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Four for Fall: What makes those colorful hues?

Written by Melissa Gaskill.


Melissa Gaskill shares the scoop on fall’s transformation. See her story on four autumn escapes in the November 2010 issue of Texas Highways.

How does nature create fall’s brilliant hues? With light, temperature, pigment, and sugar. Tree leaves look green thanks to a substance called chlorophyll. Throughout the sunny days of summer, leaves use it to turn sunlight, water, and carbon dioxide into glucose, or high-energy sugar. In fall, when days grow shorter and temperatures drop, trees take this as a signal to prepare for winter. A special layer of cells at the base of each leaf that carried water into the leaf and food out of it all summer now closes off. Without water, chlorophyll begins to break down. When it’s gone, we can see other pigments present in the leaves; orange carotene, yellow xanthophyll, and red and purple anthocyanin. Leaves that don’t have these present simply turn brown from tannin, a waste product. Eventually, every brown or flame-colored leaf drops to the ground, and without its moisture-filled leaves, the tree stands ready to face winter’s cold. Evergreens, which don’t drop their leaves, have hardier foliage, often additionally protected by a waxy coating.

Since nature never wastes anything, fallen leaves return nutrients to the soil and become food for many organisms, including, perhaps, the trees from which they fell.

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