Diversity And Community Structure Of Rhizospheric Bacteria Associated With Desert Shrubs In The Western Ordos

Desertification is a global ecological and environmental problem, especially in our country. Desert shrubs have strong capability in drought resisting and poor nutrition enduring, and thus they play a crucial role in the balance and restoration of desert ecosystems. Some bacteria, mainly including nitrogen-fixing and phosphorus-dissolving bacteria, promote plant growth, through improving soil fertility, plant stress resistance and increasing plant productivity, and may have important theoretical significance and practical value in the respects of stabilizing desert ecosystem and.Western ordos is located in the arid and semi-arid desertand its shrubs’ rhizosphere bacterial diversity and community structure is unknown so far. This research applied the high-throughput sequencing technology and pure culture method to reveal the diversity and community structure of Helianthemum songaricum, Sarcozygium xanthoxylon, Nitraria tangutorum, Ammopiptanthus mongolicus and Tetraena mongolica, in the regions of the Qianlishan mountain and Balagong of the western ordos. The main results and conclusion are as follows:1. Soil physical and chemical properties:there were no obvious differences observed on soil pH, water content, available N and available P between Balagong and Qianlishan mountain. However, the rhizospheric organic matter contents in Qianlishan mountain was much higher than those of Balagong. The available phosphorus, available nitrogen and organic matter of the rhizosphere soil of Tetraena mongolica were the highest, respectively 5.60/3.57 mg/kg(Qianli/Balagong),122.50/77.00 mg/kg and 13.41/2.65 g/kg。2. Microbial diversity indexes:the copy number of rhizosphere soil bacteria, microbial diversity of Qianlishan mountain were higher than those in Balagong. Bacterial abudance of Helianthemum songaricum and Ammopiptanthus mongolicus was the maximum and the minimum with the 16 s rRNA gene copy number of 1.38* 108 and 5.2* 105/g soil respectively. The bacteria diversity index of the Helianthemum songaricum is the highest (Shannon, ACE and Chao value of 7.89,28571 and 17489 respectively) and lowest sequencing coverage (76%).3. Community structure:Qianlishan mountain shrubs’ bacterial OTU number was in the range of 6130-6130, mainly divided into 29 phylum and the top ten were Proteobacteria (35.93% 43.01%), Actinobacteria (22.24% 22.72%), the Bacteroidetes (9.18% 13.21%), Acidobacteria (4.72% 5.92%), Gemmatimonadetes (4.95% 5.75%), Planctomycetes (0.61% 2.24%), Verrucomicrobia (1.33% 1.96%), Firmicutes (1.58% 1.63%), TM 7 (0.84% 1.35%) and Chloroflexi (0.56% 0.57%).The number of OTU in Balagong shrubs ranged from 3641 to 5322, mainly divided into 31 phylum with the dominant Proteobacteria (39.6% 49.33%), Fusobacteria (4.29% 17.44%), Firmicutes (9.72% 12.11%), the Bacteroidetes (8.47% 11.83%), Actinobacteria (2.64% 4.18%), Acidobacteria (3.28% 5.96%), Chlorobi (1.46% 3.08%), Chloroflexi (1.43% 3.55%), Gemmatimonadetes (0.58% 1.04%), Verrucomicrobia (0.75% 1.45%). The difference of Bacterial community between the two regions was obvious.4. Soil properties effect on community:among six environmental factors, soil organic, water content, and pH had more effect on the composition of microbial communities while available N and phosphorus had less effect.5. Nitrogen-fixing and phosphorus-dissolving bacteria:total 127 bacterial were isolated and purified from Balagong and Qianlishan mountain shrubs’rhizosphere,53 nitrogen fixing and 74 phosphorus-dissolving strains, of which, Including the azotobacter and soluble phosphorus of rhizosphere or endogenous strains 40 and 13,62 and 12 respectively. The rhizosphere azotobacter has 14 species, and the endophytic azotobacter including 8 species, the rhizosphere and endogenous phosphorus-dissolving strains are 20 and 7 species respectively.6. Strain ability:(1) SN0502 is the highest in all rhizosphere nitrogen-fixing strains, the enzyme activity reach to 3390.79 nmolC2H4/H·Culture. RN0101 is the highest in all endophytic strains, the enzyme activity reach to 2917.34 nmolC2H4/H·Culture. (2) SP0205 dissolved phosphorus ability is the highest, but only 33.99 ug/mL. Futhermore, the dissolved phosphorus ability of endophytic strains is only reached 23.99 nmol C2H4/H-Culture (3) Among 74 phosphorus-dissolving strains,38 strains can show some ability of phytase, accounting for 51.35% of the total strain, the rhizosphere strain SPO110-2 reached the highest phytase activity about 191.03 ug/ml in all plant growth promoting rhizobacteria, the endophytic strain RPO101 reached the highest phytase activity about 96.15 ug/ml.(4) In all 127 strains, there are 52 strains showed obvious ability of producing siderophore, which including 44 rhizosphere bacteria strains and 8 endophytic strains. SN0203 is the most powerful siderophore producer, the numerical value of A/Ar reached 0.18.In a word, the diversity of rhizospheric bacteria associated with desert shrubs is high in the Western Ordos. Most strains have the high ability of nitrogen fixation and phosphate-solubilizing. This research can promote the understanding and recognition of the bacterial diversity of advantage or endangered plants of west ordos. It has the vital significance of desert functional microbial development, utilization, protection and soil desertification ecosystem restoration, providing the theory basis and technical support.