| Desertification is a global ecological environment problem in the world today, much more attention has being paid on to it. Plant growth promoting bacteria (PGPB) such as nitrogen fixing bacteria and phosphate solubilizing bacteria can provide nitrogen, phosphorus and other nutrients for plants, improve the fertility of the soil, promote plant growth, increase the stress resistance of plants and enhance the quality of the soil, showing the valualbe significance in the soil desertification prevention and control.Large areas of the desert steppe is existed in Inner Mongolia, where PGPB may fulfil a major and positive role in the contolling the desertification. As is the basis of the exploration and application, however, the study on PGPB diversity is still in deficency.This study uses pure culture and molecular biology DGGE technology study the diversity of PGPB related with primary plant dominant species in desert steppe of Siziwang Banner. The results showed that:(1) Three types of midia (beef extract peptone medium, Ashby medium and inorganic phosphorus medium) were employed, and176bacteria strains were isolated, including37strains of rhizosphere bacteria,38strains of endophytic bacteria,21strains of rhizosphere diazotrophic bacteria,27strains of endophytic diazotrophic bacteria, phosphate solubilizing bacteria37strains,16strains of endophytic phosphate solubilizing bacteria. These strains belonged to Bacillus, Brevundimonas, Arthrobacter, Streptomyces are the dominant groups. Among the isolated strains GN0603and RN0603had higher nitrogenase activity with88.25and73.95nmolh-lmL-1respectively. Strains GP0801, GP0802, GP0803and RP0802showed higher ability in dissolving phosphorus, reaching at66.824,53.518,60.632and64.021μg/mL respectively. These strains may have paticular value for development and application.(2) At summer, Siziwangqi desert steppe is under the most severe environmental conditions, but rhizosphere and endophytic bacteria, nitrogen fixing bacteria of five kinds of main dominant species showed large diversity. Through the16S-DGGE analysis, the16S rRNA sequences of rhizobacteria and endophytic bacteria were derived from five plants belong to Actinobacteria, Cyanobacteria, Bacilli, a-proteobacteria, β-proteobacteria, Gammaproteobacteria and Allium sativum chloroplast. Sequences of two dominant groups were closyly affiliated to Uncultured bacterium clone K1-434 and Allium sativum respectively. Analysis of nifH-DGGE revealed that the obtained nifH sequences of rhizobacteria and endophytic bacteria affiliated to those of Bradyrhizobium, Zoogloea, Burkholderia, Azohydromonas, Mesorhizobium, Ideonella, Azospira and some uncultured nitrogen fixing strains. Sequences of the most dominant groups mostly affiliated to nitrogenase iron protein [uncultured bacterium](AEB96802). There are no significant differences in rhizosphere bacterial community structure and abundance between plant species, while the nitrogen-fixing bacteria of rhizosphere and endophytic diazotrophic bacteria has been observed markedly differences on the community structure and abundance.Using pure culture method, we have got many species of nitrogen fixing bacteria and phosphate solubilizing bacteria. Some strains showed strong growth promoting ability. DGGE analysis showed that rhizosphere and endophytic bacteria, nitrogen fixing bacteria all have abundant diversity. The most dominant bacteria affiliated to uncultured bacteria. Suggest that the Siziwangqi desert grassland is rich in plant growth promoting microbial resources. This study can promote the understanding of growth promoting bacteria diversity of plants in the desert steppe of Siziwangqi. This study provide theoretical basis and technical support for the development and utilization of functional microbes of desert grassland, biodiversity conservation and ecological restoration of desertified soil. |
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