Supplemental irrigation mitigates yield loss of maize through reducing canopy temperature under heat stress

Due to global warming, high temperature stress severely impacts maize growth and development, especially during the early filling stage. Supplemental irrigation is an effective measure to mitigate high temperature stress in maize. However, the underlying mechanism for alleviating transient high temperature stress during the early grain-filling stage is still unclear. A two-year field experiment involving high temperature during the early filling stage (HT), supplemental irrigation under high temperature stress (HTW), supplemental irrigation under control condition (W), and control treatment (CK) by using heat-tolerant variety ZD958 and heat-sensitive variety XY335 was conducted. Compared with the CK treatment, the HT treatment significantly decreased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). HT also significantly reduced the Pn, soluble sugar content in stem, and dry matter accumulation, thus reducing kernel number per ear and yield by 11.2–17.6% and 23.4–23.7% in the both variety, respectively. However, compared with HT, the HTW treatment reduced the daily mean canopy temperature of ZD958 and XY335 by 2.6 °C and 2.8 °C, respectively. Accordingly, HTW increased SPAD value, photosynthetic performance, starch and soluble sugars content in stems and leaves, and antioxidant enzymes activities, but reduced the malondialdehyde (MDA). Moreover, HTW increased the grain sink capacity, prolonged the effective filling days by 1.4–6.5 d, and increased the average filling rate by 14.8–41.0% compared with HT. Finally, grain yield of HTW was increased by 15.8–22.3% compared with HT. Therefore, supplemental irrigation could effectively enhanced maize heat resistance by reduce canopy temperature. This study provides important insights into enhancing maize resistance and yield stability under a warming climate.