Adaptive Leaf SizeAdaptive Leaf Size

Purpose:Purpose:

oWhat determines the size of leaves?What determines the size of leaves?o Givnish and Vermeij (1976)Givnish and Vermeij (1976)

o suggested that leaf size is determined by suggested that leaf size is determined by the the heat budgetheat budget (the temp of the leaf) (the temp of the leaf)

oTest a model of optimal leaf size Test a model of optimal leaf size o Givnish and Vermeij (1976)Givnish and Vermeij (1976)

oTropical ForestsTropical Forests

Key Concepts:Key Concepts:

o Convection:Convection:

o The transfer of heat by the The transfer of heat by the movement of a liquid or gas. (As movement of a liquid or gas. (As opposed to radiation or opposed to radiation or conduction). conduction).

LEAF

A IR

Key Concepts: Key Concepts: contcont’’dd

o Boundary LayerBoundary Layero Layer of stagnant air Layer of stagnant air that naturally surrounds that naturally surrounds an objectan object

LEAF(profile view)

Air boundary layer

Key Concepts: Key Concepts: contcont’’dd

o Loss of heat to Leaf Convection depends on the Loss of heat to Leaf Convection depends on the boundary layerboundary layer

oBoundary layer thickness INCREASES with surface size.Boundary layer thickness INCREASES with surface size.

o Heat exchange DECREASES with boundary layer Heat exchange DECREASES with boundary layer thickness.thickness.

SMALL leaf(thin boundary layer)

LARGE leaf(thick boundary layer)

air

air

Key Concepts: Key Concepts: contcont’’dd

o EvapotranspirationEvapotranspiration

o Loss of water through stomata. Loss of water through stomata.

o All leaves lose heat through All leaves lose heat through evapotranspiration.evapotranspiration.

AssumptionsAssumptions::

o Temperature : Temperature : PhotosynthesisPhotosynthesiso Temperature : Temperature : Water lossWater loss

Warm LeavesWarm Leaveso Wet Habitat:Wet Habitat:

o water loss is not a problemwater loss is not a problemo Maximizing photosynthesis is importantMaximizing photosynthesis is important

o Sunny wet habitat:Sunny wet habitat:o Large leaf heats up past air temp Large leaf heats up past air temp

(max photosynthesis)(max photosynthesis)

o Shady wet habitat:Shady wet habitat:o Small leaf equilibrates with air. A large leaf would Small leaf equilibrates with air. A large leaf would become cool through evapotranspiration and retain become cool through evapotranspiration and retain that coolness because of its large boundary layer. that coolness because of its large boundary layer.

(max temp and max photosynthesis)(max temp and max photosynthesis)

Cool LeavesCool Leaveso Dry Habitat:Dry Habitat:

o Water loss = big problemWater loss = big problemo Water retention is importantWater retention is important

o Sunny dry habitat:Sunny dry habitat:o Small leaf equilibrates with airSmall leaf equilibrates with air (min temp and max water retention)(min temp and max water retention)

o Shady dry habitat:Shady dry habitat:o Large leaf remains cooler than air temp due to its Large leaf remains cooler than air temp due to its larger boundary layer. Becomes cooler due to larger boundary layer. Becomes cooler due to evapotranspiration. evapotranspiration. (max water retention)(max water retention)

Identification:Identification:

Methods:Methods:o Tuskegee Nat. Tuskegee Nat. ForestForesto Smilax glaucaSmilax glauca

o ““Greenbriar vineGreenbriar vine””

o 4 4 ““TreatmentsTreatments””::o Dry & SunnyDry & Sunnyo Dry & ShadyDry & Shadyo Wet & SunnyWet & Sunnyo Wet & ShadyWet & Shady

o Groups of 2Groups of 2o Measure (L & W)Measure (L & W)

o 30 leaves per 30 leaves per ““treatmenttreatment””o CentimetersCentimeterso Start with third leaf Start with third leaf backback

L

W