Screening Of Plant Growth Promoting Rhizobacteria In Sesbania Cannabina And Its Effect On Promoting Growth And Salt Tolerance

As we all know,salinization can change the biological characteristics and physicochemical properties of soil,inhibit plant growth,and seriously restrict the development of agricultural economy and the improvement of ecological environment in the Yellow River Delta.In recent years,the relevant staff has begun to pay attention to the use of biological methods,such as domestication of salt-tolerant plants,crop rotation,application of bio-organic fertilizers and so on,to improve and utilize the saline-alkali land in the Yellow River Delta.Among them,Sesbania cannabina,a salt-tolerant plant,has been introduced to the Yellow River Delta as a pioneer crop of saline-alkali land improvement.However,the effect of the combination of S.cannabina and related functional rhizosphere microorganisms on improving saline soil is not clear,and the mechanism of rhizosphere growth-promoting microorganisms on the salt tolerance of S.cannabina needs to be further explored.Therefore,this study screened and identified the rhizosphere growth-promoting bacteria from the rhizosphere soil of the halophyte S.cannabina in the saline-alkali area of the Yellow River Delta in China,and tested their growth-promoting and salt tolerance properties.The nitrogen-fixing bacteria,phosphorus-dissolving bacteria,and potassium-dissolving bacteria in the rhizosphere soil of S.cannabina were isolated by selective culture and dilution coating plate method.Then nitrogen fixation,phosphorus dissolution,potassium dissolution,IAA production,ACC deaminase production,siderophore production and salt tolerance of the strains were measured,and comprehensively screened strains with excellent traits.Their effects of growth-promoting and salt tolerance of corn and S.cannabina under salt stress were verified respectively by pot experiments of vermiculite and soil,and the effect of different bacterial treatments on the microbial community structure of plant rhizosphere were explained by high-throughput sequencing technology.This study provides a theoretical basis for the field application of S.cannabina in improving saline soil.The main results are as follows:A total of 105 PGPR were isolated from the rhizosphere soil of S.cannabina.After comprehensive screening and analysis of their ability of growth-promoting and salt tolerance,two strains with multiple promoting properties and salt tolerance of 15%were obtained.They were identified as: N102 belongs to Enterobacter soli,K64 belongs to Enterobacter aerogenes.The seed germination test of S.cannabina showed that PGPR strains N102 and K64 could significantly increase the germination rate,shoot length and root length of S.cannabina compared with the treatments without applying bacteria,which also preliminarily verified the growth-promoting effect of strains N102 and K64.The effect of strain N102 on the growth of corn under different concentrations of salt stress was verified by pot experiments of vermiculite.The specific manifestation is that the inoculated strain N102 increased the plant height,root length,dry weight above and below the ground and chlorophyll content of corn under all salinity levels.Especially under 50 m M Na Cl stress,inoculated strain N102 significantly increased the plant height,root length,dry weight above and below the ground and chlorophyll content by 9.4%,25.7%,24%,29.6% and 4.5%,respectively.By pot experiments of soil,we evaluated the growth-promoting effect of single high-efficiency rhizobacteria,endophytic bacteria and their mixed strains on the halophyte S.cannabina under salt stress(0,200,300 and 400 m M Na Cl)in the greenhouse.The results showed that the S.cannabina obtained the maximum growth at the concentration of 300 m M Na Cl.Compared with the single inoculated rhizosphere and endophytic strains,co-inoculation could significantly promote the growth of plant height,dry weight above and below the ground and the number of nodules,increase the chlorophyll content,antioxidant enzyme activity and proline content,in addition,reduce the accumulation of MDA.By high-throughput sequencing technology,the effect of different bacterial treatments on the bacterial community structure of S.cannabina rhizosphere under salt stress(0,300 and 400 m M Na Cl)in greenhouse was explored.The results showed that compared with the treatments without applying bacteria,the application of different bacterial treatments has increased the richness and diversity of bacterial community in the rhizosphere soil of S.cannabina under different salinity levels.Among them,the richness and diversity of bacterial community of the co-inoculation of rhizosphere strain K64 and endophytic strain SC35 were significantly better than that in the treatment of single inoculation by applying different bacterial treatments.Secondly,compared with the control,the relative abundance of Proteobacteria and Bacteroides was increased at the phylum level,and Sphingomonas,Pontibacter and Massilia were increased at the genus level.In summary,this study screened PGPR with various growth-promoting traits and salt tolerance from the rhizosphere soil of S.cannabina,a salt-tolerant plant in the Yellow River Delta.Taking Enterobacter soli N102 and Enterobacter aerogenes K64 with the best comprehensive growth-promoting effect as the research objects,verified the significant growth-promoting effect of these two rhizobacteria on corn and S.cannabina under salt stress.Clarified the physiological mechanism of rhizosphere and endophytic bacteria in promoting plant growth under salt stress.Showed the potential of using rhizosphere and endophytic bacteria to promote plant growth,repair salt stress damage and regulate rhizosphere microecology in salt environment.They provided good strain resources for the development of bio fertilizer in saline-alkali land.