中文摘要：

土壤微生物群落是土壤质量和生态系统功能变化的敏感指标。为了探讨放牧对土壤微生物群落结构的影响,以呼伦贝尔草甸草原肉牛控制放牧试验为平台,分析4种不同放牧强度（对照区G0.00：0.00Au/hm2、轻度放牧G0.23：0.23Au/hm2、中度放牧G0.46：0.46Au/hm2、重度放牧G0.92：0.92Au/hm2）下温性草甸草原土壤微生物群落结构的变化。结果表明,放牧改变了土壤微生物的组成,但不影响功能菌的优势地位。土壤总微生物量随着放牧强度的增加表现为先减少后增加的趋势,即为对照区最高,中度放牧G0.46最低,重度放牧G0.92出现小幅度的回升;细菌、革兰氏阴性菌、腐生真菌、丛枝菌根真菌（AMF）生物量也呈现相同变化。革兰氏阳性菌、放线菌生物量则随着放牧强度的增加而增加。此外,AMF对于放牧干扰最为敏感（各放牧强度下极显著差异P〈0.01）。除趋势对应分析结果表明,对照区G0.00和轻度放牧G0.23处理下土壤的微生物群落结构较为相似,中度放牧G0.46和重度放牧G0.92处理导致微生物群落结构发生大幅度改变。有机质、速效磷是影响微生物种类和数量的重要养分因素。

英文摘要：

Soil microbial community characteristics are an important indicator of soil quality and ecosystem functional changes.In this study,the impacts of cattle grazing intensity on soil microbial community structures were examined by phospholipid fatty acid（PLFA）in temperate meadow steppe on the Hulunber grasslands,northeastern China.Microbial communities under four grazing intensities;0,0.23,0.46 and 0.92 animal units（au）/ha with three replicates were assessed in 2013.The results showed that grazing influenced the composition of the soil microbial community.Total soil microbial biomass was highest under zero grazing,followed by the 0.92au/ha stocking rate and was lowest under the moderate stocking rate.The biomass of bacteria,Gramnegative bacteria,saprophytic fungi,and Arbuscular mycorrhizal fungi（AMF）responded similarly.There was a large,highly significantly treatment effect on AMF.The biomass of Gram-positive bacteria and Actinomyces trended upward with increased grazing intensity.In addition,we found that soil microbial community structure was similar in the un-grazed and low stocking rate treatments whereas the intermediate and high stocking rates substantial changed the microbial community structure.Soil organic matter and available phosphorus were important factors influencing soil microbial biodiversity and biomass.