Regulation Of Plant Growth Promoting Bacteria On Soybean Growth Under Salt Stress

Soil salinization is a typical soil obstacle factor,which restricts soil sustainable utilization and agricultural production.It is of great theoretical and practical significance to improve crop salt resistance to increase crop yield and expand agricultural production.How to enhance the salt resistance of crops has become an important subject of sustainable and efficient development of Chinese agriculture.Plant growth-promoting bacteria generally have the function of promoting plant growth and improving plant stress resistance.Plant endophytes are a kind of microorganisms that colonize in healthy plant tissues and symbiosis with host plants without causing obvious lesions.Some endophytes also have plant growth-promoting properties,but the effect of using endophytes with plant growth-promoting ability to regulate salt tolerance of soybean remains unclear.In this study,combined with the plant growth promotion potential of the strain under salt stress,we screened out the plant endophytic bacteria with salt tolerance.On this basis,the regulation effects of soaking and root irrigation of the above strains on soybean seed germination,seedling growth,typical physiological characteristics and nutrient accumulation under salt stress were further investigated.Meanwhile,the relationship between the change of soil properties and plant growth characteristics under salt stress regulation was discussed in combination with the change rule of soil typical physical and chemical properties under the regulation of the above strains.It provided a new method for improving plant resistance to salt stress and promoting plant growth.The main research results are as follows:(1)The growth ability and plant growth promotion potential of seven strains of endophytic soybean bacteria screened in our laboratory under salt stress were systematically investigated.The results showed that: strains Klebsiella pneumoniae L15,Klebsiella pneumoniae L17,Acinetobacter calcocaceticus N18 could grow in LB medium containing 1-6%(m/v)Na Cl.In addition,at 4% Na Cl concentration,inoculated strains L15,L17 and N18 still showed good growth promoting ability,indoleacetic acid production ability L15>L17>N18,iron carrier production ability L17>L15>N18,phosphorus solubilization ability N18>L15>L17.Combined with the salt-tolerant and growth promoting ability of the strain,the strain L15 with the strongest indole-acetic acid production ability,the strain L17 with the strongest ferric carrier production ability and the strain N18 with the strongest phosphorus solubing ability were selected for follow-up tests under 4% salt stress.(2)The results of germination test showed that: under 0.8% NaCl stress,soybean seed germination potential increased by 63.15%,47.36% and 42.09%,germination rate increased by36.66%,30.30% and 24.24%,germ length increased by 44.32%,38.97% and 21.65%,and fresh weight increased by 36.17%,31.91% and 23.40% after inoculation with strains L15,L17 and N18,compared with that without inoculation.These results indicated that strains L15,L17 and N18 could significantly improve germination potential,germination rate,germ length,fresh weight,germination index and vigor index of soybean seeds under salt stress.In addition,the results of hydroponics test showed that: under 0.8% salt stress,the plant height and root length of soybean treated with inoculated strains L15,L17 and N18 were significantly higher than those treated with uninoculated strains,indicating that soaking with the above strains could alleviate the inhibition of salt stress on soybean growth.(3)The growth physiological characteristics and nutrient accumulation of soybean seeds in actual saline soil were investigated under the condition of inoculation.Pot experiment results showed that inoculated strains L15,L17 and N18 could increase the content of chlorophyll a,chlorophyll b and total chlorophyll in soybean seedlings.In addition,by inducing the increase of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in soybean,the above three enzymes activities of the inoculated strain under 0.8% salt treatment were higher than those of the uninoculated strain.The strain could also reduce the accumulation of membrane lipid peroxidation product MDA under salt stress,thus alleviating the oxidative stress caused by salt environment on soybean seedlings and enhancing their salt tolerance.In 0.8% saline soil,inoculated strains L15,L17 and N18 increased total nitrogen content by 29.56%,19.89% and 15.05%,and total phosphorus content by 26.53%,14.03% and 6.79%,respectively,indicating that inoculated growth-promoting bacteria could improve the accumulation of nutrient content in soybean seedlings.At the same time,compared with blank control,inoculated strains L15,L17 and N18 decreased p H value by 0.61,0.43 and 0.29 units,electrical conductivity decreased by 13.15%,5.26% and 7.89%,and soil alkalihydrolytic nitrogen content increased by 3.81%,2.54% and 1.54%,respectively.The available phosphorus content in soil was increased by 5.09%,3.91% and 2.48%,respectively.These results indicated that inoculation with plant growth-promoting bacteria could reduce soil salt content and increase soil alkali-hydrolyzed nitrogen and available phosphorus content.In addition,correlation analysis showed that soybean seedling height was positively correlated with soil organic matter,available phosphorus,total nitrogen and total phosphorus,and negatively correlated with soil p H and electrical conductivity,indicating that plant and soil nutrient contents had a significant promoting effect on improving soybean salt tolerance,and reducing soil p H and electrical conductivity in a certain range was conducive to the growth of seedlings.