The Spacial Distribution Of Plant-associated Bacteria In Different Sandy Lands Of Minqin

This thesis focuses on the realization of the main desert plants in Minqin sandy area, the typical drought and desertification land in north-west of China. The study researches the genetic diversity of bacterial community and the spatial distribution through a combination of the high-throughput sequencing technologies and the classical culturable method. In this thesis, a systematical research is carried out about the spacial distribution of plant-associated bacteria dependent on different types of sandy lands, different host plants, different plantcompartment, as well as the relationship between the spacial distributions of plant-associated bacteria and the environment. The main results are as follows:1) The spacial distribution of soil bacteria in different sandy lands of Minqin is clearly elaborated after the research. From the different sandy lands, 382,306 virtual sequences are obtained with the high-throughput sequencing technologies, and their read lengths range from 396.22 to 397.15 bp. The sequence number of bulk soil bacteria is much higher than that in the rhizosphere, but the OTU number shows the opposite result. The dominant groups(relative abundance>5%) of the soil samples are Actinobacteria, Firmicutes, Proteobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Acidobacteria and Candidate_division_TM7, but the proportions are different in each sandy land and plant rhizosphere, and the proportion of Firmicutes in the bulk soil is significantly much higher.2) The results of the replicate sampling approach show that the distribution of microbial communities are decided primarily by the fact that whether there are plants in local area. The PCA results show that the bacterial community distribution are, to a larger extent, influenced by the bulk soil or the rhizosphere, while the sandy land types and the plant species are the secondary factors.3) The spacial distribution and the structure of the plant-associated bacteria are elaborated. There are 188 pure strains isolated, and the concentration of culturable bacteria ranges from 102 to 107 CFU/g. 103 strains of bacteria are isolated from the soil sites, which have 5 phylums and 23 genera. The dominant bacteria are the Streptomyces, which belong to the Actinobacteria. 86 representative strains are isolated from the plant roots and the leaves, which have 4 phyla and 27 genera. The Actinobacteria accounts for more than half of all the main bacteria groups(69.66%).The plant-associated bacteria abundance and the genetic diversity of the Mingqin sandy lands have different patterns. The abundance of plant-associated bacteria distributes with a result: fixed sandy land > semi-fixed sandy land > shifting sandy land, and the genetic diversity pattern in this way: fixed sandy land > shifting sandy land > semi-fixed sandy land. The plant-associated bacteria abundance falls in line with the genetic diversity of the different plant compartment in this way: bulk soil > rhizosphere > root > leaf.4) The relationship between the soil physicochemical property and the distribution of bacterial of Minqin sandy lands is identified. The physical and chemical properties of different sandy lands are studied, and the results show that the content of organic matter(SOM) in the bulk soil distributs is: fixed sandy land > semi-fixed sandy land > shifting sandy land. The SOM is significant positive correlation with the STC. The total nitrogen(STN), total phosphorus(STP) and K+ are positively correlated. The diversity and distribution of the bacterial community are significantly correlated with the pH, Sand, C/N. Firmicutes has extremely significant positive correlation with Sand and pH. The Bacteroidetes shows significant positive correlation with electrical conductivity(EC), Clay, and Silt. All of these reveal that the bacterial community distribution is closely related to the soil physicochemical property, and the Firmicutes has a higher proportion in the relatively bad environment. Bacteroidetes are mainly distributed in the soil with relatively high leveled nutrients.This research lays a solid foundation for plant-microorganism interactions, and the functional diversity of plant-associated bacteria on ecosystem of the future study. In addition, it proposes a new way to increase the salinity-alkalinity stress resistance of plants. This research still has great significance in maintaining or restoring biological diversity, combating land degradation and desertification and keeping the ecological balance of the ecological system.