Characteristics of Photosynthesis in Different Wheat Cultivars under High Light Intensity and High Temperature Stresses

High light associated with high temperature has strong effects on photosynthesis in wheat (Triticum aestivum L.) and results in grain yield loss at maturity. To explore the photosynthetic responses of different wheat cultivars to high light and high temperature (HLHT), we measured the photosynthetic and chlorophyll fluorescence characteristics of flag leaves of four cultivars under the high light intensity of 1 900 μmol m-2 s-1 and high temperature of 35oC. Under natural growth condition (control), both photosynthetic rate under saturated light and saturated light intensity for photosynthesis in Zhengmai 9405 and Zhou 18 were higher than those in Gaocheng 8901 and Yumai 49, and the apparent quantum yield of Zhengmai 9405 was the maximal among the four cultivars. Compared with the control, after the HLHT treatment, the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) in Gaocheng 8901, Yumai 49, and Zhou 18 were significantly reduced, whereas these parameters changed slightly in Zhengmai 9405 with a rather steady Pn value of 11.6 μmol CO2 m-2 s-1 in flag leaves. In the four cultivars, the intercellular CO2 concentration (Ci) showed no significant changes compared with the control, the maximum photochemical effi-ciency (Fv/Fm), the efficiency of open centers of photosystem II (Fv′/Fm′), the actual photochemical efficiency of photosystem II (ФPSII), and the photochemical quenching (qP) decreased while non-photochemical quenching (NPQ) increased significantly, and each of the five chlorophyll fluorescence parameters in Zhengmai 9405 was the highest. The results mentioned above indicated that different cultivars had notable differences in the adaptability to high light intensity and high temperature, Zhengmai 9405 was more adaptable than Gaocheng 8901, Yumai 49, and Zhou 18. The higher Tr and NPQ of Zhengmai 9405 may be one of the rea-sons for its higher photosynthesis rate.