Abstract: The effect of defruiting on source leaf net photosynthesis ( Pn) and related physiological response was investigated on ‘Yanhong’peach trees ( Prunus persica) during the fruit stone hardening and final fruit rap id growth stage. The results showed that Pn, stomatal conductance (Gs) and transp iration ( E)
in source leaves decreased significantly while leaf temperature ( Tleaf ) increased from defruiting trees as compared with those from fruiting ones. There was, however, no significant difference of substomatal CO₂ (Ci)
between fruiting and defruiting treatments. The effect of reducing the sink activity by defruiting treatment on Pn, Gs, E and Tleaf appeared during 9: 00 and 16: 00. The relationship between Pn and Gs was significantly positive only when Gswas less than 60 mmol·m^{- 2} ·s^{- 1}. The difference of Pn between fruiting and defruiting increased with the increasing difference of Tleaf between defruiting and fruiting treatments. It is suggested that an increasing Tleaf , resulting from the stomatal closure, may be a key factorwhich leads the decrease of leaf Pn in reducing the sink activity in fruit trees.

Key words: Peach, Sink-source, Photosynthesis, Leaf temperature