Investigation Of Oligotrophic Bacteria And Its Ecological Effect From The Desert Soil In The Eastern Side Of Ningxia Helan Mountain

Oligotrophic microbe widely exists in some extreme environment, has a unique ecological significance. There are some oligotrophic bacteria exist in desertified soil, some research have shown that they secrete some adhesive substance such as extracellular exopolysaccharides in the process of development, it can stabilize soil surface, help sand-fixation effectively, affect the physical and chemical properties of the soil, so that promote the formation of soil microorganism crust.In this topic, we collected soil samples of different types of environment from the eastern side of Ningxia Helan mountain, and studied physico-chemical characteristics and microbial diversity about this three typical environment type, separate oligotrophic microbes from the soil, and the ecological effect of typical oligotrophic in desert soil are studied. thesis research results are as follows:(1) The structure and diversity of bacteria from three typical soil samples were detected by the way of PCR-DGGE. The results showed that there is difference in the DGGE map of 16S rDNA V3 fragment among three samples, the clone sequence blast of the DGGE bands demonstrated that the soil bacteria in the eastern side of Ningxia Helan mountain could mainly be classified as Actinobacteria, Deltaproteobacteria and some unnamed strains, and most of them were uncultured. Combined with the lab research about investigation of microbial communities structure in biological soil crusts of desert, the results show:two kinds of bacteria which exists in the specific band sequencing of DGGE are Deltaproteobacteria and Micromonosporaceae bacterium, also exists in the early stage of microbial crust development, but to the late stage (3-5) their numbers began to reduce, speculated that these two kinds of bacteria could promote the formation of microbial crust development.(2) The results of correlation analysis demonstrated that bacteria diversity, soil organic matter, water content biomass and bacteria diversity were significantly related with each other, is an important factor affecting the amount and species of microorganisms in the oligotrophic environment.(3) Separate and identify five strains of oligotrophic bacteria from the soil with poor nutritional conditions, respectively named P1、P2、P3、 P4 and P5, combined with morphology observation and sequencing analysis of 16S rDNA sequences results, P1、P2、P3 and P5 are Streptomyces, P4 bacterium is bacillus subtilis, temporarily named strain P4. it optimum growth temperature is 37℃, optimum pH value are between 7～8, the optimum carbon content is 15 mg/L.(4) Oligotrophic microbe ecological effect of soil desertification on the test results showed:after spraying microbial agents of strain P4, water content, and water-holding have significantly improved, water permeability has dropped significantly. And strain P4 has a strong phosphate-solubilizing and K-release ability. these two characteristics is essential for poor soil increases its fertility, provide nutrition matrix for microbial growth and development, and promote microbial soil crust.