Effect of shading treatment on photosynthetic characteristics and flower quality of Paeonia suffruticosa.

The effects of different shading treatments(100%,65%,45% and 15% of full sunlight) on the photosynthetic characteristics were examined with five cultivars of Paeonia suffruticosa during the period from 2008 to 2011.The results indicated that the light-saturation point(LSP) and the light-compensation point(LCP) of the five cultivars of P.suffruticosa under the full sunlight were quite high.LSPs were about 1 000 μmol·m-2·s-1 and LCPs were 73～100 μmol·m-2·s-1.With the sunlight intensity reducing,the LSPs and LCPs of all cultivars decreased gradually.The net photosynthetic rates(Pn) under 65% sunlight were significantly higher than those under full sunlight.Under 45% sunlight the Pn of 'Aoyang' and 'Zhuguangmorun' were significantly higher than those under full sunlight,while the Pn of other three cultivars had no remarkable change.The Pn of all the cultivars under 15% sunlight were significantly lower than those under full sunlight.The flowering rates of all the cultivars were quite high under 65% and 45% sunlight and there were no difference with those under full sunlight.But under 15% sunlight they were significantly lower than those under full sunlight.The flower diameters of all the cultivars under 65% sunlight were increased and those under 15% sunlight were decreased significantly.Under 45% sunlight the flower diameters were increased at different levels except 'Aoyang'.The effects of different shading treatments on the flower color were related to the sunlight intensity and the color of the flower itself.The color of all the cultivars had no remarkable change under 65% sunlight and they even got improved for 'Fenzhongguan' and 'Yingrihong',but they both gradually become lighter under 45% and 15% sunlight.With the same trend the color of 'Zhuguangmorun' became gradually lighter and blue.The color of 'Aoyang' under 45% had no change with those under full sunlight,but become lighter under 15% sunlight.For 'Lanbaoshi' it had no remarkably change under different shading treatments.It is indicated that P.suffruticosa is a sun plant with shade tolerance.Moderate shading can improve its photosynthesis and the flower quality but strong shading makes them worse.