The Color of Autumn

In his book, Life’s Edge, Carl Zimmer explains why the leaves of some trees change color in autumn. Chlorophyll is what gives leave their green color – it is needed for photosynthesis, the green color is incidental. In turn, chlorophyll is made of 4 atoms of nitrogen. Therein lies the answer.

 

If the tree just dropped the leaves at autumn, it would have to spend a lot of effort later to first find nitrogen in the soil, then pump it up from the roots to the branches to make the chlorophyll for the new leaves.

“Instead, the tree spent the autumn carefully dismantling its chlorophyll into molecular parts, which it moves down little tunnels from the leaves into the branches. There the parts would spend the winter in safekeeping, ready to be quickly moved into new leaves in the spring and reassembled into fresh chlorophyll.”

 

This is a smart strategy, but it creates a new problem. Because chlorophyll serves another purpose – it acts as a sunscreen protecting the proteins and genes of the tree from high energy sunlight. The solution to this new problem? The tree produces a red pigment called anthocyanin which enters the leaves. This red pigment protects the tree from sun damage while the chlorophyll is being dismantled. And yes, it gives the leaves the red color of autumn.