氮添加对杨树人工林表层土壤微生物群落结构的影响1）

以江苏东台沿海地区杨树人工林地为研究对象，建立野外模拟氮沉降试验样地，试验设置5个氮处理水平，分别为对照（0 kg· hm－2· a－1）、低氮（50 kg· hm－2· a－1）、中氮（100 kg· hm－2· a－1）、高氮（150 kg· hm－2· a－1）和超高氮（300 kg · hm－2· a－1）。于2012年5月开始在生长季（5—10月）每月进行施氮处理，2013年8月和10月运用磷脂脂肪酸法分别分析了土壤微生物群落的变化特征。结果表明，施氮处理近2 a后，两个月份中的土壤微生物磷脂脂肪酸总量均显著下降，细菌、真菌中磷脂脂肪酸的量出现了不同程度的下降，真菌与细菌中磷脂脂肪酸的量之比没有显著变化。磷脂脂肪酸组成的主成分分析显示，除低氮处理样地外，其他水平施氮样地均使微生物群落结构显著变化，且超高氮处理样地变化格局具有季节差异性。

Effects of Nitrogen Addition on Microbial Community Structure in Topsoil of Poplar Plantations

We studied the effects of elevated nitrogen deposition on soil microbial community structure in poplar plantations by phospholipid fatty acid ( PLFA) analysis in August and October 2013.Beginning in May 2012, we conducted a field exper-iment to simulate nitrogen deposition at Dongtai Forest Farm in Jiangsu Province .Nitrogen loadings were designed at five levels of N0 (control), low-N (50 kg· hm-2· a-1), mdeium-N (100 kg· hm-2· a-1), high-N (150 kg· hm-2· a-1), and ultrahigh-N (300 kg· hm-2· a-1).The total PLFAs, the PLFAs of bacteria and fungi decreased to some extent under nitrogen treatment in both months .But the ratios of fungal to bacterial PLFAs was not significantly changed .By principal component analysis ( PCA) for microbial PLFAs data , microbial community structure in all nitrogen treatment sample plots were changed significantly except in the low-N.The pattern of soil microbial changes in ultrahigh-N treatmentplot was not changed in the same way between two months .The decline in total microbial PLFAs and microbial groups (bacteria, fun-gi) with the changes in microbial community structure had substantial impacts on the nutrient cycling within poplar forests ecosystem.