Red or Yellow Leaf Color Determined by Soil

Oct. 25, 2007 -- The hues of an autumnal hillside may owe as much to the soils under the trees as the trees themselves, according to a student researcher at North Carolina State University.

A preliminary study of fall leaf colors and the soils under sweet gum and red maple trees in hilly North Carolina show a significant nutrient difference that matches autumn tree color patterns.

The discovery matches the expectation of other researchers looking into why trees of the same species turn red with the pigment anthocyanin in some places and yellow without the pigment in others.

"Through the years biologists have debated whether it served a function," said soil researcher Martha Eppes of the University of North Carolina.

It was Eppes' student Emily Habinck who conducted the new work, which will be presented on Oct. 29 at the meeting of the Geological Society of America in Denver.

Habinck conducted an autumn inventory and laboratory leaf analyses of red maples and sweetgum trees along transects from a low-lying floodplain up to an adjacent valley divide in the UNC-Charlotte nature preserve in Charlotte, N.C. She confirmed that the trees were redder on steeper slopes and at the top of the divide when compared to the floodplains.

Likewise, Habinck found that the colors matched different soils types: the richer lowland soils corresponded to more yellow leaves and poorer highland soils correlated to redder leaves.