[Responses of soil phosphorus fractions and microorganisms to nitrogen application in a subtropical Phyllostachys pubescen forest]

Phosphorus (P) is an important nutrient for plant and microbial growth. Soil P availabi-lity is poor in subtropical areas. Long-term heavy nitrogen (N) deposition might further reduce P availability. The experiment was performed in a Phyllostachys pubescens forest in Daiyun Mountain. The effects of N application on soil basic physical and chemical properties, soil P fractions, microbial biomass, and acid phosphomonoesterase activity were analyzed after three years of N application. The results showed that N application significantly increased NO₃^--N content and thus soil N availability, while it significantly reduced the percentage of decomposable organic P to total P, with the ratio of carbon (C) to organic P being over 200. The soil microbial biomass C, microbial biomass P, acid phosphomonoesterase, and the ratio of microbial biomass N to microbial biomass P and microbial biomass C to microbial biomass P were increased as the N application rate increased. There was a significant negative correlation between the percentage of decomposable organic P to total P and microbial biomass P. Consequently, N application enhanced soil P limitation and increased microbial P demand.