High night temperature during the effective grain-filling stage affects maize yield and quality

Global warming has led to a disproportionate increase in night temperature, imposing additional constraints on crop growth and yield. However, how maize (Zea mays L.) responds to high night temperature (HNT) during the effective grain-filling stage remains unclear. This study aimed to determine how HNT affects maize yield, grain quality, photosynthesis-respiration coordination, and starch metabolism. A temperature-controlled experiment with heat-sensitive hybrid (ZY 309) and tolerant hybrid (JH 5) was carried out. Night temperature treatments of 24 °C (control), 26 °C, 28 °C and 30 °C were applied for 18 consecutive days encompassing the effective grain-filling stage. The grain yield of ZY 309 decreased significantly by 9.27% and 13.64% at 28 °C and 30 °C, and that of JH 5 decreased significantly by 11.19% at 30 °C. At 30 °C, grain starch content decreased by 2.27% in ZY 309 and 2.70% in JH 5, lipid content decreased by 11.37% and 10.61%, respectively, whereas protein content increased by 11.46% and 9.92%, and coarse fiber content increased by 10.56% and 5.30%. Although leaf photosynthesis of ZY 309 remained 27.19% and 39.00% higher than the control at 28 °C and 30 °C, this increase did not prevent yield loss. Night respiration increased with temperature and treatment duration, with a stronger response in ZY 309. The expression levels of AM-AGPase SS and AM-AGPase LS were more significantly reduced in ZY 309 than JH 5. These results indicate that HNT during effective grain filling reduces maize yield and grain quality, mainly by increasing respiratory carbon cost and weakening starch biosynthesis, with ZY 309 showing greater sensitivity than JH 5.