| In this study,the rhizosphere soil of Lycium ruthenicum grown in saline alkali soil in Shanshan County,Xinjiang was used as the research material,and the diversity and difference of rhizosphere microorganisms were analyzed by macrogenome sequencing technology.Based on the traditional culture technology,the dominant strains in rhizosphere soil were analyzed,and the bioactive salt tolerant rhizosphere growth promoting bacteria(PGPR)of Lycium ruthenicum were isolated.Pot experiment was conducted to explore the growth promoting effect of salt tolerant rhizosphere growth promoting bacteria on the seedlings of Lycium ruthenicum,Cotton and Arabidopsis under salt stress.The combination of two bacteria was determined through antagonistic reaction test to explore the effect of salt stress on the growth of host and non host plant seedlings,so as to provide excellent strains for the development of biological bacterial fertilizer and the improvement of soil extreme environment.1.Analysis of physicochemical properties of rhizosphere soil of Lycium ruthenicum in Shanshan areaThe physical and chemical properties of rhizosphere soil of Lycium ruthenicum in Shanshan county showed that the p H of rhizosphere soil was 8.86,the total salt content was 0.838 mg/g,the content of organic matter in rhizosphere soil was 2.66 g/kg,the content of total nitrogen was 0.16 g/kg,available phosphorus and 0.556 mg/g.The rhizosphere soil of Lycium ruthenicum is a typical saline alkali soil with organic matter,serious deficiency of nitrogen and phosphorus and imbalance of trace elements.2.Analysis of metagenome sequencing resultsMacrogenome sequencing technology was used to analyze the bacterial population diversity in the rhizosphere of Lycium ruthenicum.19 phyla were detected,including 8dominant phyla,which were Proteobacteria 14.97%,Actinobacteria 12.98%,Acidobacteria 6.91%,Curvularia 6.58%,Rokubacteria 2.51%,Blastomonas 2.32%Tectomicrobia(1.06%)and Planctomycetes(2.94%)are the unique phyla of rhizosphere bacteria of Lycium ruthenicum in Shanshan County,and the abundance of the other 11 phyla is less than 1%.In addition,bacteria unclassified accounted for 32.87%,which has the possibility of potential new species.At the genus level,it is found that 25% of the genera are Actinomycetes,17% of the genera are Chloroflexi and Acidobacteria,and 6%of the genera are Deltaproteobacteria and Rokubacteria.3.Isolation and growth promoting characteristics of salt tolerant rhizosphere growth promoting bacteria of Lycium ruthenicumIn this study,110 strains of rhizosphere microorganisms of Lycium ruthenicum were screened,and 10 strains of salt tolerant rhizosphere microorganisms were obtained through salt tolerance screening.The growth promoting characteristics of the 10 salt tolerant rhizosphere bacteria were analyzed.It was found that the 10 salt tolerant rhizosphere growth promoting bacteria had different abilities of phosphorus dissolution,iron carrier production,auxin and nitrogen fixation.The amount of dissolved phosphorus of strain HQA2 reached 52.63mg/L,and the ability to produce IAA was 54.21mg/L.Ten salt tolerant rhizosphere growth promoting bacteria were identified by molecular identification of 16 S r RNA gene sequence,belonging to 6 genera and sub genera.Strains HQA9,HQA4 and Bacillus haloolerans,HQA2,HQA4,HQA5,HQX56 and Bacillus rugosus,HQA8 and Bacillus subtilis subsp,HQA14 and Priestia megaterium,HQX34 and Bacillus paramycoides,and HQY4 and Pseudomonas putida had the highest homology.4.Effects of root irrigation with four salt tolerant rhizosphere growth promoting bacteria on the growth of plant seedlings under salt stressWe screened four salt tolerant rhizosphere growth promoting bacteria with the best comprehensive biological activities,such as phosphorus dissolving,iron producing carrier,auxin and nitrogen fixing ability,and carried out pot growth promoting experiment to study the growth promoting effect on black fruit medlar,cotton and Arabidopsis seedlings.The four salt tolerant rhizosphere growth promoting bacteria were HQA8,HQA9,HQX34 and HQX56,respectively.In the pot experiment,the growth promotion experiment of plant seedlings was carried out with single bacteria group and double bacteria group.Through the test of antagonistic reaction,the antagonistic strains can not be mixed,but can only be applied alone.There are three combined bacterial groups,namely HQA8+HQA9,HQA8+HQX56 and HQX34+ HQX56.Compared with the negative control,the application of four salt tolerant rhizosphere growth promoting bacteria could promote the growth of Lycium ruthenicum seedlings under salt stress to varying degrees.The fresh weight,dry weight,plant height,number of leaves and chlorophyll content of Lycium ruthenicum seedlings treated with strain HQA8 increased by 45.7%,121.4%,164.5%,56.2% and 22.6% respectively(P < 0.05),The number of leaves and plant height of strain HQX34 increased by 55.3% and 46.5% respectively(P < 0.05).Compared with the single bacteria treatment group,the combined bacteria treatment significantly promoted the growth of Lycium ruthenicum,cotton and Arabidopsis seedlings under salt stress.Under salt stress,the activities of antioxidant enzymes(SOD and POD)in the leaves of rhizosphere bacterial seedlings increased significantly compared with CK,positive control and negative control groups.Compared with the single strain treatment group,the plant antioxidant enzyme activity of strain HQA8+HQA9 changed the most in the strain HQA8 treatment group and the combined strain treatment group.Compared with CK in the blank control group,the SOD activity of Lycium ruthenicum seedlings treated with single strain HQA8 and combined strain HQA8+HQA9 increased by 45.03% and 63.01% respectively,and the POD activity increased by 49.85% and 57.95% respectively.The growth promoting effect of combined bacteria on plant seedlings is better than that of single bacteria group,in which the growth promoting effect of single bacteria group HQA8 and combined bacteria group HQA8+HQA9 is the best. |
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