Abstract
The relationship between leaf anatomy, specifically the percent of leaf volume occupied by waterstorage parenchyma (hydrenchyma), and the contribution of respiratory CO<sub>2</sub> during Crassulacean acid metabolism (CAM) was investigated in 12 epiphytic species of Tillandsia. It has been postulated that the hydrenchyma, which contributes to CO<sub>2</sub> exchange through respiration only, may be causally related to the recently observed phenomenon of CO<sub>2</sub> recycling during CAM. Among the 12 species of Tillandsia, leaves of T. usneoides and T. bergeri exhibited 0% hydrenchyma, while the hydrenchyma in the other species ranged from 2.9% to 53% of leaf cross-sectional area. Diurnal malate fluctuation and nighttime atmospheric CO<sub>2</sub> uptake were measured in at least four individuals of each species. A significant excess of diurnal malate fluctuation as compared with atmospheric CO<sub>2</sub> absorbed overnight was observed only in T. schiedeana. This species had an intermediate proportion (30%) of hydrenchyma in its leaves. Results of this study do not support the hypothesis that CO<sub>2</sub> recycling during CAM may reflect respiratory contributions of CO<sub>2</sub> from the tissue hydrenchyma.
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