Fall Leaf Colors

Illustration copyright Lauretta Jones

My friend Christine asked an interesting question recently: Why are autumn leaves so colorful one year, yet drab the next? Weather plays a role in the answer and so does the length of days. And the story is different for leaves that turn yellow and those that (sometimes) turn red.

Leaf colors are caused by pigments that also have other jobs. Familiar green chlorophyll is responsible for photosynthesis, turning carbon dioxide into sugar for the plant’s food. Pigments called carotenoids – which produce shades of yellow and orange – are also in the leaf’s cells, assisting and protecting the chlorophyll. In summer, the green of chlorophyll masks the yellow carotenoids. But as days grow shorter, the plant stops producing chlorophyll, and the yellow pigment is revealed.

The pigments that create the fiery reds of maples and deep wine of oaks are called anthocyanins, and they are only manufactured in the fall. This is where the weather has its influence. While the chlorophyll is waning, a succession of sunny days, cool (but not freezing) nights and moisture in the soil causes the plant to manufacture the most anthocyanins, and hence have the richest reds.

Why would a plant expend precious energy to create anthocyanins when it will soon drop its leaves? The red pigment must be doing something to earn its keep. This riddle is just recently being unravelled by scientists. Anthocyanins seem to act as sunscreen and antifreeze, and may ward off insect pests. All these actions enable the plant to send more nutrients to its roots for winter storage before the leaves drop off.

While this year has been rough on our fall foliage show, a walk through Angle Fly Preserve offers trees sporting a wide palette; with the dogwoods and red maples particularly enjoyable.

Bookmark the permalink.

Comments are closed.