In this study, we tested whether waterlogging priming at the vegetative stage would mitigate a subsequent waterlogging event at the reproductive stage in soybean [Glycine max (L.) Merr.]. Plants (V3 stage) were subjected to priming for 7 days and then exposed to waterlogging stress for 5 days (R2 stage) with non-primed plants. Roots and leaves were sampled on the fifth day of waterlogging and the second and fifth days of reoxygenation. Overall, priming decreased the H2O2 concentration and lipid peroxidation in roots and leaves during waterlogging and reoxygenation. Priming also decreased the activity of antioxidative enzymes in roots and leaves and increased the foliar concentration of phenols and photosynthetic pigments. Additionally, priming decreased fermentation and alanine aminotransferase activity during waterlogging and reoxygenation. Finally, priming increased the concentration of amino acids, sucrose, and total soluble sugars in roots and leaves during waterlogging and reoxygenation. Thus, primed plants were higher and more productive than non-primed plants. Our study shows that priming alleviates oxidative stress, fermentation, and carbohydrate consumption in parallel to increase the yield of soybean plants exposed to waterlogging and reoxygenation.

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.

Nitrate (NO3-) nutrition is known to mitigate the damages caused by individual stresses of waterlogging and salinity. Here, we investigated the role of NO3- in soybean plants exposed to these stresses in combination. Nodulated soybean cultivated under greenhouse conditions and daily fertilised with a nutrient solution without nitrogen were subjected to the following treatments: Water, NO3-, NaCl, and NaCl + NO3-. Then, plants were exposed to waterlogging (6 days) and drainage (2 days). Compared to plants exposed to isolated stress, the saline waterlogging resulted in higher concentrations of H2O2, O2?-, and lipid peroxidation at the whole-plant level, mainly during drainage. Furthermore, saline waterlogging increased fermentation and the concentrations of Na+ and K+ in roots and leaves both during waterlogging and drainage. NO3- supplementation led to augments in NO3- and NO levels, and stimulated nitrate reductase activity in both organs. In addition, NO3- nutrition alleviated oxidative stress and fermentation besides increasing the K+/Na+ ratio in plants exposed to saline waterlogging. In conclusion, NO3- supplementation is a useful strategy to help soybean plants overcome saline waterlogging stress. These findings are of high relevance for agriculture as soybean is an important commodity and has been cultivated in areas prone to saline waterlogging.