Distributions pattern of phosphorus, potassium and influencing factors in the upstream of Shule river basin

Soil phosphorus (P) and potassium (K) are indispensable elements of plant growth, and their content change could affect biogeochemical cycles of carbon, nitrogen, and other elements. The study of spatial and vertical distributions of soil P and K is crucial for the sustainable development of alpine grassland. Further, it is critical to understand regional mechanisms of biogeochemical cycles of soil carbon, nitrogen, and other elements. Thirteen typical ecosystem plots (including seven soil types) were selected, and two or three soil profiles from each plot were investigated. This study occurred during the summers of 2010 and 2011 in the upstream of the Shule river basin on the northeastern margin of the Qinghai-Tibetan Plateau. Distributions of soil P and K, their influencing factors on topsoil (0-20 cm), and the soil profiles were studied. These elements were studied by analysis of soil P and K contents, other soil properties (such as soil organic carbon, total nitrogen, pH value, and so on), and meteorological factors (mean annual temperature and mean annual precipitation). The results showed that soil total P, available P, total K, and available K contents in topsoil were (0.50 plus or minus 0.14) g/kg, (2.69 plus or minus 1.61) mg/kg, (14.84 plus or minus 0.59) g/kg, and (151.03 plus or minus 117.57) mg/kg, respectively. The correlation matrix of the variables showed that there were significant positive correlations between total P contents in the topsoil, mean annual temperature, and soil silt proportions. However, there was a significant negative relationship between total P contents in the topsoil and mean annual precipitation. Meanwhile, there were significant positive relationships between available P, soil organic carbon, and total nitrogen. There was a significant positive relationship between soil available K, soil silt content, and mean annual temperature. The densities of total P, available P, total K, and available K mainly concentrated in the 0-40 cm soil depth, and showed a decreasing trend with soil depth increase. Total P densities at different soil depths had a positive correlation with mean annual temperature, which increased with soil depth. Our study indicated that air temperature and precipitation were the main influencing factors for soil total P contents in topsoil and its spatial distribution. Because of similar soil parent material, small variances of total K in topsoil for the seven soil types were observed. The content of avai