Response of photosynthetic and fluorescence characteristics of Japanese yew seedlings to different light conditions.

Four-year-old Japanese yew seedlings were taken as experimental materials to study the photosynthetic and chlorophyll fluorescence characteristics under four light conditions, i. e. FL: full light; L1: 50% FL; L2: 30% FL; L3: 15% FL. The results showed that the contents of chlorophyll a, chlorophyll b and total chlorophyll under L2 condition were the highest, FL declined the contents of chlorophyll a, chlorophyll b and total chlorophyll significantly; the lowest value of chlorophyll a/ b was 2.203 when appeared under L3 condition, and it was significantly lower than the normal range. The trends of light response curve of photosynthesis of Japanese yew seedlings were basically consistent under three shade conditions, the net photosynthetic rate (Pn ) increased rapidly and then slow down follow photosynthetically active radiation(PAR)enhanced, and Pn under L2 condition was the highest, then was under L3, that under L1 was the lowest; Pn under FL condition declined obviously when PAR 1 000 μmol/ (m2·s). The maximum net photosynthetic rate (Pmax ), average net photosynthetic rate (Pa ), light saturation point (LSP), apparent quantum yield (AQY) and the stomatal conductance (Gs) under L2 condition were the highest, while the light compensation (LCP) and the dark respiration Rd were relatively low. LSP and AQY under FL condition were the lowest, while LCP and Rd were the highest. Compared with shade conditions, the fluorescence parameters basis fluorescence (F0) under FL seedlings rose significantly, the maximum fluorescence (Fm ), variable fluorescence (Fv ), potential activity of PSⅡ(Fv / F0 ) and the efficiency of solar energy conversion (Fv / Fm ) reduced obviously, the non- photochemical quenching coefficient (qN) rose slightly, photochemical quenching coefficient (qP) and the electron transport rate ( ETR) reduced slightly. The fluorescence parameters under L2 and L3 conditions had little difference. The fluorescence parameters appeared that the seedlings under L2 and L3 conditions were more suitable than those under L1 condition. All these results indicate that the photosynthetic mechanism of Japanese yew seedlings is destroyed under full light, and about 30% of full light condition was most suitable.