Microbial Diversity In Tianshuihai Permafrost Soil, Tibetan Plateau

Qinghai-Tibet Plateau, the world’s highest and youngest plateau, contains vast area of permafrost. In recent years, with global warming, permafrost degradation intensifies, the active layer deepened, the process of microbial metabolism becomes more active, and large amount of carbon stored in permafrost will be released into the atmosphere as the metabolites of microorganisms CO2and CH4, which will intensify the process of global warming. However, little is known about changes in microbial community in the active layer, and whether the microbial community will be different between the active layer and the permafrost as the climate becomes warmer.In this study, we investigated a53m sediment core drilled from Tianshuihai basin, Tibetan Plateau. Fluorescence microscopy counting and high-throughput pyrosequencing technology were used to reveal the bacterial, fungal and archaeal community structure and distribution in different depth of sediment. The results obtained were summarized as follows:1. Soil properties and microbial abundance:The soil of permafrost sediments in different depths was alkaline, and the carbon and nitrogen content was very low. Soil depth was significantly correlated with total P, soil organic C and soil moisture (P<0.01). While soil organic C was significantly correlated with total P. The total number of microorganisms in permafrost was2.97×108-2.45×109g-1soil, which was significantly correlated with soil depth.2. Phylogenetic diversity of bacterial community:A total of12430bacterial OTUs with85828reads were identified from19different depths, which could be assigned into23different phyla, and383genera. The dominant bacteria categories included:Proteobacteria、Actinobacteria、 Firmicutes、Bacteroidetes、Gemmatimonadetes、Cyanobacteria、Acidobacteria、Chloroflexi、 Candidate_division_TM7and Nitrospirae. The bacterial community composition and structure was different between active layer and permafrost, for instance the Bacteroidetes was less abundant in permafrost in comparison with the active layer and, in contrast, some other groups were more abundant (for example, the Firmicutes) in the permafrost.3. Phylogenetic diversity of fungal community:A total of11356fungal OTUs with108,091reads were identified from18different depths, which could be classified into10different phyla, and329genera. The dominant groups was:Basidiomycota、Ascomycota、Fungi incertae sedis、 environmental samples、Glomeromycota and Chytridiomycota. Correlation analysis showed that the the fungal OTUs, community richness index (ACE, Chaol) and Shannon diversity index significantly correlated with soil depth and TP. Fungal community was different in the active layer from that in permafrost, both abundance and diversity of fungal communities were higher in permafrost compared with the active layer.4. Phylogenetic diversity of archaeal community:A total of50657archaeal reads, with the average of3618reads per sample, were identified from14different depths, which related two major archaeal phyla, Euryarchaeota and Crenarchaeota. Our study showed that Crenarchaeota abundance was more abundant than Euryarchaeota. The majority sequences related to Euryarchaeota was Halobacteria, indicating that the permafrost in Tianshuihai basin may originate from the ocean. Archaeal community structure was different in the active layer and permafrost, the relative abundance of Euryarchaeota was higher in active layer, on the contrary, the relative abundance of Crenarchaeota was higher in permafrost.The results obtained in this study demonstrated that there were great differences in soil physicochemical properties, microbial abundance, microbial diversity and community composition between active layer and permafrost. The long-term exposure to low temperature, low water and nutrient availability probably reduced microbial diversity and abundance in the permafrost, also causing some shifts in the community composition. The larger environmental fluctuations occurring in the active layer soil as compared with the permafrost might also have caused some of the differences observed in community composition.