Physiological consequences of changes in life form of the Mexican epiphyte Tillandsia deppeana (Bromeliaceae).

The heterophyllous epiphyte Tillandsia deppeana exhibits an atmospheric habit as a juvenile and a tank form as an adult. Both juveniles and adults utilize C photosynthesis. This is the first report of an atmospheric form of Tillandsia which does not exhibit CAM. Photosynthetic saturation occurred at approximately 10% of full sunlight in both forms, but the adults exhibited greater rates of photosynthesis at all levels of irradiance. The adults also had a higher and broader photosynthetic temperature optimum than did the juveniles. The adults transpired at greater rates than the juveniles; however, the water use efficiencies of both forms were similar and were high for C plants. In both forms the photosynthetic rate decreased in response to a decrease in humidity. After 8 days without water the juveniles were able to fix CO throughout the day. The adults, however, exhibited a net loss of CO on the second day without water and thereafter. These results indicate that the water-conservative atmospheric juvenile of T. deppeana is well adapted to establishment in the epiphytic habitat.