Effects of Shading on Growth and Photosynthetic Characteristics of Rosa hybrida

The effects of different shading treatments(25%,50%,75% and 100% of full sunlight)on the growth,photosynthetic characteristics and chlorophyll fluorescence parameters of Rosahybridawere examined in order to know the growth and physiological responses of R.hybridato light regimes.(1)It has been found that with the decreasing light intensity,the leaf thickness,and flower diameter and flower formation rate decreased,while the Chl content increased.The net photosynthetic rate(Pn),transpiration rate(Tr), stomatal conductance(Gs)and intercellular CO2 concentration(Ci)all decreased with the decreasing of light intensity,while the stomatal limitation value(Ls)increased.(2)The light compensation point(LCP),light saturation point(LSP)and dark respiration rate(Rd)also decreased as a mechanism of physiological adaptability to light decreasing.The adaptability of R.hybridato light was wide because the LSP was 600~1 200μmol·m-2·s-1 and the LCPwas 29.89~62.95μmol·m-2·s-1.The CO2 compensation point(CCP)was 78.16~89.41μmol·mol-1,the CO2 saturation point(CSP)was about 1 100μmol· mol-1 and the potential maximum photosynthetic capacity(Pm)was 13.06~25.63μmol·m-2·s-1, which indicated that light intensity and CO2 concentration have greater impact on photosynthesis rate.(3)The chlorophyll fluorescence parameters indicated that with the increasing of light stress,the reaction center of PSⅡ was destroyed,photosynthetic electron transform capability was weakened and photosynthesis was restrained.It is indicated that R.hybridais a sun plant with shade tolerance.Moderate shading(75% of full sunlight)can improve its photosynthetic capacity and the flower quality,and reduce the photoinhibition in R.hybrida.