Co-inoculation of Seeds with Bradyrhizobium,Azospirillum, andRhizophagusImproves Nitrogen Assimilation and Growth in Soybean Plants Subjected to Waterlogging

Plant growth-promoting bacteria and arbuscular mycorrhizal fungi improve plant tolerance to abiotic stress. Here, we evaluated the growth and nitrogen metabolism parameters of soybean (Glycine max (L.) Merril) plants subjected to waterlogging, followed by reoxygenation. Seeds were inoculated with Bradyrhizobium or co-inoculated with Bradyrhizobium and Azospirillum brasilense and/or Rhizophagus intraradices. Plants were subjected to waterlogging at the V8 stage for eight days, followed by reoxygenation for an additional four days. After both periods, plants were collected for growth analyses and quantification of amino acid and ureide content and glutamine synthetase (GS) and glutamate synthase (NADH-GOGAT) activity. Plants co-inoculated with A. brasilense and R. intraradices had increased levels of amino acids and ureides when exposed to waterlogging and reoxygenation. Similarly, co-inoculation increased GS and NADH-GOGAT activity during both conditions and mitigated the decreases in plant growth caused by waterlogging. Our results indicate that co-inoculation with Bradyrhizobium, A. brasilense, and R. intraradices alleviates the nitrogen deficit and improves the biomass accumulation of soybean plants exposed to waterlogging stress. However, A. brasilense showed the best performance in dealing with waterlogging conditions and recovering from them.