Abstract: Two Cypripedium species ( C. flavum , C. tibeticum) were selected to investigate the effects of flowering on photosynthesis and allocation of assimilation product by measuring leaf gas exchange, actual quantum efficiency of photosystem
Ⅱ photochemistry (ΦPSⅡ ) and allocation of 14 C. Both ΦPSⅡ and light-saturated rate of electron transport ( Jmax ) were significantly higher in flowering plants than those in nonflowering plants , suggesting that higher photosynthetic rate in flowering plants resulted from the increasing rate of electron transport . Respiratory rate of C. tibeticum was 112% higher in
flowering plants than in nonflowering plants, however , the flowering plants of C. flavum only showed an increase of respiratory rate by 22% . This result indicated that flowering of C. tibeticum was expending more energy than that of C. flavum, so there was no significant increase of maximal net photosynthetic rate (Amax ) in flowering C. tibeticum . 14 C allocation showed that the flower and the belowground parts including rhizomes and buds competed each other for assimilation product. Therefore the proportion of assimilation product transferred to the underground parts was reduced by flowering .

Key words: Flowering

摘要： 对同一生境下黄花杓兰( Cypripedium flavum) 和西藏杓兰( Cypripedium tibeticum) 开花株与非开花株的气体交换、光系统Ⅱ实际光化学效率(ΦPSⅡ ) 和14 C 分配进行了测定, 目的在于了解开花对杓兰光合作用以及同化产物分配的影响。结果表明这两种杓兰开花均能通过提高电子传递速率来提升植株的光合作用。相对于黄花杓兰, 西藏杓兰开花显著提高植株的呼吸速率, 以致其最大净光合速率(Amax ) 的提升不显著。两种杓兰的花和地下部分(包括根状茎和芽) 在同化产物分配上存在竞争关系, 因而开花减少了同化产物向植株地下部分的分配。

关键词: 开花, 光合作用, 电子传递速率, 同化产物分配FONT