刺栲（Castanopsis hystrix）的气体交换和叶绿素a荧光特征

Characteristics of Gas Exchange and Chlorophyll a Fluorescence in Leaves of Castanopsis hystrix

摘要:

用LI-6400便携式光合测定系统和PAM-2100便携式植物荧光分析仪分别在初夏和秋季测定了广州龙眼洞林场刺栲（Castanopsis hystrix）幼树叶片的气体交换和叶绿素a荧光参数.结果表明：1）刺栲冠层阳生叶的光饱和点为400 μ mol photons m^-2s^-1,最大光合速率在4-6 μ mol m^-2s^-1之间,说明刺栲幼树保持阳生植物的特征.阴生叶与阳生叶的叶绿素a/b值相似,均约为2.4,而阴生叶叶绿素b含量高于阳生叶,表明阴生叶具有潜在利用弱光的能力；2）刺栲幼树冠层叶片的PSⅡ的最大光化学效率Fv/Fm和光化学量子产额（Yield）的日动态变化在中午略有下降,说明其在强光下能发生可逆性的光抑制.刺栲冠层阳生叶的最大光合能力比较低,整个冠层叶能高效而稳定地利用散射和透射光,这些特征使得常绿的刺栲幼树能在林边或林下良好生长,较好地适应不同的光环境并成功渡过幼苗期,最终成为群落中的上层优势种.

Abstract:

Photosynthetic characteristics in leaves of Castanopsis hystrix saplings in Longyandong Forestry, Guangzhou, were studied during early summer and autumn under natural conditions by leaf gas exchange and chlorophyll fluorescence techniques. The light saturation point （LSP） of sun leaves in canopy was 400 μ mol photons m^-2s^-1, and the maximum net photosynthetic rate was 4-6 μ mol m^-2s^-1. These data showed that C. hystrix saplings are sun plants. The values of chlorophyll a/b in sun leaves and shade leaves were both upto 2.4, and the content of chlorophyll b in shade leaves was higher than that in sun leaves, indicating that shade leaves in canopy had the potential ability to utilize low light intensity. The daily changes in chlorophyll fluorescence parameters recorded that maximum photochemical efficiency of PSⅡ(Fv/Fm) and photochemical quantum yield of PS Ⅱ (Yield) in sun leaves of C. hystrix canopy declined slightly at the midday, suggesting the occurrence of reversible photoinhibition. Owing to the lower maximum net photosynthetic rate in sun leaves and the ability to effectively and consistently utilize the scattered light and/or transmitted light, C. hystrix saplings could survive low light intensity, grow well at the edge of the forest and in the understorey, and eventually become one of the dominant species in upper layer of the community.