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Juvenile tank-bromeliads lacking tanks: do they engage in CAM photosynthesis?

Beltrán, J. D., Lasso, E., Madriñán, S., Virgo, A., Winter, K.
Photosynthetica 2013 v.51 no.1 pp. 55-62
C3 photosynthesis, Crassulacean acid metabolism, Guzmania, adults, carbon dioxide, juveniles, leaves, mature plants, tanks, water stress
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.