Soil organic carbon (SOC):total nitrogen (TN):total phosphorus (TP) (C:N:P) stoichiometry can give important information about biogeochemical cycling in terrestrial ecosystems. The spatial patterns and driving mechanisms of soil C:N:P ratios are still poorly understood on the Qinghai-Tibetan Plateau of China. In this study, we therefore combined data of the geography, climate, soil properties, and vegetation characteristics from 319 sites across the plateau to investigate their relationships with the horizontal and vertical patterns of SOC, TN, and TP concentrations and their stoichiometric ratios (C:N and N:P). We observed higher SOC (30.5–46.8 mg g-1), TN (2.4–3.4 mg g-1), C:N (14.7–18.0), and N:P (6.9–8.0) in alpine meadows, forests, and shrublands and higher TP (1.6 mg g-1) in croplands. Overall, SOC, TN, TP, C:N, and N:P showed decreasing trends (by 67%, 64%, 19%, 12%, and 54%, respectively) along the whole soil profile (0–100 cm). Soil cation exchange capacity and bulk density were the stronger environmental drivers of SOC and TN. Soil TP showed latitudinal and longitudinal increasing trends in all soil layers. Soil properties explained most of the variations in SOC (67%–90%), TN (67%–87%), C:N (61%–89%), and N:P (64%–85%), with increasing impacts along the soil profile. Geography and climate influenced soil TP directly and indirectly through their impacts on soil properties, with geography being the predominant driver (46%–65%) along the soil profile. The variation in soil C:N was mostly driven by SOC and TN, and the direct and indirect effects of the environmental factors were relatively weak. Geography, climate, soil properties, and vegetation characteristics indirectly impacted soil N:P through their impacts on TN and TP in all the soil layers. Altogether, our findings illuminate the relative contributions of geography, climate, soil properties, and vegetation characteristics to soil C:N and N:P, thus enhancing our understanding of C, N, and P cycling across the Qinghai-Tibetan Plateau.
