Abstract: Nitrogen deposition affects aboveground (such as plant productivity and composition) and belowground properties (such as soil nutrient cycling) in forest ecosystems, with consequences on the structure and function of soil microbial community. We simulated nitrogen deposition at three levels \[N0 (0 kg N·hm^-2·a^-1), N20 (20 kg N·hm^-2·a^-1), N80 (80 kg N·m^-2·a^-1)\] in a Phyllostachy pubescens forest in Daiyun Mountain in subtropical China for three years. We measured soil physicochemical properties, humification index, and microbial phospholipid fatty acids to clarify how nitrogen addition affects soil nutrients and microbial community structure in P. pubescens forest. The results showed that N20 treatment significantly increased soil humification index, reduced total content of alkaline cations (K⁺, Na⁺, Ca²⁺, Mg²⁺), Grampositive bacteria (G⁺), Gram-negative bacteria (G^-), total phospholipid fatty acids (total PLFAs), and the ratio of G⁺/G^-. Compared to N20 treatment, N80 treatment significantly increased the contents of soil nitrate, G⁺, G^-, total PLFAs and G⁺/G^-(P<0.05). Results of correlation analysis showed that soil humification index was negatively correlated with soil microbial biomass. Results of redundancy analysis showed that the total amount of alkaline cations and available nitrogen were important environmental factors driving the changes of microbial community structure. Our results indicated that nitrogen addition may change soil microbial nutrient requirements in the P. pubescens forest, which in turn affects soil microbial community structure.

Key words: air quality, diffusion simulation, development trend., street canyons