In the epiphytic tillandsioids, Guzmania monostachia, Werauhia sanguinolenta, and Guzmania lingulata (Bromeliaceae), juvenile plants exhibit an atmospheric habit, whereas in adult plants the leaf bases overlap and form water-holding tanks. CO2 gas-exchange measurements of the whole, intact plants and δ13C values of mature leaves demonstrated that C3 photosynthesis was the principal pathway of CO2 assimilation in juveniles and adults of all three species. Nonetheless, irrespective of plant size, all three species were able to display features of facultative CAM when exposed to drought stress. The capacity for CAM was the greatest in G. monostachia, allowing drought-stressed juvenile and adult plants to exhibit net CO2 uptake at night. CAM expression was markedly lower in W. sanguinolenta, and minimal in G. lingulata. In both species, low-level CAM merely sufficed to reduce nocturnal respiratory net loss of CO2. δ13C values were generally less negative in juveniles than in adult plants, probably indicating increased diffusional limitation of CO2 uptake in juveniles., J. D. Beltrán ... [et al. ]., and Obsahuje bibliografii
Clusia is a widely distributed neotropical genus with 321 currently described species. This remarkable genus is the only one known to contain trees sensu stricto with CAM photosynthesis. To survey the occurrence of CAM in Clusia species from Colombia, we determined the leaf stable carbon isotope composition (δ13C) of 568 specimens from 114 species deposited in 12 Colombian herbaria. In the vast majority of specimens, δ13C values indicated that C3 photosynthesis was the principal contributor to carbon gain. δ13C values typical of strong CAM (less negative than -20‰) were observed in only five species, in four of them for the first time. All samples with CAM-type isotopic signatures were collected below 1,000 m a.s.l., whereas species with predominantly C3 occurred from sea level to 3,500 m a.s.l. Together with information already available in the literature, we conclude that CAM is present in 22% (35/156) of the species of Clusia investigated thus far.