Effects of endophytic bacteria on antioxidant enzymes SOD and CAT, root anatomical structure of soybean seedlings under salt stress

To explore the effects of endophytic bacteria on salt tolerance of soybean seedlings and to provide a biological strategy for alleviating salt stress damage in soybean production, ‘Xudou 20’ (a moderately salt-sensitive cultivar widely cultivated in the Huang-Huai-Hai region) was used. Endophytic strains 131 and 137 were investigated via pot experiments under salt stress with bacterial suspensions at three dilution ratios (1:1, 1:2, and 2:1, bacterial suspension: sterile water). Beyond antioxidant enzymes and root anatomy, we evaluated plant height, chlorophyll content, and malondialdehyde (MDA) levels. Strains 131 and 137 were identified as Enterobacter ludwigii and Bacillus cereus , respectively. Inoculation increased SOD and CAT activities (maximum SOD: 14.89 U·g − 1 ·FW, maximum CAT: 1910 U·g − 1 ·min − 1 at 50 mmol/L NaCl), increased chlorophyll content, reduced MDA accumulation, alleviated root growth inhibition, and maintained root epidermal integrity. Strain 131 most effectively mitigated salinity stress-induced chlorophyll loss and MDA accumulation, while strain 137 demonstrated better growth promotion in terms of plant height and root length. These endophytic strains improve soybean salt tolerance by regulating antioxidant enzymes, osmotic regulation, and photosynthetic efficiency, thus offering a biological measure for soybean production in salinized areas.