From epiphyte to tree: differences in leaf structure and leaf water relations associated with the transition in growth form in eight species of hemiepiphytes


N. Michele Holbrook, Biological Laboratories, 16 Divinity Ave., Harvard University, Cambridge, MA 02138, USA


Stranglers must undergo a transformation in growth form from epiphyte to tree to become reproductive mature and thus require developmental and/or physiological plasticity to cope with radical changes in their rooting environment. Differences in leaf structure and water relations between epiphytic-phase and free-standing individuals were marked in the five Ficus species examined. Epiphytic Ficus had several-fold higher specific leaf area (cm2 g−1) and 2- to 4-fold lower stomatal densities than conspecific trees. Osmotic potentials at full saturation were, on average, 0-6 MPa higher (less negative) and the bulk modulus of elasticity approximately 50% lower in epiphytic plants than in conspecific trees. This resulted in leaves of epiphytic and tree individuals losing turgor at approximately the same relative water content, hut at a substantially higher leaf water potential in the epiphytic plants. In contrast, differences in leaf structure and water relations between epiphytes and trees of Clusia minor and Coussapoa villosa were small. In greenhouse experiments, alteration of the water and nutrient supply to epiphytic F. tuerckheimmii plants did not lead to significant changes in leaf structure.