Abstract: Fine root is critical in the belowground carbon (C) cycling in forest ecosystem. Aimed to understand the effects of nitrogen (N) deposition on the fine root characteristics and soil respiration in Pleioblastus amarus plantation, a two-year field experiment was conducted in the Rainy Area of West China. Four treatments with different levels of N deposition were installed, i.e., CK (0 g N·m^-2·a^-1), low N (5 g N·m^-2·a^-1), medium N (15 g N·m^-2·a^-1), and high N (30 g N·m^-2·a^-1). There were great differences in the biomass and element contents of <1  mm and 1-2 mm fine roots among the treatments. Comparing with < 1 mm fine roots, 1-2 mm fine roots had higher contents of lignin, P, and Mg, but lower contents of cellulose and Ca. Nitrogen deposition increased the biomass of < 2mm fine roots significantly, with the values being (533±89) g·m^-2 in CK, and (630±140), (632±168), and (820±161) g·m^-2 in treatments low N, medium-N, and high N, respectively. The N, K, and Mg contents of <2 mm fine roots also had an obvious increase under N deposition. The annual soil respiration rate in treatments CK, low N, medium N, and high N was (5.85±0.43), (6.48±0.71),(6.84±0.57), and (7.62±0.55) t C·hm^-2·a^-1, respectively, indicating that N deposition had obvious promotion effects on soil respiration. There were significant linear relationships between the annual soil respiration rate and the biomass and N content of <2 mm fine roots. N deposition increased the fine root biomass and promoted the root metabolism, and stimulated the rhizospheric soil respiration rate via promoting microbial activities.

Key words: nitrogen deposition, soil respiration, rhizospheric soil respiration, fine root, Pleioblastus amarus plantation, Rainy Area of West China, growth strategy, morphological characteristics, nutrient absorption, Phyllostachys rivalis,  rhizome and root system, waterlogging.