Smith 2015 (Conference Paper) Bromeliaceae, cam

CAM photosynthesis as an adaptive feature in the ecophysiology and evolution of Bromeliaceae

Author(s):—Andrew Smith in Benko-Iseppon, A.M.; Alves, M. & Louzada, R. (2015) An overview and abstracts of the First World Congress on Bromeliaceae Evolution. Rodriguésia 66(2): A1-A66.

Publication:— (2015).

Abstract:—The Bromeliaceae represent an exceptionally diverse family of vascular plants in their range of life-forms and ecology. Nowhere is this more striking than in the variation in water availability that characterizes the habitatsof different bromeliads, extending from the high-precipitation environments of true tropical rain forests to the hyperarid deserts of Chile and Peru. Associated with these habitats, bromeliads are confronted with a correspondingly wide range of temperature regimes (from lowland equatorial sites to high-elevation niches in the Andes) and light intensities (from fully exposed terrestrial sites and the tops of forest canopies to the shaded understory of lowland forests). As part of their adaptation to the more stressful habitats, especially with respect to limited availability of water, nearly half of all species of bromeliads have adopted the mode of photosynthesis known as crassulacean acid metabolism (CAM). This biochemical pathway allows plants totake up most or all of their CO2 from the atmosphere at night, and then to process the CO2 photosyntheticallyduring the following daytime behind closed stomata, resulting in much reduced loss of water in transpiration compared with C3 photosynthesis. Detailed taxonomic surveys of stable-carbon-isotope discrimination within Bromeliaceae have shown that nearly half of all species possess the CAM pathway, exhibiting a strong correlation with leaf morphology (succulence) and habitat aridity. When mapped onto a well-resolved phylogeny of genera within the family, it can be inferred that CAM photosynthesis has arisen a minimum of five times within Bromeliaceae, four of which represent clades of terrestrial xeromorphic succulents and the fifth the more extreme epiphytic members of Tillandsia. Rate calibration of the bromeliad phylogeny indicates that the diversification of these CAM lineages took place in the late Miocene and Pliocene, coincident in part with the emergence of specific semi-arid biomes and the creation of hyperdiverse montane habitats during the final uplift of the northern Andes. More detailed work is now underway using species distribution modelling to characterize the ecological niche of the CAM bromeliads with respect to various environmental axes and to explore possible reasons for the apparent paucity of C3?CAM intermediates. The results suggest that photosynthetic pathway distribution in the family is dominated by a pattern of phylogenetic niche conservatism superimposed on a limited number of intermediate or plastic phenotypes that tend to be restricted to ecologically marginal habitats.

Keywords:—Photosynthesis; Water Relations; Ecophysiology.