Impacts of geography, climate, soil properties and vegetation characteristics on soil C:N:P stoichiometry across the Qinghai-Tibetan Plateau

Soil C:N:P (soil organic carbon: total nitrogen: total phosphorus) stoichiometry can give important information about biogeochemical cycling in terrestrial ecosystems. The spatial patterns and driving mechanisms of soil C:N:P stoichiometry are still poorly understood on the Qinghai-Tibetan Plateau. In this study, we therefore combine data on the geographic position, climate, soil properties and vegetation characteristics of 319 sites across the plateau to investigate their relationship with the horizontal and vertical patterns of soil C, N and P concentrations and the C:N:P ratios. We observed higherSOC (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 with an amplitude of 67%, 64%, 19%, 12% and 54% respectively along the soil profile. Soil cation exchange capacity (CEC) 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. Geographical position and climate influenced TP both directly and indirectly through soil properties, with geographical position being the predominant driver (46%–65%) along the whole 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. Geographical position, climate factors, soil properties and vegetation indirectly impacted soil N:P through their effects on soil TN and TP in all the soil layers. Altogether, our findings shed important light on the relative contribution of geography, climate, vegetation and soil properties on soil C:N and N:P, thus providing a better understanding of C, N, and P cycling across the Qinghai-Tibetan Plateau.