What Makes Leaves Red in the Fall?

The leaves of many species of trees change color in the fall. While some leaves turn yellow, others turn red instead. The differences in the pigments present in the tree's leaves cause the different colors.

Types

• Chlorophyll is a pigment found in the chloroplasts of plant cells in leaves. It plays a vital role in photosynthesis as a molecule that absorbs sunlight. It's not the only pigment in plant cells, of course; plants also use pigments like carotene to absorb sunlight. Chlorophyll is so abundant, however, that during the summer its green color predominates, which is why tree leaves ordinarily appear green.

Function

• During the fall, deciduous trees cease producing chlorophyll as they prepare to lose their leaves before the coming winter. As the remaining chlorophyll breaks down, the leaf gradually loses its green color. The other pigments that were previously masked by the abundant chlorophyll now become the most prominent colors in the leaf.

Effects

• In some trees, carotene or other similar pigments predominate; the leaves of these trees turn yellow, since carotene absorbs blue and green light. In other trees, sugars stored in the sap react with certain proteins to form anthocyanins, pigments with a bright red color. The leaves of these trees turn red in the fall.