Wednesday, September 30, 2009

What Causes Fall Leaf Colors


You may have heard before what causes leaves to turn colors, but I thought it appropriate as leaves are turning already in the northern U.S. States, and starting in the mid-Atlantic. Here's a good reminder (from Livescience.com):
The green color of leaves during the spring and summer is a result of the presence of the pigment chlorophyll, which allows plants to capture sunlight and produce energy by the process of photosynthesis.
When the weather begins to turn cool in the fall, chlorophyll, which is sensitive to the cold, stops being produced. As the green fades, yellow and orange pigments called carotenoids (also responsible for the orange color of carrots) take over. These pigments were always present in the background of the leaves' color, but can finally shine through as the green diminishes.
The red color comes from anthocyanins, which unlike carotenoids are produced only in the fall. These red pigments act as sunscreen for the trees by blocking out harmful radiation and preventing overexposure to light. They also act as an antifreeze, preventing leaf cells from freezing easily in the autumn chill. Some scientists have even suggested that the red colors ward off pests.

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