[Photosynthesis] 5.How does leaf position on a tree affect photosynthesis?

Plants we see out in the wild display evolutionary adaptions to growth in bright sunshine or shade. Leaves of tree often show developmental adaptions to different conditions. Leaves on the exterior of the canopy are refered to as 'Sun' leaves, and they develop under conditions of direct sunlight. Leaves within the crown of the tree are adapted to the shade created by surrounding leaves thus refering them as 'Shade' leaves. These adaptions include differences in leaf anatomy, metabolism (such as photosynthesis) and shape.

Plants are usually adapted to growth in direct sunlight or shaded conditions. Similar differences are observed among the leaves of large trees; those leaves that develop under the shade of other leaves are anatomically and metabolically different from those that grow on exposed canopy surfaces.

Shade-type leaves typically are thinner, have more surface area, and contain more chlorophyll than those of sun leaves. As a result, shade-leaves (curve B) often are more efficient in harvesting sunlight at low light levels; remember, the slope of the line observed under low light conditions is a measure of photosynthetic efficiency. However, sun-leaves (curve A) display a higher light saturation point and maximum rate of photosynthesis.