Adaptive Leaf Size

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

Key Concepts: o Convection: o The transfer of heat by the movement of a liquid or gas. (As opposed to radiation or conduction). LEAF LEAF A IR A IR

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

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

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

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

Warm Leaves o Wet Habitat: o water loss is not a problem o Maximizing photosynthesis is important o Sunny wet habitat: o Large leaf heats up past air temp (max photosynthesis) (max photosynthesis) o Shady wet habitat: o 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) (max temp and max photosynthesis)

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

Identification:

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