中文摘要：

2007--2008年，采用氯仿熏蒸浸提法测定了落叶松和水曲柳人工林土壤微生物生物量，研究施N肥对土壤微生物生物量碳、氮，以及细菌、真菌和放线菌数量季节变化的影响．结果表明：落叶松林地土壤微生物生物量碳、氮两年平均值分别比水曲柳林地低13．8％和18．3％，但两种林分土壤微生物生物量碳、氮具有相同的季节变化规律：5月最低，9月最高；表层（0～10cm）土壤微生物生物量碳、氮及微生物数量均高于亚表层（10～20cm）土壤．但细菌、真菌和放线菌数量的季节变化格局与生物量不同．施肥降低了两种林分的微生物生物量碳、氮，以及细菌、真菌和放线菌数量，其中，落叶松林地微生物生物量碳和氮分别降低了24％和63％，水曲柳分别降低了51％和68％．说明施N肥限制了土壤微生物生物量，改变了土壤微生物的群落结构．

英文摘要：

This paper studied the seasonal dynamics of soil microbial biomass C （Cmic ） and N （ Nmic ）, and of bacteria （ cfub ）, fungi （ cfuf）, and actinomyces （ cfu ） in Larix gmelinii and Fraxinus mandshurica plantations in 2007-2008 under N fertilization. The two-year averaged soil Cmic and Nmic in L. gmelinii plantation were 13.8% and 18.3% lower than those in F. mandshurica plantation, respectively, but the soil Cmic and Nmic in the two plantations had similar seasonal patterns, being the lowest in May and the highest in September. The Cmic and Nmic, and the cfub, cfuf, and cfua were all greater in topsoil （0-10 cm） than in subsoil （10-20 cm）, but the seasonal patterns of cfub, cfuf, and cfua were different from those of Cmic and Nmic. N fertilization decreased the Cmic and Nmic, and the cfub, cfuf, and cfua significantly, with the decrements of Cmic and Nmic being 24% and 63% in L. gmelinii plantation, and 51% and 68% in F. mandshurica, respectively, which suggested that N fertilization limited soil microbial biomass and altered soil microbial communities in the two plantations.