模拟氮沉降对华西雨屏区苦竹林细根特性和土壤呼吸的影响

细根在森林生态系统地下碳循环过程中具有核心地位.2007年11月-2009年11月，对华西雨屏区苦竹人工林进行了模拟氮沉降试验.氮沉降水平分别为对照(CK,0 g N·m^-2·a^-1)、低氮(5 g N·m^-2·a^-1)、中氮(15 g N·m^-2·a^-1)和高氮(30 g N·m^-2·a^-1)处理，研究氮沉降对苦竹人工林细根和土壤根际呼吸的影响.结果表明：不同处理氮沉降下，<1 mm和1～2 mm细根特性差异较大，与< 1 mm细根相比，1～2 mm细根的木质素、磷和镁含量更高，而纤维素、钙含量更低；氮沉降显著增加了<2 mm细根生物量,对照、低氮、中氮和高氮处理的细根生物量分别为(533±89)、(630±140)、(632±168)和(820±161) g·m^-2,氮、钾、镁元素含量也明显增加；苦竹林各处理年均土壤呼吸速率分别为(5.85±0.43)、(6.48±0.71)、(6.84±0.57)和(7.62±0.55) t C·hm^-2·a^-1，氮沉降对土壤呼吸有明显的促进作用；苦竹林的年均土壤呼吸速率与<2 mm细根生物量和细根N含量呈极显著线性相关.氮沉降使细根生物量和代谢强度增加，并通过增加微生物活性促进了根际土壤呼吸.

Effects of simulated nitrogen deposition on the fine root characteristics and soil respiration in a Pleioblastus amarus plantation in Rainy Area of West China

Fine root is critical in the belowground carbon (C) cycling in forestecosystem. 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. Fourtreatments 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.