Studies On Microbial Community Strecture And Spatial Heterogeneity In Wuliangsuhai Wetland

Soil microorganisms are sensitive to changes in environment and play critical roles in the responses of ecosystems to natural or anthropogenic perturbations. Therefore, it is necessary to understand the functions of microbial communities in different environments and the influence of their structural and functional changes in the ecosystems. The Wuliangsuhai wetland in western China is the largest natural wetland along the same latitude on the earth. In recent years, the growth of industrial and agricultural practices, together with the continuous growth of population and urban development, have caused a significant degradation of Wuliangsuhai wetland. Excess nutrients input and accumulation of phosphorus (P) and nitrogen (N) resulted in lake eutrophication and produced harmful algal blooms and destroy wetland integrity and function, which is a direct threat to the ecological safety of the Hetao Plain in China.In this study, we reported a survey of the microbial population of Wuliangsuhai wetland. We established plots throughout the south shore of the Wuliangsuhai Lake from the lakeshore to the land:(1) Phragmites australis community/(2) Kalidium foliatum community/(3) Suaeda salsa community/(4) Nitraria tangutorum community. We also collected the surface sediment.The soils’ physicochemical properties vary at different sample sites, indicated by the water content, pH, organic carbon, total nitrogen and total phosphorus. To investigate the community structure of soil microbes in the Wuliangsuhai wetland, the composition and distribution of bacteria, fungi and actinomycetes were studied. The bacterial community structures, distribution and dynamics, especially the diversity and richness of dominant bacteria diversity of each site were analyzed by a barcoded pyrosequencing. The responses of these dominant microbes to the environment were also discussed, in order to find fundamental reasons that cause higher spatial heterogeneity of bacteria community, and the mechanism that integrates microorganisms with its environment due to the different type of soils. This research provided new insights into and added valuable reference for the bacterial communities in Wuliangsuhai Wetland ecosystem with the obtained data on the distribution, diversity and functions of bacteria in wetlands, and the relationships they share with their environment identified and discussed in this thesis.The analysis of the physicochemical properties of the soil revealed that in the Wuliangsuhai wetland, the sample sites have a narrow range of alkaline pH values. The sites varied widely in water content. The soil water contents were reduced gradually along the study transect. Compare to other wetlands, the Wuliangsuhai wetland has a lower nutrient content in the soil. All the sediment samples have alkaline pHs and high water contents. Organic carbon content of sediment was 14 times higher than that in the wetland soil. The ratio between carbon and nitrogen in sediment was much higher than that in wetland soil. No significant differences in the total phosphorus content between sediment and wetland soil.The composition and distribution of bacteria, fungi and actinomycetes were also investigated in this thesis. Results indicated that the quantities of microorganism vary in wetland soils with different vegetation. In all the samples, bacteria were dominant, while fungi were the lowest among all the microorganisms. The largest number of bacteria, fungi and actinomycetes found at Nitraria tangutorum soil, and the Kalidium foliatum soil had the fewest microorganisms. For sediment samples, the largest number of bacteria in sediment was found at BW2 and XHK sites, fungi and actinomycetes were the most abundant at HGB and TS sites respectively, while TS and BW1 had the highest spore-forming bacteria.The bacterial communities of Wuliangsuhai wetland were evaluated using 16S rRNA gene multiplex 454 pyrosequencing. Library coverage values and rarefaction curves indicated that these libraries were representative for the majority of bacterial 16S rRNA gene sequences in each sample.The most abundant bacterial groups in all four soils were the Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadetes and Acidobacteria. Taxonomic classification of pyrosequencing reads showed variable bacterial diversity among different vegetation soil sites. The relative abundance of Actinobacteria was increased from 1.85% to 16.39% along the study transect, whereas that of Bacteroidetes was decreased from 11.39% to 6.45%. The Deltaproteobacteria were the dominant classes in the Phragmites australis soil and Kalidium foliatum soil, while Epsilonproteobacteria, Gammaproteobacteria were the dominant classes in the Suaeda salsa soil and Nitraria tangutorum soil, respectively. The overall bacterial communities shared significant correlations with site water content, total phosphorus and total nitrogen concentrations.Sequencing results showed that the dominant taxonomic groups across all sediment samples were Proteobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Acidobacteria and Planctomycetes. Compared with the wetland soil, Actinobacteria and Gemmatimonadetes were no longer the dominant group, and the special sediment environment made Planctomycetes becoming the dominant group. The relative abundances of bacterial groups at different taxonomic levels correlated with total phosphorus (TP) and total nitrogen (TN) concentrations.