PHYSIOLOGICAL ECOLOGY OF THE BROMELIACEAE

The physiological ecology of members of the Bromeliaceae is reviewed w ith an emphasis on photosynthesis and water relations. Terrestrial and epiphytic species are, for the most part, treated separately. Water r elations, photosynthetic pathways, and photosynthetic responses to lig ht, temperature, drought, atmospheric moisture, elemental nutrients, a nd pollutants are considered from an ecological perspective. In additi on, appendices provide values of numerous ecophysiological parameters for all species studied thus far. Results of this review include the f ollowing: (1) the ecophysiology of terrestrial and epiphytic species i s surprisingly similar; (2) approximately two-thirds of bromeliads are CAM plants and occupy arid sites or are epiphytic; (3) many species a re adapted to full or partial shade, yet can grow in full sunlight; (4 ) photosynthesis is optimal when day temperatures are warm and night t emperatures are cool; (5) species with heavy trichome indumenta on the ir leaf surfaces are capable of absorbing atmospheric water vapor, yet improvement of tissue water relations is unlikely; (6) heavy trichome covers also suppress CO2 exchange when leaf surfaces are wetted; (7) high levels of recycling of respiratory CO2) via CAM occur in many spe cies, especially under stress; and (8) tissue osmotic and water potent ials of nearly all bromeliads investigated are seldom more negative th an -1.0 MPa. A potential explanation of the mechanisms underlying main tenance of high tissue water potentials despite large water losses dur ing droughts is discussed. In summary, the diversity of physiological adaptations to the environment in the few bromeliads studied thus far is impressive, but likely will be surpassed with investigation of more species in the Bromeliaceae.