Plant Ecology 5460 Energy Balance

We covered a small portion of this during lecture and discussed it when doing the E. californica vs E. farinosa research paper questions in groups.

What leaf traits influence leaf temperature?

1) Leaf orientation: perpendicular vs angled vs rolled

2) Leaf size

3) Pubescence)

4) Stomata conductance and transpiration

What is a boundary layer and what does it do?

The boundary layer is a thin zone of unmoving air against the surface of the leaf.

It acts as a buffer reducing transpiration and convective heat transfer.

A thick boundary layer traps humidity and heat, a thin boundary layer increases transfer with the environment.

A breeze can thin the boundary layer, increasing cooling and water loss.

Larger leaves have thicker boundary layers.

Pubescence thickens the boundary layer, trapping local air and conserving moisture.

Describe conduction and convection in terms of leaf temperature transfer.

Conduction: slow diffusion of heat in the boundary layer of stagnant air.

Convection: larger transfer of heat from free moving air currents, dependent on wind.

Describe how transpiration works to reduce leaf temperature.

During transpiration, liquid water comes to the surface of the leaf and it absorbs heat from the leaf as it becomes a gas but without changing temperature- called latent heat of vaporization.

Describe how pubescence helps reduce leaf temperature?

Pubescence increases the albedo of the leaves, reflecting more solar radiation and reducing leaf temperature.

For Encelia Californica (no pubescence, lives in a mild stable climate) were there differences in maximum photosynthetic rate and quantum yield between the two growth conditions (natural climate vs death valley)?

E. californica has higher photosynthetic rates because they do not have hairs, therefore decreasing the albedo of the leaves. There was a greater difference between the two growth conditions because E. californica had no method of heat mitigation and therefore lost a greater percentage of max photosynthetic rate.

For E. farinosa (pubescence, lives in death valley), were there differences in maximum photosynthetic rate and quantum yield between the two growth conditions (mild stable climate vs death valley)?

The pubescence adaptation allows E. farinosa to maintain a temperature closer to their optimum in hot environments. Therefore there was a reduced difference in the photosynthetic rate depending on temperature.