| Grazing was the main way for natural grassland utilization, and exclosure had been widely adopted all over the world as a major measure of pasture recovery and reconstruction. In this paper, 3 different Stipa types (Stipa baicalensis meadow steppe, Stipa grandis typical steppe, and Stipa krylovii typical steppe) in Hulunbeier were the research objects, the responses of soil physico-chemical properties, soil microbial diversity and soil enzyme activity to grazing and fenced were researched by field survey and laboratory analysis, theory and methods of modern ecology, and modern biotechnology PCR-DGGE and PLFA. The main conclusions were as follows:1. There were significant differences in soil physico-chemical properties between inside and outside fence plots. Under the grazing pressure, the pH value of soil increased significantly, the content of soil water and soil organic matter content decreased significantly, soil total nitrogen content and total phosphorus content were also decreased remarkably in S. grandis and S. krylovii. Among the three Stipa steppes, the activities of soil alkaline phosphatase and invertase tended to increase at grazed grassland compared with fenced grassland, while, the changes of soil urease and catalase activities varied with different grassland types. There was a significant correlation between soil enzyme activities and main soil fertility factors (organic matter content, total nitrogen, available phosphorus).2. The analysis of Chloroform-fumigation extraction showed that there were significant differences in soil microbial biomass between grazed and fenced steppes. Soil microbial biomass carbon, nitrogen content ranged from 166.6 to 703.5mg·kg-1, 30.34 to 92.15 mg·kg-1 respectively, while the microbial biomass at Stipa baicalensis meadow steppe was largest, followed by Stipa grandis typical steppe, and the lowest was at Stipa krylovii typical steppe. The microbial biomass at the fenced plots in Stipa baicalensis meadow steppe and Stipa grandis typical steppe was significantly lower than that at the grazed plots, and no difference was found in Stipa krylovii typical steppe.3. The results of PLFAs displayed that Stipa steppes in Hulunbeier showed abundant species and quantities in soil microbial communities. The bacteria PLFAs and total PLFAs in the fenced plots were much higher than those at the grazed plots. The changes of fungi PLFAs varied with different grassland types. Grazing decreased significantly the ratio of gram-positive bacteria PLFAs/gram-negative bacterium PLFAs (GP PLFAs /GN PLFAs) and remarkably increased the ratio of bacterial PLFAs/fungi PLFAs except at Stipa krylovii typical steppe. Principal component analysis (PCA) indicated that soil microbial community structure was influenced by different regimes of grassland utilization, grazing > exclosure. Correlation analysis of soil PLFAs content and soil nutrients indicated that soil microbial PLFAs significantly correlated with soil organic matter, total phospholipids and ammonium nitrogen.4. There were abundant microbial diversity and seven major clusters: Proteobacteria (39.4%), Bacteroidetes (24.2%), Actinobactetia (15.2%), Acidobacteria (15.1%), and a little of Gemmatimonadetes, Firmicutes, Fusobacteria, and most of them were uncultured microorganisms, among which, Proteobacteria and Bacteroidetes were the dominant groups in Stipa steppes. The sequences of Proteobacteria consisted ofα,β,δandεfour types, the proportion being 18.2%, 12.1%, 6.1% and 3.0%, respectively. Higher similarity and more stable community structure existed among soil bacterial communities in different types of steppes at grazed and fenced grassland, while, the bacterial diversity, Shannon-wiener index, Shannon evenness showed significant differences between grazed and fenced grassland.
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