Co-inoculation with Sinorhizobium meliloti and Enterobacter ludwigii improves the yield, nodulation, and quality of alfalfa (Medicago sativa L.) under saline-alkali environments

Soil salinisation has become a global ecological and resource issue, which severely restricts the yield and quality of crops. This study analysed the effects of inoculation of Sinorhizobium meliloti GL1 and Enterobacter ludwigii MJM-11 on the yield, nodulation, and quality of alfalfa in a saline-alkali environment. The results of pot experiments showed that co-inoculation of alfalfa promoted its growth and improved the colonisation ability of rhizobia in the alfalfa roots and the activity of nodule nitrogenase. Furthermore, the expression of genes related to nodulation and nitrogen fixation were also upregulated. Co-inoculation also improved the antioxidant enzyme activity and osmotic regulation ability in alfalfa. The field experiment results demonstrated that after co-inoculation, the hay yield, crude protein, and phosphorus content of alfalfa increased by 26.12%, 24.32%, and 20.61%, respectively, whereas the contents of neutral detergent fibre and acid detergent fibre decreased by 10.83% and 11.87%, respectively, compared to the control. These results indicate that a good synergy exists between rhizobium and PGPR which can promote the growth and nodulation of alfalfa in a saline-alkali environment, and improve its yield and quality. This study establishes a theoretical foundation for the cultivation of alfalfa in saline-alkali soils, the development of microbial fertiliser, and the management and utilisation of saline-alkali soils. •Co-inoculation improves the tolerance of alfalfa to saline-alkali environments.•Co-inoculation promotes rhizobia colonisation and nodule formation of alfalfa.•Co-inoculation improves the yield and quality of alfalfa in saline-alkali soil.•Co-inoculation had greater effects than single inoculation.