Effects of Rhizosphere Microorganisms Associated with Suaeda Salsa on the Growth and Salt Stress Resistance of Alfalfa

Plant growth-promoting rhizobacteria (PGPR) are soil microorganisms that interact with plants to enhance growth and development. In the past, PGPR screening has primarily focused on isolates from the rhizosphere of the target plant, with salt-tolerant strains from saline alkali soil typically utilized for soil improvement or as backup strains, rather than as PGPR. Limited research has been conducted on the efficacy of selected salt-tolerant strains in promoting the rhizosphere of alfalfa (Medicago sativa L.). This study employed the salt-tolerant strain Bacillus tropicus (YJ33) as the subject of investigation in the rhizosphere of Suaeda salsa, utilizing indoor pot experiments to comprehensively investigate its influence on alfalfa growth. The findings shed light on the role and impact of microorganisms in saline alkali soil on the growth of non-native plant species such as alfalfa. The application of YJ33 resulted in a significant enhancement in biomass production (p < 0.05), plant height (p < 0.05), and antioxidant enzyme activity (p < 0.05) of alfalfa, while also leading to a significant reduction in malondialdehyde (MDA) content (p < 0.05) and promoting overall growth under salt stress conditions. Furthermore, inoculation with the strain significantly elevated the crude protein content(p < 0.05) of alfalfa and facilitated phosphorus absorption (p < 0.05).Additionally, this study demonstrated that inoculation with strain significantly increased the levels of soil nitrate nitrogen, ammonium nitrogen, and available phosphorus. Furthermore, the introduction of the inoculated strain had a notable impact on the abundance of Firmicutes, Proteobacteria, and Actinobacteria. These alterations in phyla closely mirrored the shifts observed in soil characteristics and alfalfa physiology following inoculation. The salt-tolerant and growth-promoting bacteria identified in this study have been found to enhance the stress resistance of alfalfa in saline-alkali conditions, as well as facilitate plant phosphorus uptake, improve soil microbial conditions, and optimize the utilization of nitrogen and phosphorus elements.