Response Mechanism Of Rhizosphere Soil Bacteria Of Desert Plants To Different Drought Conditions And Dune Types

Desertification as a global environmental problem has attracted more and more attention.Studying soil microbial community structure and soil-microbe-plant interactions in desert areas is of great significance for the prevention and control of desertification.In this study,four sites with different drought conditions and three different types of dunes in the desertification area of northern China were selected,and the rhizosphere and bulk soils of the dominant desert plants distributed in the environment were collected.The characteristics of soil properties and the distribution characteristics of bacterial community structure under different drought conditions,different dune types and different plant species were studied by high-throughput sequencing and cultivable methods.The interaction between plant-microbe-soil was analyzed.The primary results are as follows:1.The characteristics and changing rules of soil in different drought conditions and dune types were explained.Soil physicochemical properties of rhizosphere and bulk soil were analyzed.The results showed that the soil pH,EC and ion contents(Ca²⁺,K⁺,Na⁺)decrease significantly with the increase of aridity index,while soil nutrient contents?TOC,TN,TP?increased significantly.Fixed dune has higher soil nutrient content and ion content than semi-fixed and moving dune.Plant rhizosphere soil generally has higher soil nutrient contents and higher bacterial community quantity.There are significant differences in soil properties between different plants in rhizosphere.2.The response mechanism of soil non-culture bacterial community to different drought conditions and dune types was revealed.MiSeq high-throughput sequencing method was used to study the rhizosphere and bulk soil bacterial communities of Caragana microphylla distributed at all research sites.The results showed that the bacterial community in this study was mainly composed of Firmicutes,Actinobacteria,Proteobacteria,Acidobacteria,Chloroflexi,Bacteroidetes and Pluntomycetes.The most dominant genus includes Lactococcus,Bacillus,Pseudarthrobacter,Solibacillus and Pseudomonas.The relative abundance of Acidobacteria,Chloroflexi and Gemmatimonadetes showed significant differences among different sites.Their relative abundance tends to increase with aridity index?AI?.The relative abundance of Bacteroidetes in rhizosphere soil at the four different sites was significantly higher than that in bulk soil.For the different types of dunes,the relative abundance of Actinobacteria and Bacteroidetes in rhizosphere soil increased significantly as compared with bulk soil,while the relative abundance of Bacteroidetes,Gemmatimonadetes and Nitrospirae was significantly different among different types of dunes.PERMANOVA showed that drought conditions had stronger effect on bacterial community than rhizosphere at four sites.In three different types of dune,rhizosphere has stronger influence on bacterial community than dune type.Correlation analysis showed that at sites with different drought conditions,TOC,TN,Na⁺,followed by TP have the most significant influences on bacterial community composition.Acidobacteria,Gemmatimonadetes and Actinobacteria responded most strongly to physicochemical factors.In different types of dune,TOC and EC have the most significant influence on bacterial community composition,followed by pH and TP.Actinobacteria,Planctomycetes and Gemmatimonadetes had the most significant influence on the physicochemical factors.3.The response of the culturable bacteria in the rhizosphere of dominant desert plants to different drought conditions and dune types was established.It is showed that the bacterial community obtained by culturable methods was mainly composed of Firmicutes,Actinobacteria,Proteobacteria and Bacteroidetes.The proportion of Proteobacteria and Bacteroidetes in rhizosphere soil was significantly higher than that in bulk soil.At the level of genus,the diversity of rhizosphere bacteria was higher than bulk soil.The analysis of bacterial community and environmental factors indicated that richness was mainly positively correlated with soil nutrient content and aridity index,while diversity was positively correlated with pH,EC and ion content.4.Plant growth promoting bacteria?PGPB?that could promote plant growth and stress resistance were found.The plant growth promoting?PGP?traits of 398 strains of bacteria was determined.The results showed that the proportion of strains with PGP traits in rhizosphere was higher than bulk soil.This proportion increased with AI.It is also showed an increase trend from moving dune,semi-fixed dune to fixed dune.Firmicutes had a large number of strains with functions of nitrogen fixation,phosphorus dissolution and IAA production.Actinobacteria had the highest proportion of strains with functions of ACC deaminase production,and the strains with siderophore production were mainly distributed in Proteobacteria.Further analysis showed that 63 strains had multiple PGP functions,including 43 strains from rhizosphere and 20 strains from bulk soil.Co-culture with Arabidopsis seedlings showed that strains GC-3,HR-2,HR-3 and HR-5 significantly promoted the growth of Arabidopsis thaliana.This study combines high-throughput sequencing with culturable methods to systematically describe the changes and response mechanisms of soil bacterial communities under different drought conditions,different dune types and different plant rhizosphere effects,providing a theoretical basis for desertification control and vegetation restoration.The obtained multi-functional strains will be an excellent strain resource for promoting plant growth and improving plant stress resistance,and can be used as a high-quality microbial agent for vegetation restoration in desertification areas.