Effects Of Forest Degradation On Soil Microbial Microbial Diversity In Southern Slope Of Daxing’an Mountains

The degradation of vegetation is a widespread problem in Northern Forest ecosystems, it restricts the ecosystems’function of holding water and conserving the land. Simultaneously, biological diversity of local ecosystems is on the hazard. Changing to grassland is the main indicator of forest degradation in Daxing’an Mountains, research on succession of microbial functional and structural changes is of great significance to explore the driving mechanism of forest degradation. Therefore, this paper studied the changes on soil nutrients, enzyme activity, soil microbial community structure and functional diversity in degrading process (Quercus Mongolica forest, shrub bush and grassland). The results are as follows:The amount of soil nutrient show that:the shrub bush and grassland exhibit a high degree of similarity in aspects of soil moisture content, pH, organic carbon, nitrogen, phosphorus, potassium. Along with increasing degradation, soil organic carbon, nitrogen, phosphorus, potassium content decreased, soil fertility also reduced. Vegetation degradation has different affects on soil Enzyme, the activity of urease, invertase and phosphatase peformed as Quercus Mongolica forest> shrub bush> grassland. Along with increasing degradation, urease, invertase and phosphatase activity decreased, the soil catalase activity did not change with soil depth and degree of degradation.There are significant differences between three types of degenerated soil microbial in the ability of using carbon sources, which, the average well color development(AWCD) fluctuated between 0.25 to 0.39,the order is:shrub bush>Quercus Mongolica forest>grassland, the values between shrub bush and grassland reached significant differences level, Shannon index (H), and carbon source utilization richness index(S) presented similar tendency. Differences in carbon utilization exist between three types of vegetation, amino acids utilization is Quercus Mongolica forest> shrub bush> grassland, in contrast with the use of amines/amides, showing that forest changing to grassland in Daxing’an Mountains lower the diversity of rhizosphere soil microbial communities, suppress the quantity and activity of soil microbial which could use carbon sources, decrease the capability of microbial using single carbon substrates.In this study,454 pyrosequencing was applied to investigate the diversity of rhizosphere soil samples from 3 kind of vegetations in order to explore the soil bacterial community structure and reveal the effects of different restoring measures on rhizosphere soil microbial diversity. The results indicated that a total of 948 operational taxonomic units(OTUs) were obtained from three groups of rhizosphere soil, while 455 OTUs were shared by three group of samples.12 bacterial phylums in three soil samples were distributed, the order of taxa percentage at phylum level were as follow:Proteobacteria> Acidobacteria> Plantomycetes> Firmicutes> Bacteroidetes> Nitrospirae> Chloroflexi> Gemmatimonadetes> Verrucomicrobia> Elusimicrobia> Chlorobi> Armatimonadetes, which the Proteobacteria and Acidobacteria were the dominant flora. Forest degradation changed the distribution of main soil microorganism groups in the rhizosphere, there are significant differences on genus Bacillus, Microvirga, Gaiella, Acinetobacter, Granulicella, Rhizomicrobium, Bryobacter and Burkholderia. The indices of Chaol and Shannon showed that the abundance and diversity of soil microbial community ranked as follow:Quercus Mongolica forest>shrub bush>grassland. The results demonstrate forest degradation changed the abundance distribution of each cluster in community and decreased some special flora with decreasing the functional diversity of carbon metabolism, increasing degradation would reduce diversity of soil microbial community.