Phylogenetic And Functional Diversity Of Bacterial Community In Tibet Plateau Permafrost Soils

Permfrost stored large quantities of organic carbon, while their degradation were conducted by soil microbial communities. Due to the global warming, thawing of near-surface permafrost will widespread and the trapped organic matter may become more accessible for microbial degradation, resulted in greenhouse gas emissions. It reported that the reverse succession of alpine ecosystem in Qinghai Tibet Plateau(QTP) has been enforced as the consequences of permafrost degradation. Accompanied the shifts of topography and hydrological condition of permafrost in QTP, such as permfrost temperature increasing, soil moisture and nutrient losing, a retrograde seccession from alpine swamp meadow(SM), alpine meadow(AM) and alpine grassland(AG) to alpine desert(AD) has been observed in alpine landscape. However, no comprehensive study has yet addressed on microbial commuities responsing to this series vegetation change gradient in QTP.In this study, permafrost-affacted soil samples were collected from four kinds of vegetation type in alpine ecosystem of QTP. Cultivation-dependent and cultivation-independent methods, such as pyrosequencing and Biolog EcoPlateTM, were used to reveal the microbial communities abundance, composition and potential function in alpine ecosystem of QTP. The results obtained here were summarized as follow:1. Soil characteristics and microbial abundance: Along the vegetation succession, from SM to AD, accompanied soil moisture and nutrient decreasing, soil pH and C/N increasing, culturable microbial CFUs and total cell numbers were all shrinked from2.88x107CFU/g to2.97x106CFU/g, and1.14x109cells/g to4.36x108cells/g, respectively.2. Phylogenetic diversity of microbiota in permafrost-affacted soils:Phylogenetic analysis results showed that the dominant phyla in all samples were Actinobacteria, Acidobacteria, Proteobacteria, Bacterioidetes, Firmicntes, Chloroflexi, Nitrospirae, Gemmatimonadetes and Candidate_division_TM7, while the δ-proteobacteria, Acidobacteria, Chloroflexi, Nitrospirae, Gemmatimonadetes and Candidate_division_TM7were not isolated by culturable-dependent method. The composition of bacterial community was changed with the vegetation degradation in alpine ecosystem of QTP. For example, certain kinds of strains abundance linearly rised or declined from SM to AM, implying that we can use these strain number information as the indicator of nutrient state for permfrost-affacted soil in alpine ecosystem of QTP and that it provide the cules for the prediction of microbial community shifts as environment changing.3. Functional features of microbiota in permafrost-affacted soils:Using Biolog EcoPlateTM approach to study microbial community level function, the results demonstrated that accompanied vegetation types changed from SM to AM, AWCD gradually decreased and Polymers become the main carbon source decomposed by microbes instead of Amino Acids. So it needed to deeply investigate the impact to climate change as carbon source profile shifting.4. Factors governing the microbial communities: Correlation analysis showed that soil moisture and nutrient level were significantly correlated with microbial commuinies abundance in most case.While soil pH and C/N were significantly correlated with microbial phylogenetic and functional diversity indexes. It suggested that soil moisture and nutrient content shipped the structure of microbial communities at some extent and soil pH, C/N controlled the microbial diversity as usual. In addation, principle component analysis showed different distribution patterns of four vegetation succession stages due to the OTUs from pyrosequences, indicating that plants cover aboveground and soil properties were major biotic and abiotic factors influenced the microbial communities underground.The data obtained in this study demonstrated that accompanying by the dynamic changes of vegetation types in permafrost-affacted soil regions of QTP, bacterial abundance, phylogenetic diversity and functional features were fluctuated accordingly as well, even improved our understanding the relationship among soil parameters, microbes and vegetations.