LEAF ANATOMY AND CO-2 RECYCLING DURING CRASSULACEAN ACID METABOLISM IN 12 EPIPHYTIC SPECIES OF TILLANDSIA (BROMELIACEAE)

The relationship between leaf anatomy, specifically the percent of leaf volume occupied by water-storage parenchyma (hydrenchyma), and the contribution of respiratory CO2 during Crassulacean acid metabolism (CAM) was investigated in 12 epiphytic species of Tillandsia. It has been postulated that the hydrenchyma, which contributes to CO2 exchange through respiration only, may be causally related to the recently observed phenomenon of CO2 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 CO2 uptake were measured in at least four individuals of each species. A significant excess of diurnal malate fluctuation as compared with atmospheric CO2 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 CO2 recycling during CAM may reflect respiratory contributions of CO2 from the tissue hydrenchyma.