Abstract:Biocrusts (biological soil crusts), as ubiquitous living covers on soil surface of the revegetated grasslands in hilly regions of the Loess Plateau, are potential influence factors on the availability of soil P (phosphorus). However, researches focus on the relationship between soil P availability and development of biocrusts were still fresh so far. Impacts of biocrusts on soil total P, available P and phosphatase activity were investigated in revegetated grasslands at different stages of biocrusts developed after the survey of biocrusts distribution. The objects of the study were to determine the influences of biocrusts development on the availability of soil P in the region. The results show that the biological crusts could significantly improve soil total phosphorus contents in the biocrusts layers, while the contents of total phosphorus in 0-10 cm layers are not significant. Soil available phosphorus contents of the biocrusts in the study area are in the range of 3.27-5.87 mg/kg, which are accounting for 0.57%-0.95% of total P in the same layer. The alkaline phosphatase activities in biocrusts are significantly higher than those of the lower soils (0-10 cm) 3-81 times. The effects of biological crusts on the availability of soil P and phosphatase activity are related to the developmental stages of biocrusts. The biological crusts increase alkaline phosphatase activity and organic matter, and reduce the crusts on soil pH, finally improve the availability of soil phosphorus. These results suggest that the availability of soil P could be significantly enhanced for the formation of biocrusts.