XVI International Botanical Congess

Dendrobium crumenatum and Epidendrum Pretty Lady" are CAM (crassulacean acid metabolism) orchids. In the presence of increasing photosynthetic photon flux density in the day, internal CO2 increased through increasing malate decarboxylation in the leaf cells. The proportion of thermal dissipation (NPQ) and the reduction state of PSII (1-qP) decreased, while the proportation of open PSII centres (qP) remained unchanged at midday. Upon exposure of the leaves to CO2-free air, titratable acidity decreased. The thermal heat dissipation in these leaves at mid-day increased sharply, while the quantum efficiency of PSII (Fv/Fm) and qP decreased. Thus, CAM activity seemed to be able to protect the orchids from photodamage.