Photosynthesis in relation to reproductive success of Cypripedium flavum

Cypripedium flavum is a rare, endemic alpine slipper orchid of China, which is under threat from excessive collection and habitat changes. Conservation and re-introduction of C. flavum is restricted by lack of knowledge of the plant's photosynthesis and how that affects reproductive success. The hypothesis is tested that reproductive success is determined by photosynthetic production. *

To understand the photosynthetic characteristics and adaptation of C. flavum to alpine environments, and the relation to reproductive success, measurements were made at four field sites with varying degrees of forest cover in the Hengduan Mountains, south-west China. *

Both photosynthetic capacity and reproductive traits of C. flavum are affected by light availability. Photosynthetic rate (A) is greatest around noon, following the pattern of photosynthetically active radiation (PAR) at all sites. Cypripedium flavum has highest daily mean photosynthetic rate (A(daily)) and light-saturated photosynthetic rate (A(max)) under a half to a third of full sunlight. High radiation decreased A. However, the optimum temperature for photosynthesis was similar (18-20 degrees C) at all sites. *

The quotient of daily mean photosynthetic rate to light saturated photosynthesis (A(daily)/A(max)) is positively correlated with the ramet number m(-2) and percentage of fruiting of C. flavum. The A(daily)/A(max) ratio is a useful proxy for evaluating reproductive success of C. flavum.