Research On Change Of Soil Microorganism In Different Degenerate Desert Steppe Of Inner Mongolia

The grassland ecosystems are the largest terrestrial ecosystem in China, which play an important role in maintaining the pattern, function and process of natural ecosystem. Desert steppe of Inner Mongolia is the primary natural community in northen China, and there are different levels of degradation. Soil microorganisms play a major role to soil ecosystem, however littele information is available about soil microorganisms of degenerated ecosystem. In this paper, the change of the soil microbial community structure was studied by traditional methods and modern molecular biology methods in different degenerated desert steppe of Inner Mongolia. The results show below:1. The relationship among the quantities of the various soil microbial of desert steppe ecosystem is Bacteria > Actinomyceto > Azotobacteria > Fungi. With the expansion of degradation degree, the quantities of microbe were decreased in some tendency: lightly degenerated area is the highest, and the lowest is the heavily degenerated area, and ratio of major groups is correspondingly stable in different degenerated phases.2. Soil organic matter content was the highest in lightly degenerated areas, and it decreased with degeneration of desert steppe ecosystem from light to heavy degenerate phases. The similar pattern was detected in soil total nitrogen content while orderliness of soil total phosphorous, soil total potassium and PH value are not obvious at different gradient levels.3. The results of soil bioactivity indicated: degeneration of steppe had an apparent effect on soil microbial biomass C and respiration intensity, which were reducing along with degeneration of desert steppe ecosystem from lightly degenerated to heavily degenerated stages. Similar trend was detected in soil Urease, soil Invertase, Peroxidase and Polyphynoloxidase activity and soil enzyme activities were changed markedly in different samples, and it showed relatively high fertility levels and characteristics of fast turnover rate in lightly degenerated areas.4. Correlation analysis on the factors of the soil indicates that the soil microorganisms,soil nutrition and soil activity in desert steppe ecosystem were depended and affected together. Particularly, there was significant correlation between soil properties and soil biological activity. Therefore, the combination of soil properties and soil biological activity was the effective indicator to evaluate the soil health and fertility.5. Soil microbial total DNA was extracted from different degenerated samples and PCR amplification was processed. DGGE was used to study 16S rRNA (V6-V8 region) of soil microbial community, the result shows that the high G + C mol% microbes were the dominant groups in study area and the structure of soil microbial community changed a lot while the degeneration of desert steppe was processing, and it shows the degeneration of steppe changed the structure of soil microbial community markedly.6. Index of soil microbial diversity was also studied in different degenerate area. The results show that the Shannon-Weaver index and Simpson index were decreased when the degeneration of desert steppe was progressing. So bacterial community diversity was changed significantly by degeneration of the grassland.7. The phylogenetic affiliation of soil microbe in different degenerated steppe was determined by 16S rDNA sequencing of cloned DNA fragments: the sequences of the clone in different degenerated desert steppe ecosystem were mainly attributed to Bacteroidetes, Acidobacteria, Proteobacteria and itsγ,δgroups and Firmicutes. Bacteroidetes is the dominant species of the three soil samples, at the ratio of about 47%.8. Degeneration of grassland lead to decrease of plant diversity based on conventional investigation of study area. The result of research between vegetation and soil microbial diversity in study area shows that there is close relationship between ground vegetation and microbial diversity, result of correlations present that there is a positive correlation between plant diversity and microbial diversity.