Studies On The Mechanisms Of Low-light-tolerance Of Peach Tree In Protected Culture

Based on the protected culture practice of peach trees in north China ,the research had been carried out in the demonstration of college of horticultural science and engineering of Agricultural University with two-year-old"Chunjie"peach( Prunus persica L. cv. chunjie)/"Dongxuemitao"(Prunus persica (L.)Batsch)) from the year 2004 to 2005.The effects of low irradiance on the characteristics of photosynthesis,characteristics of chlorophyll fluorescence,metabolism of active oxygen species and membrane lipid peroxidation of leaves in greenhouse,photoinhibition and recovery of leaves which were under low irradiance after the covers were removed. The main results were as follows:1,Net photosynthesis and the concerned parameters changed extremely with the reduction of photon flux density. The light compensation point (LCP) and light saturation point(LSP) of leaves in 10.5% photic rate reached 18.26μmol.m-2.S-1,245.53μmol.m-2.S-1 ,which was 61.4% and 48.6%of 100% photic rate (29.75μmol.m-2.S-1, 505.43μmol.m-2.S-1); otherwise, The CO2 saturation point (CCP) and CO2 compensation point(CSP) of leaves in 10.5% photic rate reached 47.46μmol.mol-1,477.32μmol.mol-1 ,which was only 66.1 % and 44.1 % of 100% photic rate (71.75μmol.mol-1,1083.32μmol.mol-1). Rubisco activity expressed the trend of reduction under low irradiance. The content of photosynthesis pigments (Chlorophyll a,Chlorophyll b,carotenoids) increased with the reduction of irradiance ,but the content of the three kinds of pigments reduced in the later time of protected culture . The diurnal change of net photosynthesis expressed three-apex-curve, which the maximal value was at 10 o'clock.All the parameters above reached the level of significance of difference between all the treatments(P=0.05).2,The chlorophyll fluorescence(φPSⅡ,Fv/Fm) of two low irradiance treatment changed little . But the use of chlorophyll fluorescence played an important role in proving the photoinhibition of peach trees. The chlorophyll fluorescence(φPSⅡ,Fv/Fm) changed sharply after the removed of the covers , the values which changed from 0.741and 0.83 to 0.698 and 0.229 could not...