Morphological variation of th leaves of Aechmea distichantha Lem. plants from contrasting habitats of a Chaco forest: a trade-off between leaf area and mechanical support

摘要

Sveral authors have reported phenotypic plasticity for bromeliad plants growing in contrasting habitats. Morphological and physiological differences of leaves seem to be an adaptation to water and light use, but there is also a compromise between carbon gain and the costs of sustaining static and dynamic loads. We hypothesized that plastic responses to habitat at the leaf level represent a trade-off between the photosynthetic area for capturing light and mechanical support. In this study, we measured morphological and architectural variables of central and basal leaves of Aechmea distichantha plants from the understory and forest edge, as well as anatomical variables of plants from each habitat. Understory plants had longer leaves, larger blade areas and greater length/width ratios than forest-edge plants. Blades of understory plants were less erect, less succulent, had thicker fiber tissue surrounding the vascular bundles and a higher curvature index than blades of forest-edge plants. Thus, understory plants increased their flexural stiffness by modifying their tissue structure as well as the shape of their leaves. On the other hand, blades of forest-edge plants had higher stomatal density and higher trichome density on their adaxial sides than understory plants. These patterns could be adaptations for higher gas exchange and to reduce vulnerability to photoinhibition in sun plants when compared to shade plants. Finally, most of the morphological and architectural variables were significantly different between positions. These results support our view that there is a trade-off at the leaf level between photosynthetic leaf area (for light capture and water use) and mechanical support.