模拟氮沉降对杉木人工林(Cunninghamia lanceolata)土壤酶活性及微生物群落功能多样性的影响

Effects of Simulated Nitrogen Deposition on Soil Enzyme Activities and Microbial Community Functional Diversities in a Chinese Fir Plantation

在杉木人工林中开展模拟氮沉降试验,设计N0(对照)、N1(N 60 kg/(hm2.a))、N2(N 120 kg/(hm2.a))和N3(N 240 kg/(hm2.a))等4个氮沉降水平。通过连续7年的处理后,研究了外加氮源对土壤酶活性及群落功能多样性的影响。相同氮沉降处理下,参与土壤碳循环的6种主要酶(蔗糖酶、纤维素酶、淀粉酶、β-葡糖苷酶、多酚氧化酶、过氧化物酶)活性、土壤微生物群落碳源利用能力和多样性指数与均匀度指数均随土层加深而降低。氮沉降对纤维素酶和多酚氧化酶具有促进作用,而对淀粉酶和过氧化物酶表现出一定的抑制作用;中?低氮沉降(N1、N2)对蔗糖酶无影响,而对β-葡糖苷酶具有促进作用,高氮沉降(N3)促进了蔗糖酶活性,但抑制了β-葡糖苷酶活性。各土层中,低氮处理(N1)促进了微生物群落碳源利用能力和多样性指数与均匀度指数的增加,而中?高氮处理(N2、N3)则呈抑制作用。主成分分析表明,土壤微生物群落利用的主要碳源为碳水化合物和羧酸,不同氮沉降处理碳源利用类型存在差异。因此,氮沉降促进了表层土壤纤维素酶、多酚氧化酶和蔗糖酶的活性,但在一定程度上抑制了淀粉酶、过氧化物酶和β-葡糖苷酶活性;氮沉降增加改变了杉木人工林土壤微生物群落的功能多样性。

This study evaluated the effects of nitrogen deposition on soil enzyme activities and microbial community functional diversities （sole-source carbon utilization, SCU） in a Chinese fir plantation subject 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 （CK）, N1, N2 and N3 at the doses of 0, 60, 120 and 240 kg/（h㎡·a）N, respectively. Each treatment comprised 3 replicate plots of 20 m×20 m which were sprayed with CO（NH2）2 solutions on the forest floor at the beginning of each month, lasting from January 2004 to the sampling time, March 2010. At the same level of nitrogen deposition, the activities of 6 soil enzymes involving carbon cycle （invertase, cellulose, amylase, β-glucosidase, polyphenol oxidase and peroxidase）, the ability of carbon source utilization by microbe, biodiversity and evenness all decreased with the increase of soil depth. At soil depth of 0-20 cm, nitrogen additions promoted cellulose and polyphenol oxidase activities, but inhibited amylase and peroxidase to some extents. High level of nitrogen loading （N3） showed significant positive impact on invertase, but negative on β-glucosidase. Low nitrogen deposition （N1） accelerated the ability of carbon source utilization by microbe, biodiversity and evenness, but moderate-to-high nitrogen deposition （N2, N3） gave the opposite effect. 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 of carbon substrate utilization patterns between treatments. Hence, nitrogen deposition in this experiment accelerated the activities of surface soil cellulose, polyphenol oxidase and invertase, but inhibited amylase, peroxide and β-glucosidase to some extents. Nitrogen deposition produced significant impacts on the functional diversity of soil microbial community in the Chinese fir plantation.