Leaf water repellency of species in Guatemala and Colorado (USA) and its significance to forest hydrology studies

Abstract

Fog persistency and high precipitation totals contribute to the unique ecohydrology of tropical montane cloud forests. The persistence of water droplets on leaf surfaces in cloud forests inhibits photosynthetic carbon exchange because carbon dioxide diffuses slower in water than air. Adaptations that reduce water retention on leaf surfaces may increase photosynthetic capacity of cloud forests. The objective of the present study was to determine if 12 cloud forest species from the Sierra de las Minas, Guatemala have a higher degree of leaf water repellency than 12 species from tropical dry forests in Chiquimula, Guatemala and 12 species from foothills–grassland vegetation in Colorado (USA). Leaf water repellency was measured as the contact angle between the leaf surface and the line tangent to the water droplet passing through the point of contact between the droplet and the leaf surface. Analysis of variance indicated that leaf water repellency was significantly different between the three study areas; however, the leaf water repellency of 12 species in the Sierra de las Minas was lower than 12 species in Chiquimula and lower than the leaf water repellency of 12 species in Colorado. Leaf water repellency of abaxial surfaces of all species in the cloud forest (Sierra de las Minas) was greater leaf water repellency of adaxial surfaces. The low values of leaf water repellency in cloud forest species may be influenced by presence of epiphylls or the loss of epicuticular wax on the leaf surfaces because of high precipitation totals and longer leaf life-span. High leaf water repellency in dry climates may be an adaptation to increase hydrological inputs underneath the canopy.