Crassulacean acid metabolism in the epiphytic fern Platycerium bifurcatum

The epiphytic fern Platycerium bifurcatum grows in different habitats characterized by drought and high irradiance stress. The plant shows diurnal malate oscillations, indicative for CAM expression only in cover leaves, but not in sporotrophophyll. In P. bifurcatum cover leaves exposed to high irradiance and desiccation, the decrease in both CO(2) assimilation (P(N)) and stomatal conductance (g(s)) was accompanied with occurrence of diurnal malate oscillations. Exogenously applied abscisic acid (ABA) induced the decrease in P(N) and g(s), but no clear change in malate oscillations. The measurements of the maximum quantum efficiency of photosystem 2 (F(v)/F(m)) under high irradiance showed distinct photoinhibition, but no clear changes in F(v)/F(m) due to desiccation and ABA-treatment were found.