Photosynthetic pathways in B romeliaceae: phylogenetic and ecological significance of CAM and C 3 based on carbon isotope ratios for 1893 species

A comprehensive analysis of photosynthetic pathways in relation to phylogeny and elevational distribution was conducted in B romeliaceae, an ecologically diverse Neotropical family containing large numbers of both terrestrial and epiphytic species. Tissue carbon isotope ratio ( δ 13 C ) was used to determine the occurrence of crassulacean acid metabolism ( CAM ) and C 3 photosynthesis in 1893 species, representing 57% of species and all 56 genera in the family. The frequency of δ 13 C 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 C 3 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 B romeliaceae, B rocchinioideae, L indmanioideae and N avioideae consisted entirely of C 3 species, with CAM species being restricted to H echtioideae (all species of H echtia tested), P itcairnioideae (all species belonging to a xeric clade comprising D euterocohnia , D yckia and E ncholirium ) and P uyoideae (21% of P uya spp.). Of the other two subfamilies, in the overwhelmingly epiphytic (plus lithophytic) Tillandsioideae, 28% of species possessed CAM photosynthesis, all restricted to the derived genus T illandsia and tending towards the more extreme epiphytic ‘atmospheric’ life‐form. In B romelioideae, with comparable numbers of terrestrial and epiphytic species, 90% of taxa showed CAM ; included in these are the first records of CAM photosynthesis in A ndrolepis , C anistropsis , D einacanthon , D isteganthus , E dmundoa , E duandrea , H ohenbergiopsis , L ymania , P seudananas , R onnbergia and U rsulaea . With respect to elevational gradients, the greatest number of C 3 bromeliad species were found at mid‐elevations between 500 and 1500 m, whereas the frequency of CAM species declined monotonically with increasing elevation. However, in P uya , at least ten CAM species have been recorded at elevations > 3000 m, showing that CAM photosynthesis is not necessarily incompatible with low temperatures. This survey identifies five major origins of CAM photosynthesis at a higher taxonomic level in B romeliaceae, but future phylogenetic work is likely to reveal a more fine‐scale pattern of gains and losses of this trait, especially in ecologically diverse and widely distributed genera such as Tillandsia and Puya . © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 178, 169–221.