Abstract

To investigate the regulatory effects of salt-tolerant plant growth-promoting rhizobacteria (PGPR) on crop growth under salt stress and to identify superior bacterial resources for saline–alkaline soil improvement, the maize variety Ningdan 33 was used as the experimental material. Strain XJ-33, a salt-tolerant PGPR isolated from saline–alkaline soil in Ningxia, was selected for inoculation. Based on morphological observation, physiological and biochemical tests, and 16S rRNA gene sequencing, the strain was identified as Pseudomonas glycinae. This strain can tolerate extreme conditions of up to 10% NaCl and a pH of 11.0, and exhibits multiple plant growth-promoting traits, including the production of siderophores and indole-3-acetic acid (IAA), as well as ACC deaminase activity. The results showed that inoculation with XJ-33 significantly promoted the growth of maize seedlings under salt stress. Compared with the control, inoculated plants exhibited significant increases in plant height, root length, and biomass (both fresh and dry weights), with the most pronounced increments observed in shoot and root dry weights, which increased by 82.61% and 81.63%, respectively. Physiological and biochemical analyses revealed that leaf SPAD values, chlorophyll content, and nitrogen content increased by 15.00%, 13.18%, and 18.47%, respectively, following inoculation. Additionally, root activity (indicated by dehydrogenase activity) was significantly enhanced. In terms of stress physiology, inoculation improved the osmotic adjustment capacity of the plants; the levels of soluble sugars, soluble proteins, and proline in both leaves and roots increased significantly, whereas the malondialdehyde (MDA) content, an indicator of membrane lipid peroxidation, decreased significantly. Furthermore, the antioxidant enzyme system was positively modulated: superoxide dismutase (SOD) and catalase (CAT) activities were significantly elevated in both leaves and roots, while peroxidase (POD) activity decreased. In conclusion, strain XJ-33 exhibits robust salt tolerance and strong plant growth-promoting capabilities. It can alleviate salt-induced damage in maize by regulating osmotic balance, enhancing antioxidant defenses, and promoting nutrient uptake, thereby demonstrating significant application potential for saline–alkaline soil improvement and the development of microbial agents.

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