Adubação suplementar com enxofre como atenuador dos efeitos do estresse salino em plantas de alface hidropônica

Abstract

Lettuce is one of the most grown vegetables in Brazil, spreading practically throughout the national territory, including in the semi-arid regions of the Northeast, where the availability of good quality water is increasingly scarce. Therefore, it is important for the horticultural sectors to develop research and techniques that allow the cultivation of plants using saline water. Thus, this study aimed to evaluate the effects of leaf fertilization with sulfur in lettuce plants grown under hydroponic system and under salt stress. The experiment was conducted in a 2 x 3 factorial arrangement, with the plants submitted to two levels of salinity in the nutrient solution (0 and 40 mM of NaCl) and at three levels of supplemental fertilization with sulfur (0.0, 1.5 and 3.0 g L-1), with four replicates. Physiological and biochemical characteristics and mineral nutrition of shoots were analyzed. The growth, photosynthesis and stomatal conductance of plants were reduced by salt stress. However, those plants supplemented with sulfur fertilizer treatment this reduction was attenuated. Under natural conditions of cultivation, treatment with sulfur at 1.5 g L-1 also resulted in better growth and plants development. The salt stress increased the Na +/K+ ratio in leaves of lettuce plants, but this was less pronounced in those supplemented with sulfur. In plants under salt stress, membrane damage was lower in those fertilized with sulfur, which also presented lower levels of hydrogen peroxide, higher activity of antioxidant enzymes, such as ascorbate peroxidase and catalase. In general, the nutrient solution salinity reduced the nutrient uptake, but for potassium and phosphorus this reduction was minimized by the supplemental sulfur. It is concluded that supplemental fertilization with sulfur attenuated the deleterious effects of salinity on the growth and gas exchange of lettuce plants, and that this, at least in part, was due to a more efficient antioxidative system, associated with a better phosphorus and potassium uptake and a lower Na+/K+ ratio.