中文摘要：

在杉木人工林中开展模拟氮沉降试验,设计N0（对照）、N1（60kg N/hm2.a）、N2（120kg N/hm2.a）和N3（240kg N/hm2.a）4种氮沉降水平。通过连续7年的处理后,研究外加氮源对土壤可溶性有机碳及微生物量碳的影响及与土壤酶活性的关系。相同N沉降处理下,土壤有机碳、可溶性有机碳和微生物量碳均随土层加深而降低。氮沉降对土壤有机碳具有促进作用,中-低氮沉降（N1、N2）增加幅度大,高氮沉降（N3）增加幅度小。低氮（N1）处理促进土壤微生物生物量C增加,而中、高氮（N2、N3）则抑制;各氮沉降处理土壤可溶性有机碳含量从高到低的顺序为：N3、N2〉N1〉N0。40-60cm土壤微生物量碳与蔗糖酶、纤维素酶呈极显著正相关关系,与淀粉酶、多酚氧化酶、过氧化物酶呈极显著负相关关系;除40-60cm土层的β-葡糖苷酶外,各层土壤可溶性有机碳与土壤蔗糖酶、纤维素酶和β-葡糖苷酶活性呈极显著正相关关系,与淀粉酶、多酚氧化酶和过氧化物酶呈极显著负相关关系。因此,氮沉降增加将会对土壤碳累积与分解过程产生较大的影响。

英文摘要：

This study evaluated the effects of nitrogen deposition on soil dissolved organic carbon（DOC） and microbial biomass carbon（MBC） in a Chinese fir plantation subject to simulated nitrogen deposition for seven years at Shaxian state forest farm of Fujian province.Nitrogen loadings were designed at 4 levels as N0（control）,N1,N2 and N3 at the doses of 0,60,120,240 kg N/（hm2·a）,respectively.Each treatment comprised three 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.Soil dissolved organic carbon and soil microbial biomass carbon all decreased significantly with the increasing of soil depth at the same level of nitrogen deposition.Nitrogen additions promoted increasing of soil organic carbon,there were highly increasing extents at low-to-moderate nitrogen deposition（N1,N2）,but lowly increasing extents at high nitrogen deposition（N3）.Soil dissolved organic carbon decreased in the sequence of N3,N2 N1 N0.At the soil depth of 40-60 cm,soil microbial biomass carbon was found to be positively correlated with invertase and cellulose,but negatively with amylase,polyphenol oxidase and peroxidase.Except for β-glucosidase at the soil depth of 40-60 cm,soil dissolved organic carbon was also found to be positively invertase,cellulose and β-glucosidase,but negatively with amylase,polyphenol oxidase and peroxidase.Therefore,nitrogen deposition will affect the accumulation and decomposition processes of the soil carbon.