Physiological mechanisms of cross-stress and memory in soybean plants subjected to water deficit and waterlogging

Defense priming is a strategy that enables plants to react faster, minimizing the damage suffered and allowing them to survive stress. Here, we investigated the physiological and morphological changes underpinning stress memory and adaptive capacity in soybean plants subjected to water deficit and/or waterlogging at two developmental stages. Our experiment was carried out in a greenhouse with seven treatments and four replicates: water deficit at R2; water deficit both at V4 and R2; water deficit in V4 and waterlogging in R2; waterlogging in R2; waterlogging in both V4 and R2; waterlogging at V4 and water deficit at R2, and control (non-stressed plants). Samples for biometric analyses, measurements of xylem water potential, leaf gas exchange, chlorophyll a fluorescence, and quantification of photosynthetic pigments were harvested on the last day of stress (R2) and four days after recovery. Primed and cross-primed plants showed improvements in leaf water potential and relative water content due to the maintenance of stomatal opening and greater water use efficiency. Together with the osmotic effects, these plants developed greater protection of the photosynthetic apparatus, showing a superior capacity to transfer energy between photosystems as well as to dissipate photon excess as heat. They also showed a greater ability to recover after periods of stress and maintained carotenoid levels. This study adds another piece of evidence that soybean plants have stress memory, important to maintain productivity under a changing climate.