The occurrence of crassulacean acid metabolism in Cymbidium (Orchidaceae) and its ecological and evolutionary implications

Abstract

Crassulacean acid metabolism (CAM) is one of the photosynthetic pathways regarded as adaptations to water stress in land plants. Little is known about correlations among the level of CAM activity, environment of habitat, life form, and phylogenetic relationship of a plant group from an evolutionary perspective. We examined these relationships in 18 species of Cymbidium (Orchidaceae) because the genus shows distinctive diversification of habitats and life forms. The photosynthetic type was classed into three categories, strong CAM, weak CAM, and C(3) on the basis of CAM activity. CAM expression in Cymbidium was confined to the epiphytic and lithophytic species. Especially, all of these species from tropical to subtropical rainforest exhibited CAM activity. On the other hand, the terrestrial species always exhibited C(3) metabolism irrespective of their varied habitats. Regarding the evolution of photosynthetic characters, weak CAM was the ancestral state in Cymbidium and strong CAM and C(3) metabolism occurred subsequently. The evolution of strong CAM likely enabled Cymbidium to extend to exposed sites in tropical lowland where marked water stress exists. Further, different levels of CAM activity characterized each species and such potential plasticity of CAM may realize the radiation of Cymbidium into sites with different environmental conditions.

Crassulacean Acid Metabolism and Epiphytism Linked to Adaptive Radiations in the Orchidaceae

“…C bimodal distribution found in this study is consistent with other studies (Griffiths and Smith, 1983;Pierce et al, 2002;Holtum et al, 2004;Silvera et al, 2005;Motomura et al, 2008) showing disruptive selection on C 3 photosynthesis and strong CAM d…”

“…Whitten, N.H. Williams, K. Winter, and J.C. Cushman, unpublished data). A recent study using the genus Cymbidium concluded that weak CAM was the ancestral state and that C 3 and strong CAM were derived (Motomura et al, 2008). However, the results were restricted to species within one genus and limit the conclusions that can be applied at the family level.…”

Evolution along the crassulacean acid metabolism continuum

“…Studies with limited taxon sampling by d 13 C analysis have been reported for the Crassulaceae (Kalanchoë) (Kluge et al 1991), Sedum and Aeonium (PilonSmits et al 1996), Clusiaceae (Gehrig et al 2003;Gustafson et al 2007), and Orchidaceae (Cymbidium) (Motomura et al 2008). More extensive combined taxon and isotopic sampling has been completed within the Bromeliaceae (Crayn et al 2004) and the Orchidaceae (Silvera et al 2009(Silvera et al , 2010.…”

Crassulacean Acid Metabolism in Epiphytic Orchids: Current Knowledge, Future Perspectives

“…During daytime, de-acidification occurs and stomata are closed (Goh et al, 1977). In a study of eighteen Cymbidium species, Motomura et al (2008b) verified that there are different CAM intensities, ranging from weak to strong. They found that three strong CAM Cymbidium species have thicker leaves than other species: >1.0 mm and <0.7 mm, respectively.…”

“…The typical range of δ 13 C‰ for C 3 plants is between -33‰ to -22.1‰, while for strong CAM plants it ranges from -22‰ to -12‰ (Elheringer & Osmond, 1989). Several studies done in different taxa have shown a bimodal pattern of the frequency distribution of δ 13 C‰ values among orchid species, following their photosynthetic pathway (Holtum et al, 2005;Motomura et al, 2008b;Pierce et al, 2002;Silvera et al, 2005Silvera et al, , 2009Silvera et al, , 2010aSilvera et al, , 2010b; this behavior is characterized by a cluster formed by a high number of C 3 species (indicated by values near -28‰) and a smaller cluster formed by CAM species (with values near -16‰); between the clusters are intermediate values that could represent weak CAM or facultative CAM species (usually in response to a stress, such as drought) (Silvera et al, 2009). In fact, it was found that although some orchid species presented δ 13 C‰ values typical of a C 3 plant, they were capable of nighttime carbon fixation, reflected by an increase in tissue titratable acidity (Silvera et al, 2005).…”