Abstract:

By comparing the differences of photosynthetic characteristics, net photosynthesis rate (P_n), intercellular CO₂ concentration (C_i), stomatal conductance (G_s), transpiration rate (T_r) and light photo response curve were determined in four Malus sp. (Pink spire, Ruby, Kelsey, Radiant) . The results showed that Kelsey presented single curve in the diunal variation of P_n, while the others were double curve. Diurnal variation of C_i showed as “V” shape, which was high in the morning and evening but low at noon. Diurnal variation of G_s presented single and double curves, and diurnal variation of T_r presented single curves, the highest value appeared at 10:00-14:00. Diurnal variation of WUE presented multiple types. But they were high in the morning and low in the evening. The maximum net photosynthetic rate, light saturation point and surface photon quantum efficiency of Kelsey were the highest, the compensation point of light was the lowest, and the dark respiration rate of Ruby was the lowest. The average net photosynthetic rate of the four cultivars was as follows: Kelsey (8.33 μmol·m^-2·s^-1)>Radiant (7.71 μmol·m^-2·s^-1)>Pink spire (7.29 μmol·m^-2·s^-1)>Ruby (5.57 μmol·m^-2·s^-1). Photosynthetic capacity of Kelsey was the highest, and could be planted with low light requirements. The photosynthetic capacity of Ruby was the weakest and showed weaker adaptability to light environment, which can be used as a new variety for pot culture. Pink spire was photophilic, and should be planted in areas with sufficient light. Pink spire had a certain adaptability to low light intensity, which can be mixed with other tree species in garden application with weak light.

Key words: Malus sp., photosynthetic characteristics, diurnal variation, light responses curve