Screening Of Plant-promoting Bacteria From Puccinellia Tenuiflora And Its Promoting Effect On Rice Growth Under Salt Stress

Due to the influence of natural environment and human activities,the increasing trend of land salinization is one of the main reasons for land degradation.Salinization changes the soil characteristics,inhibits the growth and metabolism of plants,and causes crop yield to decrease under saline-alkali stress.As one of the important food crops,rice also faces the harm of saline-alkali stress.Therefore,it is of great significance to study the diversity of microbial communities in the rhizosphere of halophytes and to screen the halotolerant rhizobacteria for alleviating plant salt and alkali stress.In this study,high-throughput sequencing method was used to analyze the composition of bacterial community in rhizosphere soil of Puccinellia tenuiflora.and the salt-tolerant plant growth-promoting bacteria were isolated and screened.The effect of growth-promoting bacteria on rice seedlings was verified by pot experiments.The main research and results are as follows:（1）High-throughput sequencing method was used to analyze the bacterial community in non-rhizosphere soil and rhizosphere soil of Puccinellia tenuiflora.The results showed that the number of specific OTUs in rhizosphere soil of Puccinellia tenuiflora（RS）and non-rhizosphere soil（BS）in saline-alkali soil was 1918 and 1577,respectively,accounting for70.36%and 66.12%of the total OTUs of each sample,of which 808 OTUs were shared by the two samples.The bacterial abundance of rhizosphere soil and non-rhizosphere soil of Puccinellia tenuiflora in saline-alkali soil was significantly different.The richness and species diversity of bacteria in rhizosphere soil of Puccinellia tenuiflora were higher.At the genus level,Oceanisphaera and Rhodobium occupies an absolute advantage in the rhizosphere soil of Puccinellia tenuiflora,while Rubricoccus occupies an absolute advantage in the bacterial community of non-rhizosphere soil in saline-alkali soil.（2）In order to screen out the growth-promoting strains with the ability of phosphate-solubilizing,IAA-producing,ACC-deaminase,and iron-carrier from the rhizosphere soil of Puccinellia tenuiflora,the strain H5 with strong growth-promoting ability was screened through the screening of growth-promoting characteristics and inoculated in the rhizosphere soil of rice through pot experiment.The maximum phosphorus solubility of strain H5 was 1344mg/L,and the maximum phosphorus solubility was 1432 mg/L under 0.15 mol/L Na Cl salt concentration.When the tryptophan concentration was 500μg/m L,the IAA synthesis reached the highest level of 10.06μg/m L.Under the condition of no stress,the ACC deaminase activity of H5 was 499.70 nmolα-KB mg^-1h^-1,which was reduced to 199.36 nmolα-KB mg^-1h^-1under the influence of 0.15 mol/L Na Cl salt concentration,and the relative content of iron carrier was 64.90%.（3）The growth promoting effect of strain H5 was further tested by pot experiment.Under the two conditions of no stress and salt stress,the biomass after inoculation with strain H5 was significantly increased,and the contents of chlorophyll,soluble protein and proline in the leaves of rice seedlings were significantly increased.The activities of malondialdehyde（MDA）and various antioxidant enzymes,such as superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）,were significantly decreased,indicating that a series of stress reactions caused by salt stress in rice after inoculation with strain H5 were slowed down,and a large amount of reactive oxygen species accumulated due to stress were reduced,thus promoting the growth and metabolism of rice.In this study,a halophyte-promoting rhizobacteria strain with salt tolerance was screened,which could alleviate the harm of salt stress in rice and promote the normal growth and metabolism of rice,providing a theoretical basis for further study on the ability of halophyte-promoting rhizobacteria to alleviate salt stress in plants.