Mitigation of salt stress by exogenous application of melatonin and its effects on physiological and biochemical aspects in soybean

Abstract

Salinity is an abiotic stress that impairs photosynthesis and plant growth. Melatonin mitigates these effects through its cellular and physiological functions, including improving photosynthetic performance. Soybean, highly important for food security and the economy, requires strategies to reduce these impacts and to clarify its tolerance mechanisms. This research aims to explore the effects of exogenous melatonin application on gas exchange, chlorophyll a fluorescence, and biochemical characteristics of soybean under saline stress conditions. Soybean plants were cultivated in an experimental area of the Federal University of the Semi-Arid Region (UFERSA), Mossoró – RN. The experiment was conducted in a randomized block design arranged in a 3 × 3 factorial scheme (three saline levels in irrigation water – 0.5, 3.0, and 5.0 dS m^-1 and three melatonin concentrations – 0, 0.5, and 1.0 mM), with three repetitions. The saline levels altered gas exchange, chlorophyll a fluorescence, and proline content in soybean plants. Chlorophyll a fluorescence was improved up to the saline level of 3.0 dS m^-1, regardless of melatonin concentration, in soybean plants. The internal CO₂ concentration and the ratio between intercellular and atmospheric CO₂ concentration were mitigated at the saline level of 5.0 dS m^-1 with a melatonin concentration of 0.5 mM.