Abstract: Fruit thining (DF) and retaining fruit (CK) were carried out at different phenological stages of fruit development on one-year-old shoot of Okubo peach trees [Prunus persica (L.) Batsch.] through preventing exportation of the assimilates to the non experimental parts of the tree by girdling one-year-old shoot and keeping the same leaves between fruit thining and CK. The results showed that fruit thining significantly decreased net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but significantly increased leaf surface temperature (TLeaf) at midday as compared with CK. Internal CO2 concentration, soluble sugar content, reductive sugar content, starch content except that at the final fruit rapid growth stage, ADP-glucose pyrophosphorylase and amylase activity in source leaves were not significantly affected by fruit thining. There was a significant positive parabolic correlation between Pn and Gs, and a strong positive linear correlation between Pn and E. Moreover, Pn increased with the increase of TLeaf if TLeaf was lower than 38℃, then decreased sharply when TLeaf exceeded this critical temperature for both fruit thining and CK. Pn of fruit thining was lower than that of CK in the same TLeaf, especially if TLeaf was higher than 38℃. It is suggested that the decreased stomatal aperture and increased leaf temperature may be an important mechanism in regulating photosynthesis under a decreased strength of sink demand by fruit thining in fruit trees.

Key words: Peach, Sink-source relationship, Photosynthesis, Stomatal conductance, Leaf surface temperatur