Photosynthetic pathways in Bromeliaceae: phylogenetic and ecological significance of CAM and C3 based on carbon isotope ratios for 1893 species

A comprehensive analysis of photosynthetic pathways in relation to phylogeny and elevational distribution was conducted in Bromeliaceae, an ecologically diverse Neotropical family containing large numbers of both terrestrial and epiphytic species. Tissue carbon isotope ratio (δ13C) was used to determine the occurrence of crassulacean acid metabolism (CAM) and C3 photosynthesis in 1893 species, representing 57% of species and all 56 genera in the family. The frequency of δ13C values showed a strongly bimodal distribution: 1074 species (57%) had values more negative than −20‰ (mode = −26.7‰), typical of predominantly daytime carbon fixation via the C3 pathway, whereas 819 species (43%) possessed values less negative than −20‰ (mode = −13.3‰), indicative of predominantly nocturnal fixation of carbon via the CAM pathway. Amongst the six almost exclusively terrestrial subfamilies in Bromeliaceae, Brocchinioideae, Lindmanioideae and Navioideae consisted entirely of C3 species, with CAM specie...