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Adaptive Leaf Size

Explore the relationship between leaf size and environmental factors in plant adaptation. Learn about the influence of heat budget and boundary layers on leaf size optimization for photosynthesis. Conduct experiments to understand the impact of temperature and water availability on leaf characteristics. Discover strategies for identifying ideal leaf sizes based on habitat conditions.

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Adaptive Leaf Size

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  1. Adaptive Leaf Size

  2. 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 • Givnish and Vermeij (1976) • Tropical Forests

  3. 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 A I R

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

  5. 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)

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

  7. Assumptions: •  Temperature :  Photosynthesis •  Temperature :  Water loss

  8. 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) Warm Leaves

  9. 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) Cool Leaves

  10. Identification:

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

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