全光和遮阴下两种亚热带木本植物的光合作用对光的响应

PHOTOSYNTHETIC RESPONSES OF TWO SUBTROPICAL WOODY PLANTS GROWING UNDER SUN AND SHADE ENVI RONMENTS

摘要:

以气体交换和调制叶绿素荧光测定技术测定了2年生亚热带乔木黧蒴、林下灌木九节在全自然光和17%自然光下叶片同部位的光合作用和与之相关的荧光参数的日变化。和全光照比较,遮阴下植物叶片净光合速率Pn、气孔导度g_s、胞间CO₂浓度与大气CO₂浓度之比Ci/Ca,类胡萝卜素与叶绿素含量之比Car/Chl、光系统II原初光化学效率Fv/Fm的变化幅度相对较小,种间差异较不明显。全光照黧蒴和九节Pn的日变化图式与gS、Ci/Ca类似,与ФPSII、q_P的下降吻合。全光下黧蒴叶片q_N和Car/Chl的日进程表现为增加,九节则下降,低的Car/Chl可能是导致强光下九节未能提高其qN的原因。正午前后,黧蒴q_N和Car/Chl增大,而q_P和Ф_PSII降低,Fv/Fm则保持相对稳定,反映其开放的PSII反应中心数目在此期间虽有所减少,但仍然维持了较高的光化学效率,提高的Car/Chl和qN则说明其具有较强的对过剩激发能的耗散能力。此条件下九节的g_s、Fv/Fm和q_N下降且明显低于黧蒴,Ф_PSII和q_P保持相对稳定但高于黧蒴的水平,表明九节的PSII反应中心活性较稳定,但强光下气孔部分关闭、较低的Fv/Fm和q_N限制了CO₂供应和对光能的有效利用，且未能诱导热能耗散机制的积极运行及对光合器起到保护作用。总体上说，九节对高光强反应比黧蒴敏感。

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 (g_s) 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，g_s and Ci/Ca for the two species generally declined with time, consistently with the decrease of the q_P and Ф_PSII．q_N and Car/Chl for Castanopsis fissa increased with time， but decreased for Psychotria rubra． The decrease of q_P and Ф_PSII 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 q_N suggested that the excessive activated energy could be safely dissipated．While for Psychotria rubra, the g_s q_N and Fv/Fm decreased and were significantly lower, but Ф_PSII and q_P 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.