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Red or Yellow Leaf Color Determined by Soil

Larry O'Hanlon, Discovery News

"It's very clear that there's a correlation," said plant physiologist Bill Hoch of Montana State University in Bozeman. What's more, it matches what he has discovered about the function of that stunning red anthocyanin.

Experiments make a pretty strong case for anthocyanin serving as a protective pigment that helps trees in nutrient-poor or stressed places to maximize the nutrients they can draw from the leaves before they are dropped to the ground, Hoch told Discovery News.

"They pull as many of the nutrients back into the plants as possible," said Hoch.

The red pigment protects any remaining green food-making chloroplasts in the leaves from damage. This is especially valuable for trees in nutrient-poor soils or stressful situations because this "photo-protection" allows the leaves to keep making sugars in their leaves longer.

This, in turn, is vital for pulling nutrients out of the leaves because the only way the nutrients can be extracted from leaf to trunk is by hitching a ride on the trunk-bound sugars.

The bottom line, Hoch explained, is that the longer photosynthesis can continue on an autumnal, coloring leaf, the more nutrients can be drawn out of it for re-use in the spring. So where every drop of nutrient counts the most -- like perhaps on some nutrient-poor hillsides of North Carolina -- red is the color of autumn.

Related Links:

U.S. Geological Survey

Geological Society of America

Wikipedia: Anthocyanin

North Carolina State University