RESUMO
Iron toxicity is a major challenge faced by plants in hypoxic soils; however, the consequences of such combined stress for soybean (Glycine max) remain to be determined. Here we assessed the physiological responses of soybean plants exposed to hypoxia and a high concentration of iron. Soil-grown plants cultivated in a greenhouse until the vegetative stage were transferred to a hydroponic system containing nutrient solution and subjected to two oxygen conditions (normoxia (6.2 mg L-1) and hypoxia (0.33 mg L-1)) and two iron concentrations (Fe-EDTA) (0.09 and 1.8 mM) for 72 h. During hypoxia, high concentrations of iron in the nutrient solution resulted in increased iron accumulation in roots and leaves. Under this condition, the concentrations of zinc, nitrogen, potassium, and calcium decreased in the roots, while the concentration of nitrogen and magnesium decreased in the leaves. Additionally, during hypoxia, the higher concentration of iron led to an increase in the activity of the antioxidant enzymes in roots and leaves, while decreased the levels of the photosynthetic pigments, leaf gas exchange, and plant growth. In conclusion, high iron concentration in the root medium results in a considerably more severe damage condition to soybean plants under hypoxia compared to plants grown under low iron availability.