The Features Of The Distribution Of Subnival Plant-Associated Bacteria And Its Relation To The Environment

Bacteria that associate with plants are diverse in the habitats they occupy, their phylogeny and their effects on plant and environmental health. Soil born bacteria adapted to competitive colonization of the spermosphere, rhizosphere and the root can be grouped under the general term rhizobacteria. An expanded definition of rhizobacteria includes bacteria from the rhizosphere, root surface (rhizoplane) and within the root (endorhizal bacteria or endophyt.es). However, very little is known about the diversity and structural composition of rhizobacteria associated with alpine subnival plants that grow in extreme environments. For this research, rhizobacteria were isolated from alpine subnival plants which grow in the freeze-thawing tundra’s at the border of glaciers. These plants are subjects to a subzero average temperature from June to September. The diversity and the features were studied through the RFLP and 16S rRNA sequence analysis of the bacteria which were isolated and cul-tured. In parallel, the correlation between the plant-associated bacteria and abiotic en-vironmental factors was analyzed. Furthermore, the bacterial population in different environments was compared. This research also discusses the diversity and transmis-sibility of bacteria associated with plants that grow in the area of stream source. The major results are as follows:1. A total of 1637 isolates were obtained from 10 different subnival plants. Phe-notypic analysis pointed out that these include 245 endorhizal bacteria,773 rhizosplane bacteria,498 rhizosphere bacteria and 121 bulk soil bacteria. The popula-tion size ranges from 0 to 109 cfu g"1. This indicated that plants growing under ex-treme environmental conditions contain a variety of plant-associated bacteria and show a regular distribution characteristics along with micro-environment, compared to plants that grow in normal habitats.2. Based on the RFLP analysis and 16S rRNA gene sequences, a total of 93 bac-terial genera that vested in Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria were found in subnival plants. Thereof Proteobacteria formed the larg-est cluster and possessed the highest taxonomic diversity, for which were observed in each plant species and included above 45 genera. The other three, Actinobacteria, Bacteroidetes and Firmicutes, compared with Proteobacteria, were in the second, third and fourth places.3. From the aspect of micro-environment, the distribution of the bacteria fluctu-ated in number and species. Specifically speaking, bulk soil bacteria were observed to obtain the most Proteobacteria, whereas the number and species of the Bacteroidetes and Firmicutes were compared to be less. The abundance ratio of rhizosphere bacteria was higher than bulk soil bacteria and lower than rhizoplane bacteria. When men-tioned about rhizosphere bacteria, the abundance ratio ranked in the third place.4. The distribution feature of population structure and physiological characteris-tics of plant-associated bacteria, isolated from subnival plants, varied as the altitude. To be more specific, the abundance ratio of the bacteria lowered along with the alti-tude decreasing. The number and the species were positively correlated to C/N ratio, and Proteobacteria showed significantly positive correlation to C/N ratio.5. During blasting the sequences, we found several plant-associated bacteria, which Flavobacterium sp. Dcb6, Flavobacterium sp. Ezall, Janthinobacterium sp. Abb5, Devosia sp. Bma11、Devosia sp. Emb15 and Flavobacterium sp. Eza24 have low similarity to other rRNA sequences. Due to these facts, we suppose that these strains may belong to new species.6. Plant-associated bacteria, isolated from subnival plants in Tianshan, are simi-lar to those isolate in other cold environments and associated with the plants which growing in similar temperate environments. Moreover, G+ bacteria possessed the high diversity in cold environments, whereas G- bacteria accounted for most proportion in tropic or temperate plants. This was in line with the idea that the occurrence of related phenotypes and genetic diversity in geographically diverse cold environments was possibly due to similar strategies to survive freezing and remain active at low temper-ature.