Antioxidant response and biological nitrogen fixation in soybean plants in response to agronomic biofortification with iron

Abstract

Iron (Fe) is an essential element for plants, humans, and animals. The concentration of Fe in the blood is closely related to the concentration of Fe in food, and its deficiency promotes anemia in the human population. In soil, the primary form of Fe is trivalent; however, plants absorb Fe in the bivalent form. The application of high doses of lime increases the pH and makes Fe unavailable in the soil solution for plant absorption. Therefore, strategies such as foliar application of Fe sources and doses are necessary to increase the concentration in plant tissues, providing more physiological stimuli. Fe is involved in various physiological processes in plants, such as chlorophyll formation, photosynthetic processes, antioxidant metabolism (Fe-SOD, CAT, and APX), as well as the formation of leghemoglobin and nitrogenase activity in the nodules of leguminous plants like soybeans. The rate of absorption depends on the Fe source applied to plants (sulfate, nitrate, chloride, and chelate). The objective of this study is to evaluate the antioxidant, photosynthetic responses, and biological nitrogen fixation of soybean plants subjected to three sources and five doses of Fe applied via foliar spray at different phenological stages. The hypothesis of this work is that an optimal concentration of Fe in plant tissues can result in greater protection against oxidative stress by mitigating reactive oxygen species, leading to higher levels of photosynthesis, chlorophyll, and sugars. The higher concentration of sugars and Fe can be translocated via the phloem to the roots, which can influence increased concentrations of leghemoglobin and nodulation. Higher ureide metabolism can promote greater activity of nitrogenous enzymes (nitrate reductase, rubisco), which can increase growth, productivity, and higher Fe concentrations in soybean grains. The higher Fe concentration in grains can enhance Fe availability and potentially improve human health.