Effects of nitrogen deposition on soil microorganism were evaluated in a Chinese fir plantation subjected to simulated nitrogen deposition for seven years at Shaxian State Forest Farm of Fujian Province, China. Nitrogen loadings were designed at 4 levels as NO (control), N1 , N2 and N3 at the doses of 0, 60, 120 and 240 kg·hm-2a-1N, respectively. Low nitrogen deposition ( N1 ) promoted soil microbial biomass, microbial activity, and ability of carbon source utilization by microbes, but intermediate and high nitrogen deposition (N2, N3) showed the opposite effect. All kinds of nitrogen deposition were able to influence microbial community functional diversity. The low nitrogen deposition increased the richness and evenness of microbial community, while the intermediate and high nitrogen deposition reduced these parameters. Principal component analysis ( PCA) in substrates indicated that the main carbon sources for soil microbes were carbohydrates and carboxylic acid in all treatments and there were significant differences in carbon substrate utilization patterns between treatments. Our results indicated that functional diversity of soil microbes was altered by nitrogen deposition and the ability of microbes to utilize carbon source and the type of carbon sources were affected by different nitrogen deposition intensities.%在杉木人工林中开展N0(对照),N1(60 kg N·hm-2a-1),N2(120 kg N·hm-2a-1)和N3(240 kg N·hm-2a-1)4种水平氮沉降模拟试验,连续处理7年后,探讨外加氮源对土壤微生物的影响.结果表明:各土层中,低氮处理(N1)可增加土壤微生物生物量碳含量、微生物生物活性和微生物群落碳源利用能力,而中、高氮处理(N2和N3)则呈抑制作用；低氮处理(N1)能提高土壤微生物Shannon-Wiener多样性指数与均匀度指数,而中、高氮处理使指数降低；主成分分析结果表明,土壤微生物群落利用的主要碳源为碳水化合物和羧酸,不同氮沉降处理土壤微生物群落利用的的碳源类型存在较大差异.
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