Effects of different canopy layers on leaf photosynthetic characteristics of apple trees

The overall photosynthetic capacity of apple tree canopy is the main factor determining apple tree productivity. Therefore, the effects of different canopy layers on the leaf photosynthetic characteristics of apple trees were studied. From 10-year-old Red Fuji apple orchard, three forms of apple trees named as evacuation stratification apple tree, natural round head apple tree and improved spindle apple tree were selected as the study objectives to measure and compare the seasonal variation of canopy characteristics and leaf quality. The effects of spraying uniconazole (S3307) and Diethylaminoethylhexanoate (DTA-6) on leaf chlorophyll content and net photosynthetic rate of apple trees in different canopy layers were investigated. The difference of light response curves, photosynthetic characteristics, and their correlation to leaves from the surface, middle, and lower canopy layers were studied. The results showed that evacuation stratification form had the best canopy ventilation effect and leaf quality, followed by the improved spindle form. Comparing to the leaf surface sprayed with water (control group), S3307, and DTA-6 treatments increased leaf chlorophyll content and net photosynthetic rate in different canopy layers of apple trees. The net photosynthetic rates of the upper and middle layer leaves treated with plant growth regulator were greatly improved with DTA-6 treatment group higher than that in S3307 treatment group. The leaf photosynthetic rate was much higher in the crown layer than that in the middle and lower layers, which changed obviously with the change of light intensity. The photosynthetic indexes of apple canopy leaves including light saturation rate, stomatal conductance (Gs), intercellular CO2 concentration, transpiration rate (Tr), and photosynthetic nitrogen efficiency were the highest in the surface leaf followed by the middle layer, and then, the lower layer. However, an extremely significant positive correlation was observed between Tr and Gs. Therefore, apple tree productivity can be improved by adjusting the apple tree canopy to increase the leaf photosynthetic capacity. © (2023). All Rights Reserved.