[Soil available nitrogen and phosphorus contents and the environmental impact factors across different land use types in typical karst rocky desertification area, Southwest China.]

In this study, we collected soil samples from four different land use types (forest land, shrub land, grassland and abandoned land) in Huajiang valley of Guizhou Province, a typical karst rocky desertification area in Southwest China. Correlation analysis and redundancy analysis were used to examine the distribution of available nitrogen (N) and available phosphorus (P) in diffe-rent soil layers from 0 to 30 cm and the relationships between soil environmental factors (soil physical indexes, organic carbon components, electrochemical properties, metal oxides and enzyme activities) and the contents of available N and available P. The results showed that the concentrations of soil total N, total P, available N, available P decreased significantly with the increases of soil depth. The concentrations of soil available N and available P in forest land and shrub land were significantly higher than those in grassland and abandoned land, which were significantly positively correlated with soil organic carbon composition, enzyme activity, surface electrochemical properties and amorphous mental oxide while significantly negatively correlated with soil silt and free metal oxides. Results of the redundancy analysis showed that the environmental factors affecting soil availa-ble N and available P of the four land use types were basically the same, with soil particulate organic carbon, total organic carbon and soil specific surface area playing a key role in driving the variations of soil available N and available P. The efficient explanation of variation to soil available N and P contents by soil particulate organic carbon might be due to the reduction of soil nutrient loss by the storage of N and P in organic matter. Except for high enzyme activity and electrochemical properties of forest land and shrub land, the higher soil available N and available P concentrations compared with grassland and abandoned land might be resulted from the inhibition of free iron and aluminum oxides information by higher soil organic carbon content and the reduced adsorption and fixation of N and P by iron and aluminum oxides.