Stress Response Of Photosynthetic And Chlorophyll Fluorescence Characteristics Of Taxus Cuspidata Seedlings Under Different Light Conditions

In order to know the characteristics of light adaptation of Taxus cuspidata for the efficient cultivation,5-years seedlings were selected to study the diurnal changes of photosynthetic and chlorophyll fluorescence characteristics under 3 different light conditions(FL:full light; F1: 60% FL; F2:30% FL), reveal the physiological characteristic response to the change of temperature and light. The results were as follows:The photosynthetic rate (Pn) of all 3 groups had a double-peak curve. The Pn values of seedlings at 9:00 were higher than that of Pn at 15:00 significantly in summer, the Pn values under F2 light condition were the highest, and the Pn values under the F1 light condition were higher than that of FL. The Pn values under FL light condition were the highest in autumn, and the Pn values under F2 condition were higher than that of F1. The highest Pn values under F2 and Fl conditions in summer were higher than that in autumn, but the highest Pn values under FL condition were just the opposite. The changes of stomatal conductance (Gs) and transpiration rate (Tr) showed a similar pattern of the Pn values (double-peak), they reached the maximum values at the same time. The intercellular carbon dioxide concentration (Ci) showed a "V" curve trend, the change trend of the limitation of stomatal (Ls) was opposite with the Ci, showed a monopeak curve. The Ci values reached the maximum while Ls reduced to the minimum at 11:00 in autumn. The values of water use efficiency (WUE) under Fl and F2 were higher than the values under FL in summer, but in autumn the values under FL were the highest.The efficiency of solar energy conversion (Fv/Fm) and the potential activity of PSII (Fv/Fo) of 3 group seedlings reduced to the lowest and then rised, the values under Fl and F2 conditions were higher than that of FL condition.The Fv/F0 values were more sensitive than Fv/Fm to the change of light. Quantum yields of photosystem Ⅱ(ΦPSⅡ) under the conditions of F1 and F2 maintain a higher level in a day. The ΦPSⅡ values under FL were the lowest, the differences between 3 groups were relatively small in the morning, but in the afternoon the difference increased. The recovery time of ΦPSⅡ in autumn was earlier than that in summer. At first, the quenching coefficient (qP) variation of three groups rised slowly, and then reduced in different levels with the increase of light intensity and temperature. In summer, the daily mean values of qP under the condition of F2 were the highest, the values under FL were the highest in autumn. In summer, the daily values of non-photochemical quenching rate (NPQ) under F2 condition reduced slowly in a day, the values under FL and F1 reached the maximum at 9:00 and 13:00 (15:00), in autumn, the values under FL and F1 conditions rised in the morning, then reduced lower than that under F2 conditions, and remain a low level.