中文摘要：

微生物群落组成变化是研究和预测陆地生态系统对全球变化响应的重要工具。通过监测模拟气候变化的施氮增雨试验条件下土壤微生物群落的改变，预测我国北方半干旱草地生态系统在未来对全球变化的响应。为了更好地衡量微生物群落的响应，进行了连续3年的气候模拟试验，利用磷脂脂肪酸（PLFA）图谱分析法追踪微生物群落结构变化。结果显示，增雨对微生物群落中的革兰氏阳性菌（GP）、革兰氏阴性菌（GN）以及总细菌和总真菌的PLFA含量没有显著影响，但对真菌／细菌比（F／B）和革兰氏阴性菌／阳性菌之比（GN／GP）有显著影响，并显著降低了总PLFA含量。施氮显著降低了微生物群落中的革兰氏阳性菌、革兰氏阴性菌以及总细菌和总真菌的PLFA含量，并显著降低了微生物群落的总PLFA含量。施氮和增雨两个环境变化因子对总PLFA、GN／GP、以及真菌对细菌之比（F／B）有显著的交互影响。在半干旱草原地区，施氮和增雨对微生物群落结构存在交互影响。这预示着未来降雨量增加和氮沉降条件下，我国北方草地生态系统中，微生物群落结构变化将导致微生物群落生态功能改变，从而引发整个生态系统的响应。

英文摘要：

In order to make contributes to further prediction of the reactions of terrestrial ecosystem to global change, we conducted a 3-year field experiment simulating increasing precipitation and N deposition in the coming decade in the semi-arid grassland ecosystem of Northern, China. Phospholipid fatty acid analysis （PLFA） was used to investigate the changes of soil microbial composition. The results showed that increased precipitation had no significant impact on microbial groups of Gram Positive bacteria （GP）, Gram Negative bacteria （GN）, total bacteria and fungi; but decreased the total PLFA and changed the ratios of fungi to bacteria （F/B） and GP/GN significantly. N addition had increased PLFAs of microbial groups such as GN, GP, bacteria and fungi, thus reduced the total PLFA. Increased precipitation and N addition had interactive effects on total PLFA and the ratios of F/B and GN/GP. According to the research, increased precipitation and N addition had interactive effects on microbial compositions in semi-arid grassland. The significant correlations between microbial communities, soil and plants needed further investigations in future research on the reactions of semi-arid ecosystem to global change.＂