Effects of Fruit Removal,Shoot Girdling and New Shoot Bagging on Leaf Soluble Sugar Content and Photosynthesis of Peach Leaves

In 'Lvhua 9' peach(Prunus persica(L.) Batch) trees,a series of source leaves with differing levels of soluble sugar content were created by retaining fruit("+fruit"),removing fruit("-fruit") or reducing the light period.To alter the light period,leaves were covered with a bag made of brown inner paper and outer silver paper,which was then removed at different times the next day.The highest level of leaf soluble sugar content was obtained by fruit removal,while reducing the light period resulted in a lower level than "+fruit".The results showed that,net photosynthetic rate(Pn) and stomatal conductance(Gs) decreased,but leaf temperatures(tleaf) increased,following an increase in soluble sugar content levels in leaves.After the "-fruit" treatment,reduced Pn was correlated with lower Gs,and tleaf increase was concomitant with decreases in maximal quantum yield of photosystem Ⅱ(Fv/Fm),actual photochemical efficiency of photosystem Ⅱ(ΦPSⅡ),and photochemical quenching,and with an increase in non-photochemical quenching(NPQ).Therefore,instead of feedback regulation by the accumulation of end products in source leaves,a high tleaf induced by decreased stomatal aperture may play a key role in regulation of photosynthesis by limiting the photochemical efficiency of the PSⅡ reaction centers under high levels of the soluble sugar content in peach leaves.