Abstract: The present study was carried out to investigate the effects of high temperature on photosynthetic fluorescence characteristics and antioxidant enzyme activities in maize ear leaves. The pot experiments were carried out at Fengyang Experimental Station of Anhui Science and Technology University June to October 2021. Two maize cultivars, "Anke 985" and "Longping 206", were chosen in this study. The average temperature of high temperature treatment was (37±2)°C during the daytime, and the high temperature duration was 30 days. The indices including contents of yield, chlorophyll relative content (SPAD), photosynthetic parameters, chlorophyll fluorescence parameters, antioxidant enzyme (CAT, SOD, POD) activity and malondialdehyde (MDA) content of maize were measured under different treatments. The results showed that compared with the control, high temperature treatment reduced significantly grain number per row, 100-grain weight, thereby reducing maize yield per plant. The chlorophyll relative content (SPAD), net photosynthetic rate (Pn) and stomatal conductance (Gs) of maize leaves significantly decreased under high temperature treatment, while intercellular carbon dioxide concentration (Ci) increased significantly, indicating that the decreased of net photosynthetic rate (Pn) was mainly affected by non-stomatal factors. High temperature treatment had significant effect on fluorescence parameters of maize. The maximum photochemical efficiency Fv/Fm, actual photochemical efficiency (ΦPSII) and photochemical quenching (qP) of maize ear leaves decreased significantly, but the non-photochemical quenching (qN) increased significantly under high temperature treatment. After high temperature treatment, the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in maize significantly decreased, but the malondialdehyde (MDA) content increased significantly. In conclusion, high temperature treatment damaged the photosynthetic apparatus of maize leaves, the activity of antioxidant enzymes decreased, the degree of membrane peroxidation increased, the relative content of chlorophyll decreased, and inhibited the photosynthetic performance, which led to the accumulation of photosynthetic assimilates blocked, resulting the maize yield decreased significant.

Key words: Maize, High temperature, Photosynthetic characteristics, Chlorophyll fluorescence, Antioxidant enzyme, Yield