Effects Of The Combined Application Of γ-PGA Producing Bacteria And Monosodium Glutamate Residue On Growth And Quality Of Lettuce In Heavy Metal Cd Contamination Soil

Due to the excessive application of pesticides and fertilizers,as well as frequent industrial activities,heavy metal pollution in arable soil in China is severe,especially cadmium(Cd)pollution,showing an increasing trend.Many studies have found that plant growth promoting bacteria play an important role as microbial inactivators in promoting plant growth and blocking heavy metal transfer.This study investigated the synergistic effect of monosodium glutamate residue on polyglutamic acid producing strain W25 through in vitro shaking bottle experiments and pot experiments,as well as the combined application of the two on the growth and quality of lettuce(Lactuca sativa L.),soil physicochemical properties,and rhizosphere microbial community under heavy metal contaminated soil conditions.The results indicate that:1)Monosodium glutamate residue can enhance the ability of Bacillus amyloliquefaciens W25 to produce polyglutamic acid.Under Cd pollution conditions with a concentration of 3mg/L,the application of monosodium glutamate residue can increase the content of polyglutamic acid in soil filtrate by about 1.1 times and significantly reduce the content of Cd ions in the filtrate.2)The combination of strain W25 and its treatment with monosodium glutamate residue can alleviate the stress of heavy metals on the growth process of lettuce,increase the edible tissue biomass of lettuce by 50.8%,and reduce the Cd content in lettuce roots and leaves by 11% and22.3%,while increasing the chlorophyll and vitamin C content in lettuce leaves by28.7% and 93.8%.3)The combined application of monosodium glutamate residue and strain W25 reduced the content of available Cd in soil,increased soil p H and enzyme activity.4)The combined application of monosodium glutamate residue and bacterial strains increased the relative abundance of Proteobacteria and Bacteroidea in the rhizosphere soil of lettuce,enriched the Luteimonas genus of Proteobacteria and Flavobacterium genus of Bacteroidea,and Luteimonas genus became the main marker species in its rhizosphere soil.