PHYSIOLOGICAL ECOLOGY OF THE BROMELIACEAE

The physiological ecology of members of the Bromeliaceae is reviewed with an emphasis on photosynthesis and water relations. Terrestrial and epiphytic species are, for the most part, treated separately. Water relations, photosynthetic pathways, and photosynthetic responses to light, temperature, drought, atmospheric moisture, elemental nutrients, and pollutants are considered from an ecological perspective. In addition, appendices provide values of numerous ecophysiological parameters for all species studied thus far. Results of this review include the following: (1) the ecophysiology of terrestrial and epiphytic species is surprisingly similar; (2) approximately two-thirds of bromeliads are CAM plants and occupy arid sites or are epiphytic; (3) many species are adapted to full or partial shade, yet can grow in full sunlight; (4) photosynthesis is optimal when day temperatures are warm and night temperatures are cool; (5) species with heavy trichome indumenta on their 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 species, especially under stress; and (8) tissue osmotic and water potentials of nearly all bromeliads investigated are seldom more negative than -1.0 MPa. A potential explanation of the mechanisms underlying maintenance of high tissue water potentials despite large water losses during 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.