Adaptive Leaf Size 1

Purpose: What determines the size of leaves? Givnish and Vermeij (1976) suggested that leaf size is determined by the heat budget (the temp of the leaf) Test a model of optimal leaf size Tropical Forests

Key Concepts: Convection: The transfer of heat by the movement of a liquid or gas. (As opposed to radiation or conduction). L E A F I R

Key Concepts: cont’d Boundary Layer Layer of stagnant air that naturally surrounds an object LEAF (profile view) Air boundary layer

(thick boundary layer) Key Concepts: cont’d Loss of heat to Leaf Convection depends on the boundary layer Boundary layer thickness INCREASES with surface size. Heat exchange DECREASES with boundary layer thickness. air air SMALL leaf (thin boundary layer) LARGE leaf (thick boundary layer)

Key Concepts: cont’d Evapotranspiration Loss of water through stomata. All leaves lose heat through evapotranspiration. 6

Assumptions:  Temperature :  Photosynthesis  Temperature :  Water loss

Warm Leaves Wet Habitat: water loss is not a problem Maximizing photosynthesis is important Sunny wet habitat: Large leaf heats up past air temp (max photosynthesis) Shady wet habitat: Small leaf equilibrates with air. A large leaf would become cool through evapotranspiration and retain that coolness because of its large boundary layer. (max temp and max photosynthesis)

Cool Leaves Dry Habitat: Water loss = big problem Water retention is important Sunny dry habitat: Small leaf equilibrates with air (min temp and max water retention) Shady dry habitat: Large leaf remains cooler than air temp due to its larger boundary layer. Becomes cooler due to evapotranspiration. (max water retention)

Identification: 10

Methods: Groups of 2 Tuskegee Nat. Forest Measure (L & W) Smilax glauca “Greenbriar vine” 4 “Treatments”: Dry & Sunny Dry & Shady Wet & Sunny Wet & Shady Groups of 2 Measure (L & W) 30 leaves per “treatment” Centimeters Start with third leaf back L W 11