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在杨树人工林中,采用随机区组设计、野外定位模拟氮沉降试验,研究氮沉降对土壤微生物群落结构的影响。设计5个氮沉降水平,分别为:空白对照N0(0 kg·hm-2·a-1)、低氮N1(50 kg·hm-2·a-1)、中氮N2(100 kg·hm-2·a-1)、高氮N3(150 kg·hm-2·a-1)、超高氮N4(300 kg·hm-2·a-1)。从2012年5月开始在生长季(5—10月)每月进行施氮处理。施氮2年后,运用磷脂脂肪酸(PLFA)方法对0~10 cm土层中的微生物群落结构进行了测定。结果表明,施氮处理未改变微生物PLFAs总量水平,但使细菌和革兰氏阳性细菌PLFAs含量上升;中氮处理使真菌PLFAs含量显著下降,其他水平的氮处理对其影响则不显著;中氮、高氮和超高氮处理使丛枝菌根真菌和原生动物的PLFAs含量减少。除低氮处理外,其他施氮处理样地中的土壤微生物结构都发生了改变。这些结果表明,短期氮沉降会影响杨树人工林土壤微生物群落结构,并最终可能对生态系统功能产生影响。
In poplar plantations, randomized block design was used to simulate nitrogen deposition in the field to study the effect of nitrogen deposition on soil microbial community structure. Five levels of nitrogen deposition were designed, which were blank control N0 (0 kg · hm-2 · a-1), low nitrogen N1 (50 kg · hm-2 · a-1) -2 · a-1), high nitrogen N3 (150 kg · hm-2 · a-1) and ultra-high nitrogen N4 (300 kg · hm-2 · a-1) Nitrogen treatment is performed monthly from May 2012 onwards during the growing season (May-October). Two years after nitrogen application, the microbial community structure in 0 ~ 10 cm soil layer was determined by using phospholipid fatty acid (PLFA) method. The results showed that the amount of PLFAs in bacteria and Gram-positive bacteria did not change while the amount of PLFAs in bacteria and Gram-positive bacteria increased. The content of PLFAs in fungi decreased significantly with medium nitrogen treatment, but not with other levels of nitrogen treatment. Nitrogen, high nitrogen and ultra-high nitrogen treatments reduced the PLFAs content of arbuscular mycorrhizal fungi and protozoa. In addition to the low-nitrogen treatment, the soil microbial structure in other N-treated plots changed. These results indicate that short-term nitrogen deposition can affect soil microbial community structure in poplar plantations and may eventually have an impact on ecosystem functioning.