Leaf water repellency as an adaptation to tropical montane cloud forest environments

Adaptations that reduce water retention on leaf surfaces may increase photosynthetic capacity of cloud forests because carbon dioxide diffuses slower in water than air. Leaf water repellency was examined in three distinct ecosystems to test the hypothesis that tropical montane cloud forest species have a higher degree of leaf water repellency than species from tropical dry forests and species from temperate foothills-grassland vegetation. Leaf water repellency was measured by calculating the contact angle of the leaf surface and the line tangent to a water droplet through the point of contact on the adaxial and the abaxial surface. Leaf water repellency was significantly different between the three study areas. The hypothesis that leaf water repellency is higher in cloud forest species than tropical dry forests and temperate foothills-grassland vegetation was not confirmed in this study. Leaf water repellency was lower for cloud forest species (adaxial surface = 50.8 degrees; abaxial surface = 82.9 degrees) than tropical dry forest species (adaxial surface = 74.5 degrees; abaxial surface = 87.3 degrees) and temperate foothills-grassland species (adaxial surface = 77.6 degrees; abaxial surface = 95.8 degrees). The low values of leaf water repellency in cloud forest species may be influenced by presence of epiphylls and loss of epicuticular wax on the leaf surfaces.