Decoupling of soil nitrogen and phosphorus dynamics along a temperature gradient on the Qinghai-Tibetan Plateau

Abstract Responses of soil nitrogen (N) and phosphorus (P) dynamics to global warming have received much attention. However, there are a lot of uncertainties. Given that a large-scale field investigation along a temperature gradient can provide deep insight into the long-term effect of climate warming, we conducted a soil sampling along a temperature gradient across a 1500-km transect on the Qinghai-Tibetan Plateau. To minimize the interference of the collinearity between temperature and precipitation on the temperature patterns of soil N and P dynamics, the sampling was performed along the 400 mm isohyet. We wanted to clarify the alterations of soil N and P dynamics in response to increasing temperature when the precipitation effect was minimized. Soil N content and N storage decreased, whereas soil P content and P stocks were stable with increasing temperature, leading to a decreased soil N:P ratio along the temperature gradient. This means that soil N and P dynamics are decoupled under the condition of increasing temperature. Soil N dynamics were associated with the variations in soil organic matter content, silt content, pH and vegetation type, and the effect of temperature on soil N dynamics was mainly through the influence of temperature on soil organic matter content. Soil P dynamics were related to the changes of soil silt content, precipitation, vegetation and soil type. Our results suggest that global warming may negatively affect soil N dynamics, but have no or only a small effect on soil P dynamics, and at the same time may cause the ecosystem to change from P limited to N limited.