Physiological response of winter wheat (Triticum aestivum L.) during vegetative growth to gradual, persistent and intermittent drought

Drought priming at the vegetative growth stage has been demonstrated to be an effective water regulation strategy to enhance drought resistance in wheat. Therefore, exploring the stress response of winter wheat to different soil water changes during this stage can improve the drought priming strategies. This study examined the physiological response of winter wheat during two seasons of greenhouse pot experiments (2018–2019, 2019–2020) in the following four treatments: adequate water supply (control, C), persistent drought (P), intermittent drought (I), and gradual drought (G). An adequate water supply (75–85 % FC, field capacity) was always maintained for treatment C. Before jointing, plants in treatment P were maintained in a drought state (55–65 % FC), while in treatment I, plants underwent a change in soil water status from 55–65% FC to re-watering up to 75–85 % FC and back to 55–65 % FC. After entering the jointing stage, plants in treatments P and I were re-watered to 75–85 % FC. There was no water supplied in treatment G throughout the experiment. The soil water content (SWC) in treatment G gradually decreased with time (100–34 % FC). At the same time, abscisic acid (ABA), and osmotic substances accumulated exponentially with the reduction of SWC, the activity of antioxidant protective enzymes increased significantly, and the change in the stomatal closure rate was faster than the decrease in photosynthetic rate (Pn). Drought priming before jointing in treatments P and I prompted photosynthetic compensation after re-watering at the jointing stage, with the highest Pn in treatment I, followed by treatment P, and lastly, treatment C. The drought-re-watering cycle stimulated the stress response indicators in primed plants; hence, they were significantly higher than the stable levels in non-primed plants. Specifically, the ABA level in the leaves increased faster than the other indicators under repeated drought. Moreover, the relationship between photosynthesis and ABA was stronger than with antioxidative enzymes and osmolytes. Besides, increasing the number of drought-re-watering cycles enabled the primed plants to achieve a higher maximum Pn after re-watering and enhanced the association between soluble sugar and Pn. Overall, increasing the frequency of drought-re-watering enhanced the drought priming effect on the wheat stress response. Besides, there is a time difference in the response of different drought stress indicators to soil water changes. The findings in this study provide an empirical reference for better utilization of drought priming strategies to stimulate crop production.