC and STN stocks is fundamental for developing sustainable resource management strategies. In this study, we integrated 105 topsoil samples (0–30 cm) with nine environmental variables — derived from topographic, climatic, and human activity datasets — to construct boosted regression tree (BRT) models for predicting the spatial distribution of SOC and STN stocks in 2018. Model performance was rigorously evaluated through 10-fold cross-validation, demonstrating robust predictive accuracy as evidenced by R 2 and Lin's concordance correlation coefficient values, coupled with mean absolute error and root mean square errors. Our analysis identified mean annual precipitation and catchment characteristics as the predominant drivers of SOC and STN spatial variability. To project future dynamics under climate and land use change scenarios (2050s and 2090s), we applied the space-for-time substitution (STS). The results revealed divergent trajectories: under both SSP245 and SSP585 scenarios, SOC stocks were projected to declined by 1163 Tg and 1171 Tg, respectively, by the 2050s relative to 2018 baselines, with concurrent STN reductions of 64 Tg (1 Tg = 10 9 kg) each. By the 2090s, SSP245 scenarios indicated partial recovery (SOC +1161 Tg, STN +63 Tg), whereas SSP585 projected continued depletion (SOC -1046 Tg, STN -57 Tg). Notably,grasslands and forests ecosystems collectively maintained approximately 80 % of regional SOC and STN stocks across both temporal intervals, underscoring their conservation importance. This study highlights the imperative of integrating climatic variability into SOC/STN stock assessments. The high-resolution spatial mapping developed herein provides actionable insights for optimizing soil management practices and strengthening ecosystem resilience in Tibet under evolving climatic conditions. • MAP and CA as key influencing factors affected SOC and STN stocks. • Future projections show significant reductions in SOC and STN by the 2050s. • Grasslands and forests together hold 80 % of the region's SOC and STN stocks.