Leaves' Fall Colors Have "Dirty" Secret, Study Finds

Richard A. Lovett
for National Geographic News
October 30, 2007

New Englanders are blaming this year's lackluster fall-color season on drought, but if you don't like the colors in your own backyard, you might blame the dirt, a new study says.

In an undergraduate research project, Emily Habinck, who has since graduated from the University of North Carolina at Charlotte, found that autumn leaf color is related to the richness of the soil.

She determined that on a North Carolina floodplain that was rich in nitrate—a nitrogen-containing nutrient—yellow-leafed trees dominated. But in the poorer soils of the hillside behind it, there were more reds.

(See wallpaper photos of autumn leaves.)

Even among the trees that typically bear red leaves no matter the conditions, poorer soils made for redder hues.

Habinck based her study on her faculty advisor's observation that floodplain trees tended to be yellow and that soil nutrients might have something to do with it.

While Habinck was at work on the project, William Hoch, a plant physiologist at Montana State University, wrote a paper suggesting an additional link between the red-leaf pigment anthocyanin and autumn sunlight.

"It wasn't until I read his paper that it became a full story," Habinck said.

Leaf Protection

Leaves turn color in the fall as trees start shutting down their energy production and withdrawing nutrients into their roots.

(Read: "Why Do Fall Leaves Change Color?" [October 8, 2004].)

"[The tree] pulls as many of these in as it can, then tries to drop just a skeleton of a leaf when it's done," Hoch said in a telephone interview.

Continued on Next Page >>


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