Red fall color linked to poor soil

The splendor of fall color may have as much to do with soil composition as with trees themselves.

As the season turns, cooler temperatures and shorter days inhibit production of chlorophyll, the molecule that enables plants to absorb energy from the sun and gives leaves their green color. As the chlorophyll dwindles, the yellow pigments that it masked become apparent to the eye.

But some trees also appear to produce more red pigments, known as anthocyanins, in their leaves when their roots are in soil that is relatively low in nitrogen and other nutrients, according to research presented Monday at the Geological Society of America's annual meeting in Denver.

That finding was made by researcher Emily Habinck, then an undergraduate at the University of North Carolina, who surveyed and analyzed the fall foliage of sweet gum and red maple trees in a nature preserve in Charlotte.

Scientists believe anthocyanins and the red color they produce protect the leaves, delaying their decay and allowing the tree to harvest more nutrients from the leaves before winter. Trees in poor soil therefore would be expected to produce more red leaves.

"For species that don't turn red, they are probably adapted to higher nutrient conditions," said Habinck, now an interpretive ranger at McDowell Mountain Regional Park near Phoenix.