Study On Bacterial Diversity Of Vegetation Rhizosphere Soil In Different Desert Grassland Areas

The natural ecosystems in western China are relatively fragile,and confronted with the conspicuous problems of land desertification and vegetation degradation.It is significant to strengthen protection of the desert grassland plants and improve the biodiversity of desert ecosystems.The relationship and interaction between the rhizosphere soil microorganisms and desert grassland plants are very important to maintain the balance of desert ecosystems.In order to study the diversities of the rhizosphere microorganisms of desert grassland plants,explore their effects on the growth of desert grassland plants,and maintain stabilities of the desert ecosystems,two different types of desert grassland and main plants species in western China were selected as the research objects.High-throughput sequencing analysis and spread plate count methods were used to determine the diversities of the microorganisms from the desert grassland soil and main desert plants rhizosphere soils.The physicochemical properties of the different soil types and correlation between the main physicochemical indexes and the bacterial diversities were also analyzed.The main research contents were as follow:The bacteria communities of the desert steppe soil and Peganum harmala L.rhizosphere soil in Baiyin were studied by high-throughput sequencing analysis.The bacteria community of the desert steppe soil consisted with 23 phyla,43 classes,80 orders,167 families and 344 genera.The community of the Peganum harmala L.rhizosphere soil included 24 phyla,44 classes,88 orders,179 families and 400 genera.The dominating phyla were Actinobacteria,Proteobacteria,Bacteroidetes,Acidobacteria,Gemmatimonadetes,Verrucomicrobia,Chloroflexi,Firmicutes,Cyanobacteria and Planctomycetes,which accounted for 94.35% and 95.90% of the total bacteria in these two kinds of soils,respectively.The major genera of the Peganum harmala L.rhizosphere soil contained Flavisolibacter ?Adhaeribacter ?Pontibacter?Aridibacter?GP4?Spartobacteria,specially,but the major genera of the desert steppe soil contained Blastococcus,Streptomyces,Arthrobacter,hyrogenophaga,Thermasporomyces and Nocardioides.By using plate dilution method,the total culturable bacteria accounts of the desert steppe soil and the Peganum harmala L.rhizosphere soil were measured to be about8.90×106 cfu·g-1 and 1.46×107 cfu·g-1 respectively.Thirty three strains were isolated from the two soils.The culturable bacteria in desert steppe soil contained six genera of Proteobacteria,Firmicutes and Actinobacteria,with Arthrobacter,Bacillus,Pseudomonas and Brevibacterium being the dominant genera.The culturable bacteria in Peganum harmala L.rhizosphere soil included eight genera of Proteobacteria,Firmicutes and Actinobacteria,with Brevibacterium,Bacillus,Pseudomonas and Brevundimonas being the dominant genera.The bacteria communities of the desert steppe soil and the rhizosphere soil of three kinds of desert plants including Caragana korshinskii,Salix psammophila and Artemisia sphaerocephala,in Yulin were studied with high-throughput sequencing analysis.The dominant bacteria of the desert steppe soil contained 22 phyla,44 classes,86 orders,176 families and 455 genera.The dominant bacteria of the Caragana korshinskii rhizosphere soil contained 25 phyla,46 classes,92 orders,198 families and 499 genera.The dominant bacteria from Salix psammophila rhizosphere soil contained 23 phyla,45 classes,91 orders,182 families and 461 genera.The dominant bacteria of the Artemisia sphaerocephala rhizosphere soil contained 24 phyla,45 classes,92 orders,178 families and 465 genera.The abundance and bacterial diversities were significantly different between the different plant rhizosphere soils and the non-rhizosphere soils.At phylum level,the desert steppe soil bacteria mainly belonged to Actinobacteria,Proteobacteria,Acidobacteria,Firmicutes,Bacteroidetes,Gemmatimonadetes and Chloroflexi,which accounted for 96.22% of the total bacteria.The bacteria of the rhizosphere soils of Caragana korshinskii,Salix psammophila and Artemisia sphaerocephala mainly contained Proteobacteria,Actinobacteria,Firmicutes,Bacteroidetes,Acidobacteria,Planctomycetes,Chloroflexi,Gemmatimonadetes,which accounted for 96.16%,96.85% and 95.72% of the total bacteria of the three rhizosphere soils,respectively.At genus level,the dominantbacteria genera of desert steppe soil were identified as Pseudomonas,Nocardioides,Arthrobacter,Marmoricola,Sphingomonas,Gp6,and Aciditerrimonas.The dominant bacteria genera of Caragana korshinskii rhizosphere soil were identified as Nocardioides,Sphingomonas,Pseudomonas,Marmoricola,Arthrobacter,Phycicoccus,Gp6,Altererythrobacter and Acinetobacter.The dominant bacteria genera of the Salix psammophila rhizosphere soil were identified as Arthrobacter,Sphingomonas,Pseudomonas,Nocardioides,Marmoricola,Lysobacter and Rhizobium.The dominant bacteria genera of Artemisia sphaerocephala rhizosphere soil were identified as Arthrobacter,Sphingomonas,Pseudomonas,Nocardioides,Marmoricola,Gp6 and Lysobacter.The total culturable bacteria amounts were measured to be 6.45×106 cfu·g-1?9.32×106 cfu·g-1?7.45×106 cfu·g-1 and 1.12×107 cfu·g-1 in desert steppe soil and Caragana intermedia intermedia,Salix cheilophila,Artemisia desertorum rhizosphere soils,respectively.Sixty-nine strains were isolated from the different soils.The isolated bacteria belonged to the nineteen genera including Bacillus,Brevibacterium,Microbacterium,Streptomyces,Sphigobacterium,Chyseobacterium,Cellulosimicrobium,Flaavobacterium,Lysobacter,Arthrobacter.Stenotrophomons.The physical and chemical properties of the two different desert steppe soils and the rhizosphere soils of Caragana korshinskii,Salix cheilophila and Artemisia sphaerocephala were determined,which included the water content,pH,the total nitrogen,the total phosphorus respectively.The results showed that the soils were alkaline and the water contents were lower.There were significant differences in the physical and chemical characteristics(p<0.05)between the desert steppe soil and the plant rhizosphere soils except for pH.The physical and chemical characteristics of the rhizosphere soils such as the water content,total nitrogen,available nitrogen,total phosphorus,available phosphorus,total potassium,available potassium and soil enzymes were significantly higher than those of the surrounding non-rhizosphere soils(p<0.05).There are some differences in physicochemical indexes of different plant rhizosphere soils in the same area.The nutrient contents of the Caragana korshinskii rhizosphere soil of were significantly higher than those of the Caragana korshinskii,Salix cheilophila and Artemisia sphaerocephala rhizosphere soils.Based on the correlation analysis between the alpha index of the microbial communities and soil physical and chemical characteristics,the contents of the total nitrogen,total phosphorus and available potassium of the soils were positively correlated with the Shannon index(p<0.01),which suggested that the microbial diversities increased with the increase of the total nitrogen,total phosphorus and available potassium contents of the soils.The available nitrogen of the soils was positively correlated with the Chao1 index(p<0.01),and positively affected the soil microbial abundance.The total nitrogen,available nitrogen,total phosphorus and available potassium are the main factors which affect the soil microbial diversity and richness of the soils.