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Autumn Color

November 22, 2007

Fall colors come in several shades. But why the different colors?


Autumn’s red leaves explained. I’m Bob Hirshon and this is Science Update.

In many parts of the country, fall brings spectacular displays of foliage. But until now, scientists have wondered why some trees of the same species turn yellow and orange in autumn while others turn red. Biologist Emily Habinck of the University of North Carolina at Charlotte recently found that leaves are more likely to turn red in nutrient-poor soils than in nutrient-rich ones. She says the red pigment anthocyanin is costly for leaves to produce. But it may protect trees against the nutrient-sapping effects of the sun in cold weather.

EMILY HABINCK (University of North Carolina at Charlotte):
In nutrient-poor areas, the trees are going to conserve as many nutrients as possible, so they’re going to synthesize more anthocyanins to help the recycling of nutrients back into the tree.

This may explain why nutrient-rich bottomland forests have few red-leaved trees in the fall. I’m Bob Hirshon, for AAAS, the science society.