While the majority of plants use the typical C3 carbon metabolic pathway, ~6% of angiosperms have adapted to carbon limitation as a result of water stress by employing a modified form of photosynthesis known as Crassulacean acid metabolism (CAM). CAM plants concentrate carbon in the cells by temporally separating atmospheric carbon acquisition from fixation into carbohydrates. CAM has been studied for decades, but the evolutionary progression from C3 to CAM remains obscure. In order to better understand the morphological and physiological characteristics associated with CAM photosynthesis, phenotypic variation was assessed in Yucca aloifolia, a CAM species, Yucca filamentosa, a C3 species, and Yucca gloriosa, a hybrid species derived from these two yuccas exhibiting intermediate C3–CAM characteristics. Gas exchange, titratable leaf acidity, and leaf anatomical traits of all three species were assayed in a common garden under well-watered and drought-stressed conditions. Yucca gloriosa showed intermediate phenotypes for nearly all traits measured, including the ability to acquire carbon at night. Using the variation found among individuals of all three species, correlations between traits were assessed to better understand how leaf anatomy and CAM physiology are related. Yucca gloriosa may be constrained by a number of traits which prevent it from using CAM to as high a degree as Y. aloifolia. The intermediate nature of Y. gloriosa makes it a promising system in which to study the evolution of CAM.

Leaf phenotype dataData from all genotypes from all three species including measures of leaf succulence, cross sectional data, and stomatal densities. See second tab for information on units.leaf_phenotype_data.xlsxRaw cross section dataData collected from cross section replicates from all three species and all genotypes.crosssections.xlsxLiCOR 6400XT dataGas exchange, etc data from all species for all days/timespoints and all experimental months (July and Oct 2014, Feb 2015). First five tabs are all data from a given day in an experiment, followed by tabs for species specific and genotype specific values.licor_data_alldays_allspecies.xlsxTitratable acidityTitratable acidity values (and raw pH values where measured) for all samples, all species.leaf_acidity.xlsx