Effects of heat and high irradiance stress on energy dissipation of photosystem II in low irradiance-adapted peanut leaves

To increase crop yields and not to compete for land with food crops, intercropping agricultural cultivation approach was introduced into cultivation of peanut (Arachis hypogaca L.). This approach improves the total yield of the crop per unit area, but decreases the yield of a single crop compared with mono-cropped agricultural cultivation approach. In wheat-peanut relay intercropping system, peanut plants would suffer heat and high light (HI) stress after wheat harvest. In the present work, peanut seedlings were cultivated in low light to simulate wheat-peanut relay intercropping environments. Upon exposure to heat and HI stress, energy dissipation in PSII complexes was evaluated by comparing those cultivated in low irradiance conditions with the mono-cropped peanut. The maximal photochemical efficiency of PSII (F_v/F_m) and the net photosynthetic rate (P_n) decreased markedly in relay-cropped peanut (RP) after heat and HI stress, accompanied by higher degree of PSII reaction center closure (1–qP). After heat and HI stress, higher antioxidant enzyme activity and less ROS accumulation were observed in mono-cropped peanut (MP) seedlings. Meanwhile, higher content of D1 protein and higher ratio of (A + Z)/(V + A + Z) were also detected in MP plants under such stress. These results implied that heat and HI stress could induce photoinhibition of PSII reaction centers in peanut seedlings and both xanthophyll cycle-dependent thermal energy dissipation and the antioxidant system were down-regulated in RP compared to classical monocropping systems after heat and high irradiance stress.