The Physiological Mechanism of Coupled Regulation Between Water Deficit Severity and Deficit Period on Winter Wheat Yield

Regulated deficit irrigation is a vital method for developing water-saving agriculture. The degree of and the period of water deficit are two key factors determining the effectiveness of regulated deficit irrigation. In this study, winter wheat was used as the experimental material, and water deficit was imposed by reducing the irrigation lower limit. Three water deficit treatments were established, with irrigation lower limits set at 65%, 55%, and 45% of field capacity, respectively. There were three stages of water deficit: the jointing stage, the heading-anthesis stage, and the ripening stage; full irrigation (with a minimum irrigation level of 75% field capacity) served as the control. The physiological and growth indicators were measured, including plant water status, osmotic regulation, antioxidant activity, leaf gas exchange and yield. The variation patterns of physiological indicators during the irrigation cycle under reduced irrigation lower limits at different growth stages were explored. The synergistic response relationships among physiological indicators were analyzed; the physiological mechanism by which the degree and stage of water deficit jointly influence winter wheat yield was elucidated. The results indicate that lowering the lower limit of irrigation reduces net photosynthesis prior to irrigation. When the lower irrigation threshold exceeds 55%, chlorophyll content remains largely unaffected. However, increased stomatal conductance following irrigation results in higher net photosynthesis under the low irrigation threshold treatment compared to the control. When the irrigation lower limit is below 55%, chlorophyll content decreases significantly, resulting in net photosynthesis remaining markedly lower than the control even after irrigation. During the jointing stage and heading-anthesis stage, plants exhibit weaker osmotic regulation and antioxidant capacity, and the chlorophyll content is greatly affected by water deficit, resulting in reduced net photosynthesis before and after irrigation, leading to a greater decrease in winter wheat yield. The results on the physiological and biochemical characters (excluding gas exchange parameters) are limited to one year. The research findings provide the theoretical reference for regulated deficit irrigation of winter wheat.