High temperature effects on maize photosynthesis during stress and recovery phase at the seed setting stage.

With the climate change, high temperature (HT) stress will have more serious impacts on maize production. Photosynthesis is the basis of maize yield, which is also sensitive to HT. HT effects are not only occurred during the stress periods, but also lasted after the stress is removed, but with few attention. To explore the maize photosynthesis after HT removal, two maize varieties with different heat sensitivity (Jinhai 5 (JH) in 2021; JH and Xianyu 335 (XY) in 2022) were exposed to HT using the pot experiment in environment-controlled greenhouses. Photosynthesis and relevant physiological parameters were measured during stress periods and at the recovery phase. Results showed that at the ending of HT, maize photosynthesis were all significantly inhibited of the two maize varieties in the two years. At the recovery phase, photosynthesis of JH was not recovery at 2 d and 3 d after HT removal in 2021 and 2022, which was 23.8% and 14.7% lower than control. For XY, the photosynthesis was 11.2% lower than control at 5 d after HT removal in 2022. Chlorophyll fluorescence parameters were significantly changed during HT periods. The lasting effects on chlorophyll fluorescence were not showed in JH, but occurred in XY. Malondialdehyde (MDA), peroxidase (POD) and superoxide dismutase (SOD) increased by 49.5%, 21.6% and 36.8% under HT, and accumulation were also found at the 2 d after HT removal, with much higher for POD and SOD (38.3% and 40.1%). Meanwhile, the arrangement and morphology of chloroplasts in mesophyll cells significantly changed, and even could not recover at 4 d after HT removal. Finally, HT stress caused significant yield penalty on maize.