Responses of photosynthetic fluorescence characteristics, pollination, and yield components of maize cultivars to high temperature during flowering

High temperatures during the flowering stage are likely to have a significant negative impact on maize growth and development, which is one of the most important factors affecting maize high and stable yield. This study aimed to evaluate the response of photosynthetic fluorescence characteristics, pollination, and yield components of different maize cultivars to high temperatures during the flowering stage to provide a theoretical basis for the stable and high yield of summer maize production under climate warming in the future. This study used heat-resistant maize cultivars, ‘XD20’ and ‘ZD958’, and heat-sensitive maize cultivars, ‘XY335’ and ‘NH101’, as research materials in a greenhouse. Then the influence of high temperature during the flowering stage (from 7 d before silking to 7 d after silking) on grain yield, leaf photosynthetic fluorescence characteristics, pollination, dry matter mass were investigated. High temperature during flowering significantly reduced the kernel number per ear and significantly increased the blank stem rate of different summer maize cultivars, leading to a significant decrease in grain yield. The grain yield decline of heat-resistant cultivars was less than that of heat-sensitive cultivars. Compared with the control, the kernel number per ear of the heat-resistant and heat-sensitive cultivars under high temperature significantly decreased by 22.25% and 67.18%, respectively, the 100-grain weight decreased by 2.03% and 5.00%, the blank stem rate significantly increased by 206.37% and 283.00%, and the grain yield significantly decreased by 31.84% and 67.33%, respectively. High temperature during flowering reduced effective green leaf area and chlorophyll content, impaired photosystem II, and significantly decreased the photosynthetic performance of the four maize cultivars. Under high-temperature stress, the leaf area of the heat-resistant and heat-sensitive cultivars decreased by 0.79% and 7.46%, the chlorophyll content decreased by 4.53% and 5.16%, the net photosynthetic rate (P_n) decreased by 19.9% and 31.6%, and the maximum photochemical efficiency (F_v/F_m) of PS Ⅱ decreased by 0.79% and 1.47%, respectively. After the high-temperature stress, some parameters of photosystem Ⅱ recovered, and chlorophyll content and P_n returned to the control level. High temperatures during flowering had little effect on the tassel branch number, tassel floret number, and ear filament number; but shortened the pollen shedding duration, lengthened the anthesis-silking interval, and significantly reduced the setting rate. Under high-temperature stress at the flowering stage, the tassel branch number of heat-resistant and heat-sensitive cultivars decreased by 4.76% and 13.66%, the tassel floret number decreased by 8.53% and 8.32%, the tear filament number decreased by 6.10% and 7.17%, the pollen shedding duration decreased by 10.81% and 26.94%, the anthesis-silking interval increased by 58.93% and 85.00%, the pollination duration decreased by 17.91% and 58.95%, and the kernel setting rate decreased by 14.77% and 63.10%, respectively. Shortening pollination duration was the main reason for the lower kernel setting rate. High temperature during flowering significantly reduced dry matter mass and the distribution ratio of dry matter to the ear or grain of four maize cultivars. After high-temperature stress, the dry matter mass per plant of heat-resistant and heat-sensitive cultivars decreased by 13.7% and 17.6%, and the distribution ratio of dry matter in the ear decreased by 49.16% and 56.51%, respectively; at maturity, the dry matter mass per plant decreased by 16.40% and 25.73%, and the distribution ratio of dry matter in the grain decreased by 7.08% and 46.80%, respectively. High temperature during flowering decreased the photosynthetic performance, inhibited the coordinated development of male and female panicles, and significantly reduced kernel setting rate, kernel number per ear, and grain yield. Compared with heat-sensitive cultivars, heat-resistant cultivars had higher photosynthetic capacity and pollination fruiting ability under high-temperature stress; their yield was less affected by high temperature.