Isolation And Identification Of Salt-Tolerant Growth-Promoting Bacteria And Its Growth-Promoting Effect On Grape Seedlings Under Salt Stress

Grape（Vitis vinifera L.）is a significant economic fruit crop,but its growth and development can be seriously inhibited by soil salinization.However,Plant Growth-Promoting Rhizobacteria can help to promote plant tolerance to adverse environments through their metabolism and interaction with plants,which provides a new method for promoting saline-alkali soil treatment.This study focused on selecting salt-tolerant microorganisms from the rhizosphere soil of grapes in Dongying City,Shandong Province,which is known for its saline-alkali soil.To comprehensively screen for a salt-tolerant microorganism with excellent growth-promoting characteristics,we measured the production of indole-3-acetic acid（IAA）,1-aminocyclopropane-1-carboxylic acid（ACC）deaminase,phosphorus solubilization,silicate hydrolysis,and salt tolerance of microorganisms.After identifying the top-performing strain,we verified its growth-promoting effect on grape seedlings under salt stress.In addition,the high-throughput sequencing technology was utilized to analyze the changes of rhizosphere soil microbial communities.The main results are as follows:（1）A total of 130 strains were isolated in this study and one strain,Brevibacterium epidermidis S4-1,was preferably selected for its good salt tolerance and growth promotion,with silicate solubilising,IAA and ACC deaminase producing properties and salt tolerance up to 15%Na Cl.（2）The inoculation of strain S4-1 resulted in increased grape seedling biomass,particularly when subjected to 250 m M Na Cl treatment.Compared to Na Cl treatment,the inoculation of the strain under salt stress reduced yellowing and wilting of leaves and promoted the growth of grape seedlings.The height,root length,above-ground dry and fresh weight and below-ground dry and fresh weight of grape seedlings increased by 33.96%,27.74%,26.3%,33.97%,95.38%and 101.05%,respectively.（3）Inoculating grape seedlings with strain S4-1 has been found to enhance their antioxidant and osmoregulatory capacities when subjected to salt stress.Compared with Na Cl treatment,the inoculated strain under salt stress increased the antioxidant enzyme activity of grape seedlings,reducing the content of hydrogen peroxide（H₂O₂）and superoxide anion(O₂^·-)by 20.45%and 23.5%,respectively,alleviating oxidative damage;in addition,leaf and root electrolyte permeability were significantly reduced（P<0.05）.The inoculated strain induced more accumulation of soluble sugar,proline and soluble protein under salt stress,and maintained osmotic balance.（4）The inoculation of strain S4-1 resulted in varying degrees of increased soil enzyme activities in the inter-rhizosphere of grapevine under salt stress.Specifically,the strain significantly increased soil FDA hydrolase（90.20%）,urease（73.89%）,and catalase（89.73%）activities（P<0.05）.However,it had no significant effect on alkaline phosphatase and electrical conductivity.（5）Inoculating strain S4-1 under salt stress had a noticeable impact on the soil microbial community structure.Compared with Na Cl treatment,S4-1 under salt stress increased the diversity of microbial community,and the distribution of bacterial and fungal communities was significantly different among different treatments（P<0.05）.After inoculation of the strain under salt stress,at phylum level,the bacterial communities increased the relative abundance of Proteobacteria and Firmicutes;The fungal community increased the relative abundance of Ascomycota and Mortierellomycota.（6）Inoculating strains can help plants better resist salt stress by recruiting beneficial microorganisms.Inoculated strain S4-1 was significantly enriched with beneficial microorganisms such as Pseudomonas,Sphingomonas,and Podospora under salt stress.In summary,inoculation of strain S4-1 can improve the antioxidant capacity and osmoregulatory capacity of grape seedlings under salt stress,increase soil enzyme activity,influence the microbial community and recruit beneficial microorganisms to enhance resistance to salt stress and promote the growth of grape seedlings under salt stress.This study holds significant importance for improving the yield and quality of saline grapes.It lays the groundwork for exploring microbial resources and serves as a reference for future research on utilizing microorganisms to improve the salt tolerance of grape seedlings.