Abstract:Photosynthesis and fluorescence parameters involving photosynthetic process in the leaves of 2-year-old subtropical tree species Castanopsis fissa and understory shrub Psychotria rubra were determined by using gas exchange and fluorescence techniques，which were transplanted in 25 plots for 6 months under flIl sunlight and shade (17％ of full sunlight)for each treatment The daily course variation of net photosynthesis rate (Pn)，stomatal conductance (gs) ratio of intercellular to ambient CO2 concentration (Ci/Ca)，ratio of carotenoid to chlorophyll content (Car/Chl)，and the efficiency of photochemical reaction (Fv/Fm) for both plants under shade were relatively stable and less difference between species．However，in full sunlight，the Pn，gs and Ci/Ca for the two species generally declined with time, consistently with the decrease of the qP and ФPSII．qN and Car/Chl for Castanopsis fissa increased with time， but decreased for Psychotria rubra． The decrease of qP and ФPSII in leaves of Castanopsis fissa under full sunlight around the noon time indicated that the numbers of tlle open PSII reaction center were possibly reduced，but its photochem ical efficiency still maintained at a relativdly stable level indicated by Fv/Fm．Meanwhile，the increase in Car/Chl and qN suggested that the excessive activated energy could be safely dissipated．While for Psychotria rubra, the gs qN and Fv/Fm decreased and were significantly lower, but ФPSII and qP maintained relatively stable and were higher as compared to Castanopsis fissa, implying that its PSII reaction center may change a little， but CO2 exchange， photochemical efficiency, and heat dissipation capacny had been weakened to acertain degree．In general，Psychotria rubra showed more sensitivi to strong light intensity than Castanopsis fissa.