Study Of Microbial Diversity In Nitrogen Fixing Plant Hippophae Rhamnoides Rhizosphere In The Loess Plateau Of Shaanxi Provice

In order to explore the role of non-leguminous nitrogen fixing plant Hippophae rhamnoides'growth-promoting rhizobacteria in promoting vegetation restoration and ecosystem reconstruction in Loess Plateau, the soil and root nodule in Hippophae rhamnoides rhizosphere in Shaanxi province was used to detect the relationship between microbial population structure and soil fertility and to study the diversity of hydrogen-oxidizing bacteria, Frankia and Vesicular-Avbuscular mycorrhiza fungi. According to the analysis of the result of above experiments, we can realize the generic distribution of hydrogen-oxidizing bacteria, enrich the existing research about sort of hydrogen-oxidizing bacteria and explore the relationship and mechanism of polymicrobic growth-promoting in Hippophae rhamnoides rhizosphere. The main experimental content and results were as follows:We used gas cycle incubation system to treated rhizosphere soils with H2 produced by water electrolysis. The result showed that the microbial population structure of the soil treated with H2 had changed:the number of bacteria and actinomyces had increased,and the number of hydrogen-oxidizing bacteria had increased significantly, but the number of fungi had declined. The microbes'respiration intensity and activity of soil enzyme in soil treated by H2 had enhanced to varying degrees; organic matter content of soil and planthormones in soil had grown in number, which explained that the soil fertility had enhanced with the treatment of H2.Fifty nine bacterial strains were isolated by gas-cycle incubation system and MSA medium. Twelve strains among them which contained hydrogenase and had strong ability to oxidize hydrogen was selected by TTC test, gas chromatograph and autotrophic gowth detection, suggesting that they might be hydrogen-oxidizing bacteria initially. Hydrogen-oxidizing ability of strain FS2 was about 35.430μmol/L.Based on their morphological, cultural,and physiological and biochemical characteristics, these 12 strains were identified as members of genera Bacillus, Aeromonas, Pseudomonas, Micrococcus, Xanthomonas, Brachybacterium, Nocardia and Pimelobacter,respectively. The 16S rRNA gene sequence analysis suggested that strain FS2 (GenBank accession number GU084156) was clustered together with Bacillus in phylogenetic tree, with sequence similarity more than 99%.We used thin layer chromatography to find out that strain FS2 and WS4 could consum-ed ACC and contained ACC deaminase.Then we detectd the influence factors about the activity of the ACC deaminase. The result showed that the two strains could decompose nearly 90% ACC in 24h and the optimal temperature was 30-35℃and the optimal pH was7.0-7.5.Three endophyte strains SY1, SY2 and SY3 were isolated from root nodule of Hippophae rhamnoides,.They belonged to slow-growing actinomyces and formed flocculent or granular precipitate in the BAP liquid medium; their hyphae was filamentous with different diameters under microscope and could produce vesicle when growing in the nitrogen-free medium. Above characteristics was in line with general characteristics of Frankia, therefore the 3 strains could be identified as a member of Frankia preliminarily. The study of 3 Endophyte's biological property showed that strain SY1 and SY2 were divided into physiological group A and strain SY3 was divided into physiological group AB.Their optimal carbon sources were tween-80 and glucose, and optimal nitrogen sources were ammonium sulfate and nitre.Acid fuchsin was used to dye root segment of Hippophae rhamnoides and the result showed that the Hippophae rhamnoides root system was infected by Vesicular-Avbuscular mycorrhiza fungi and the infecting rate were 55.6%,72% and 65%, respectively. SevenVA fungi species belonging to 2 genus were isolated and identified by sieving and deeanting proeedure from Hippophae rhamnoides rhizosphere soil.Six species were belonged to genus Glomus, including Glomus claroideum, Glomus consrictum, Glomus intraradices, Glomus geosporum, Glomus diaphanum and Glomus reticulatum,and Gigaspora gigantean was belonged to genus Gigaspora.