High Daytime and High Nighttime Temperatures Affect the Leaf Photosynthetic Characteristics of Waxy Maize (Zea mays L. var. ceratina Kulesh) During Grain Formation

Day and night high temperatures (HT) has become an inevitable environmental factor in maize production. However, few studies have compared the differences in photosynthetic characteristics of leaves and yield formation during grain filling under daytime HT (DH) and nighttime HT (NH). This study utilised waxy maize and a temperature-controlled pot experiment to assess the impacts of DH, NH and the combination of DH and NH (DNH) treatments at the early filling stage. Compared to the control, three HT treatments resulted in the decrease of grain weight and volume at the middle and late filling stage, and the degree of influence was DNH > DH > NH. During the grain-filling process, DNH and DH treatments reduced the leaf water content, disturbed protein biosynthesis and antioxidant system, accelerated chlorophyll hydrolysis, inhibited phosphoenolpyruvate carboxylase and Ribulose-1,5-bisphosphate carboxylase activities, and reduced post-silking dry matter accumulation and translocation. DNH and DH treatments affected leaf photosynthetic efficiency by changing the gas exchange parameters and PSII reaction, which in turn influenced the maximum photochemical efficiency, electron transport rate, and energy conversion. However, NH treatment only affected some stages of grain filling and had less effect on protein synthesis and antioxidant enzyme activity than DH and DNH. These new findings complement the comparison between DNH in photosynthetic characteristics and yield of waxy maize.