The Spacial Distribution And Function Of Plant-associated Bacteria From Caragana Fabr.in Desert Areas

Plant-associated bacteria were significant portions of plant micro-ecosystems,which have an important impact on the plant growth,improving plant resistance and soil fertility.High throughput sequencing and culture method were used in this study to investigate the structure of composition and potential plant growth promoting(PGP)traits of bacteria associated with Caragana in the northwest China.The main research results were as follows:1.The spatial distribution characteristics of bacteria under different microenvironment of Caragana Fabr were revealed.From the rhizosphere soil and leaf samples of Caragana Fabr.,we obtained 453,536 quality sequences and 14288 OTU.Of these,the sequence and OTU number of rhizosphere bacteria was significantly higher than phyllosphere.The richest group bacteria of rhizosphere and phyllosphere were Proteobacteria,Cyanobacteria,Actinobacteria,Acidobacteria,Bacteroidetes,Chloroflexi and Gemmatimonadetes.Proteobacteria was the most abundant in rhizosphere soil,whereas Cyanobacteria dominated in phyllosphere.Based on the optimized procedures of isolation and cultivation,a total of 116 cultivable bacteria strains associated with Caragana Fabr were detected and considerable population size that ranged from 103 to 105 cfu g-1 FW was monitored.The highest proportion of endophytic bacteria in root tissue was represented by Proteobacteria,while in leaves tissue was represented by Firmicutes.In addition,the diversity and abundance of root endophytic bacteria were significantly higher than leaves.The NMDS results showed that different microhabitat was an important influence factor for microbial structures.2.The distribution characteristics of bacteria from different species of Caragana Fabr were showed.The bacterial community had no obvious difference among 6 species of Caragana rhizosphere and phyllosphere,but there was a significant difference in abundance.In C.korshinskii 70% phyllosphere bacteria were classified to Cyanobacteria,while in C.roborovskyi only 5% bacteria belonged to Cyanobacteria.Bacteroidetes was abundance in C.roborovskyi and C.tibetica,but lowest in C.korshinskii phyllosphere.16S rDNA phylogenetic analysis showed that the endophytic bacterial community is very difference between 6 species of Caragana Fabr.The diversity of endophytic bacteria in the following order: C.brevifolia?C.arborescens?C.roborovskyi?C.korshinskii and C.tibetica ? C.microphylla.Furthermore,the Bacillus was detected in all Caragana tissues.3.The spatial distribution characteristics of bacteria from C.microphylla in different desert areas were elaborated.A total of 51 endophytic bacteria were isolated and identified from 5 desert areas.They are Firmicutes,Actinobacteria,proteobacteria and Bacteroidetes.In addition,72.5% endophytic bacteria belonged to Firmicutes.Furthermore,the community population was 3.03×104-5.53×106 cfu g-1 FW.The endophytic bacteria community of C.microphylla is very difference between 5 desert areas.On the whole,the diversity of endophytic bacteria in semi-humid area(ZGT)was higher than semi-arid(YC/NM/WNT)and arid area(MQ).4.The relationship between soil characteristics and the distribution of bacteria from 6 species of Caragana Fabr were explained.The results of Caragana plant rhizosphere and bulk soil physicochemical properties showed that the total nitrogen(TN),total phosphorus(TP)and organic matter(SOM)in rhizosphere were higher than bulk soil.RDA analysis showed that rhizosphere bacteria community distribution was significant positively with soil TP,Clay and Silt.5.The potential plant growth promoting(PGP)traits of endophytic bacteria isolated from Caragana Fabr were studied.The endophytic bacteria isolates from Caragana have potential plant growth promoting(PGP)traits: solubilization inorganic phosphate,nitrogen fixation,produce indoleacetic acid(IAA),synthesize siderophores and 1-aminocyclopropane-1-carboxylate(ACC)deaminase.The proportion of nitrogen fixation(82.03%)and synthesize ACC(60.07%)bacteria were highest.Of these,several strains can synthesis acdS and nifH genes.In addition,most of the functional strains belonged to Bacillus,Paenibacillus,Brevibacterium,Variovorax and Phyllobacterium which could be regarded as a good microorganismagents.The results of our study demonstrated that the bacteria associated with Caragana were riched in genetic and functional diversity.These results are of great valuable for further research on the relationship between bacteria and its host plant,exploration and application plant-associated bacteria resources as well as to maintain and restore the diversity of desert ecosystem.In addition,these isolated strains have a variety of functions that can provide a valuable basis for subsequent applications to improve the adaptation of plants in desertification regions.