Comparative ecophysiology of CAM and C3 bromeliads. I. The ecology of the Bromeliaceae in Trinidad
SMITH JAC., GRIFFITHS H., LÜTTGE U.
Abstract This article deals with the physiological ecology of the Bromeliaceae, a large neotropical family containing both terrestrial and epiphytic forms, as well as many species with crassulacean acid metabolism (CAM). The article is in two parts. In the first, we review what is known of the occurrence of CAM and C3 species in the Bromeliaceae. The photosynthetic pathways are discussed in the context of the major taxonomic divisions within the family and the great diversity of bromeliad life‐forms. Of the three subfamilies, the Pitcairnioideae contain both C3 and CAM species and are essentially all terrestrial. In contrast, the Tillandsioideae are entirely epiphytic or saxicolous, with CAM species being restricted to the genus Tillandsia, And in the Bromelioideae all species show CAM, but terrestrial and epiphytic forms are found in about equal numbers. The evidence suggests that both CAM and the epiphytic habit arose more than once in the family's evolutionary history. In the second part we consider the photosynthetic ecology of the various bromeliad life‐forms in more detail using the specific example of Trinidad (West Indies). CAM bromeliads tend to be centred on the drier regions of the island and C3 forms on the wetter areas. However, at any one site there is a marked vertical stratification of species within the forest profile. Based on the known habitat preferences of the bromeliads, six contrasting sites were selected for field studies in Trinidad. These ranged from arid coastal scrub to montane rain forest, the vegetational and climatic characteristics of which are described here. The constancy of δ13C values (carbon‐isotope ratios) for individual CAM species in these markedly different habitats emphasized the need for ecophysiological studies to characterize environmental effects on CO2 assimilation and transpiration. The following papers in this series present the results of a comparative investigation of gas exchange and leaf water relations of CAM and C3 bromeliads in situ at the various sites. Copyright © 1986, Wiley Blackwell. All rights reserved