Abstract: Phosphorus (P) is an important limiting nutrient for plant productivity, with a vital role in maintaining forest ecosystem balance. As southern China has become the third largest nitrogen (N) deposition area after Europe and the United States, understanding the effects of increasing N deposition on the transformation of different P fractions in soil is crucial for maintaining plant growth. Cunninghamia lanceolataplantations are important in the subtropics. In this study, we measured soil physicochemical properties, P fraction concentrations, microbial biomass, and phosphatase activity in C. lanceoata plantations by applying control (0 kg N·hm^-2·a^-1), low N (40 kg N·hm^-2·a^-1), and high N (80 kg N·hm^-2·a^-1) treatments. Results showed that N application promoted the transformation between organic and inorganic P, and increased soil NaHCO₃Pi and available P concentrations, thus providing available P for plant growth. Nitrogen application significantly increased microbial biomass P and acid phosphatase activity. A redundancy analysis indicated that soil inorganic P was significantly positively correlated with microbial biomass P and that soil inorganic P was mainly driven by microbial biomass P. Our results provide a reference for the biogeochemical model parameters of soil P transformation in P limited subtropical region in the context of the intensification of N deposition.

Key words: nitrogen application, phosphorus transformation, microbial biomass, acid phosphatase.