Abstract: Effects of different light intensity on chlorophyll fluorescence and the level of D1 protein in threeyearold sweet cherry (Prunus avium L.) variety Xianfeng grafted on P. mahaleb L. were investigated. The accumulation of H2O2 in leaves treated with NaHSO3 and exogenous ROS scavenger ascorbic acid (AsA) was also studied. The results showed that maximal photochemical efficiency of PSⅡ (Fv/Fm), electron transport rate (ETR), quantum yield of PSⅡ (ΦPSⅡ), nonphotochemical quenching (NPQ) declined, while initial fluorescence (Fo), photochemical quenching (qP) and the relative content of D1 protein had no obvious changes in leaves under 1 800 μmol·m-2·s-1 radiation for 6 h. Compared with the control (H2O), leaves treated with 5 mmol·L-1 NaHSO3 and 4 mmol·L-1 AsA had a less decline in Fv/Fm. These results indicated that the reduction in Fv/Fm was not a damage to the photosynthetic apparatus but a photoprotective strategy by downregulating of photosynthetic function in sweet berry under high light, and low concentrations of NaHSO3 and AsA solution could protect the PS Ⅱ against photodamage in cherry leaves．

Key words: sweet berry, chlorophyll fluorescence, D1 protein, high light, H2O2