A Study on Photosynthetic Physiological Characteristics of Six Rare and Endangered Species

The parameters of gas exchange and chlorophyll fluorescence in leaves of six rare and endangered species Neolitsea sericea, Cinnamomum japonicum var.chenii, Sinojackia microcarpa, Discocleidion glabrum var. trichocarpum, Parrotia subaequalis, Cercidiphyllum japonicum were measured in fields. The results showed that there were significant differences in photosynthetic capacity, intrinsic water use efficiency(WUEi), the efficiency of primary conversion of light energy of PSⅡ and its potential activity, the quantum yield of PSⅡ electron transport, and the potential capacity of heat dissipation among the six species. However, there was no significant difference in WUE. The highest values of net photosynthetic rate(Pn), transpiration rate(Tr) and stomatal conductance(gs) occurred in D. glabrum var. trichocarpum and the lowest in S. microcarpa. On the contrary, D. glabrum var. trichocarpum had the lowest WUE, intrinsic water use efficiency(WUEi) and S. microcarpa had the highest. The results indicated that D. glabrum var. trichocarpum had higher photosynthetic capacity and poorer WUE, while S. microcarpa had lower photosynthetic capacity and greater WUE. Furthermore, the mean values of maximal fluorescence(Fm), potential efficiency of primary conversion of light energy of PS Ⅱ(Fv/Fm),ΦPSⅡ, actual efficiency of primary conversion of light energy of PSⅡ(F′v/F′m)and non-photochemical quenching coefficient(NPQ) were the highest in S. microcarpa, indicating that its PS Ⅱ had higher capacity of heat dissipation and could prevent photosynthetic apparatus from damage by excessive light energy. Correlation analysis showed that there were significant correlations among photosynthetic physiological parameters. However, the initial fluorescence(Fo) was not significantly correlated with any other parameters. This study also revealed the extremely significant positive correlations between Pn and Tr, gs, apparent quantum yield(AQY), between Tr and gs, between light saturation point(LSP) and AQY, between Fv/Fm and Fm, between ΦPSⅡ and photochemical quenching coefficient(qp), between Tr,gs and LSP, AQY. However, WUEiwas significantly negatively correlated with Tr,gs, Pn, LSP and AQY.