Increased soybean tolerance to high-temperature through biostimulant based on Ascophyllum nodosum (L.) seaweed extract

Heat stress is one of the environmental factors that most limits soybean productivity (Glycine max (L.) Merrill). The use of biostimulants based on Ascophyllum nodosum (L.) Le Jolis seaweed extract can mitigate the effects of heat stress. Therefore, the effects on the morphological, physiological, biochemical and productive variables of soybean grown at high temperature and under exogenous application of a biostimulant based on seaweed extract were investigated in this research. The results showed that the application of 1 L ha(-1) biostimulant based on seaweed extract increased the tolerance of soybean plants to heat stress, as it increased the rate of CO2 assimilation, stomatal conductance, the rate of transpiration and carboxylation efficiency, in addition to reducing leaf temperature, but did not influence the efficiency of water use and relative chlorophyll content (SPAD index). In addition, the application of the biostimulant based on seaweed extract increased the activity of the antioxidant enzymes superoxide dismutase, catalase and ascorbate peroxidase; and maintained the activity of peroxidase and reductase nitrate, as well as the proline concentration. Furthermore, the foliar application of the biostimulant based on A. nodosum extract improved the biometric and production characteristics, resulting in greater productivity. Based on these beneficial properties, the biostimulant based on algae extracts at a dose of 1 L ha(-1) proved to be effective in alleviating the adverse effects of heat stress in soybeans.