? 13C values and crassulacean acid metabolism in Clusia species from Panama

Abstract

The genus Clusia is notable in that it contains arborescent crassulacean acid metabolism (CAM) plants. As part of a study of CAM in Clusia, titratable acidities were measured in 25 species and δ 13C values were measured for 38 species from Panama, including seven undescribed species, and 11 species from Colombia, Costa Rica and Honduras. CAM was detected in 12 species. Clusia flava, C. rosea and C. uvitana exhibited δ 13C values or diurnal fluctuations in acidity indicative of strong CAM. In C. croatii, C. cylindrica, C. fructiangusta, C. lineata, C. odorata, C. pratensis, C. quadrangula, C. valerioi and C. sp. D diurnal fluctuations in acidity were consistent with weak CAM but the δ 13C values were C3-like. All of the species that exhibited strong or weak CAM were in the C. flava or C. minor species groups. CAM was not detected in any member of the C. multiflora species group. Strong CAM species were not collected at altitudes above 680 m a.s.l. On the basis of δ 13C values, the expression of CAM was similar in terrestrial, hemi-epiphytic and epiphytic species and did not differ between individuals of the same species that exhibited different life-forms. This study indicates that phylogenetic affiliation may be a predictor of an ability to exhibit CAM in Clusia species from the Panamanian region, and that weak CAM is probably a common photosynthetic option in many Clusia species. δ 13C value is not a particularly good indicator of a potential of Clusia species growing in the field to exhibit CAM because it appears that the contribution in most species of CAM to carbon gain is generally rather small when integrated over the life-time of leaves.