Effects of Different Calcium Salts on Photosynthetic Characteristics of Malus baccata Borkh. under Changing Temperature

In order to study the effects of calcium salts (2%CaCl2 and 1%CaAc2, w/v) on the photosynthetic characteristics of apple leaves under dramatically changing temperature (5 degrees C -> 420 degrees C -> 10 degrees C -> 40 degrees C), seedlings of Malus baccata Borkh. were used as materials in this experiment by using plant efficiency analyzer. The results showed that, compared with the control, calcium treatments significantly decreased the relative variable fluorescence at the K-step (Wk), relative variable fluorescence at the J-step (Vi), however, maximum quantum efficiency of PSII (F-v/F-m) were at a higher level, indicating a alleviating effect of 2%CaCl(2)and 1%CaAc2 treatments on PSII light inhibition. Meanwhile, in the cooling phase, 2%CaCl2 and 1%CaAc2 treatments improved RuBPase activities and decreased MDA contents, further explaining the positive role of calcium salts treatments in regulating PSII photosynthetic apparatus under temperature stress, in addition, the alleviating effect of 1%CaAc2 treatment is better than that of 2%CaCl2 treatment.