Plant growth-promoting rhizobacteria Halomonas alkaliantarcticae M23 promotes the salt tolerance of maize by increasing the K+/Na+ ratio, antioxidant levels, and ABA levels and changing the rhizosphere bacterial community

Soil salinity is a global issue threatening crop growth and yield. Salt-tolerant plant growth-promoting rhizobacteria (PGPB) can survive in high-salinity environments and help plants adapt to stress, thus serving as an effective measure to mitigate salt stress. In this study, a salt-tolerant plant growth-promoting bacterium, Halomonas alkaliantarcticae M23 (M23), was isolated from the rhizosphere soil of the salt-tolerant plant Suaeda salsa. This study characterized the effects of M23 on maize growth, salt stress response, and the composition and structure of rhizosphere soil microorganisms, and preliminary explained the mechanism by which M23 enhances maize salt tolerance. M23 can tolerate up to 14% NaCl, produce auxin, and exhibit the ability to absorb Na+ and accumulate K+ under salt stress. This study also measured amino acid production by M23 under different salinity conditions and found that M23 could mainly produce glutamic acid (Glu), glutamine, proline, and lysine, with their contents significantly increasing as salinity rises. Inoculating maize with M23 enhances the salt tolerance by increasing the K+/Na+ ratio, improving the antioxidant levels, and regulating its ABA levels in maize. Additionally, inoculating with strain M23 not only increases soil diversity but also alters the composition of bacterial communities in the maize rhizosphere soil. Most species were significantly enriched in saline soil treated with M23 at the phylum level. At the genus level, some salt-tolerant plant growth-promoting bacteria such as Bryobacter, Nocardioides, and Micromonosporaceae were also significantly enriched. Halomonas alkaliantarcticae M23 could promotes the salt tolerance of maize by increasing the K+/Na+ ratio, antioxidant levels, and ABA levels and changing the rhizosphere bacterial community. This study demonstrates that M23 has great potential in promoting plant growth in saline-alkali soils.