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