Autumn colors all about chemistry
The Lowcountry is known for gorgeous beaches, historic architecture, sweeping marshes and grand trees.
However, when “leaf peepers” go in search of trees displaying spectacular fall color, they often head to the Upstate and even farther north.
At higher elevations, hillsides burst with masses of gold, red, orange and plum-hued fall finery.
In the Lowcountry, crystal blue skies over olive-hued marshes teeming with dragonflies are the first sign that fall has begun to slide downstate.
As the nights cool and the days shorten, deciduous trees along the coast put on a more subtle show than their Upstate cohorts, revealing their fall splendor in their own sweet time.
Autumn brings beautiful changes in leaf color, yet we rarely think about the processes that contribute to the production of such amazing hues.
Many environmental factors are part of the chemical and physical changes that bring about fall leaf color in deciduous trees and shrubs. While appearing quite complex, fall leaf-color change is both predictable and fascinating.
Pigments in plant cells dictate leaf colors. In spring and summer, chlorophyll is the dominant pigment responsible for green leaves.
Essential to photosynthesis, chlorophyll is a key ingredient in the chemical conversion of sunlight into carbohydrates that are used for plant growth and development.
This function makes chlorophyll extremely valuable to plants and the process that leads to leaf drop and winter dormancy is genetically designed to preserve this life sustaining material and conserve the energy required to produce it.
Environmental cues such as rainfall, shorter days and lower nighttime temperatures signal abscission cells at the leaf petiole (where leaves attach to branches) that winter is coming.
These cells begin to thicken and obstruct the flow of water from tree roots out to the leaves. Simultaneously, important nutrients such as nitrogen, a key part of chlorophyll production, are absorbed into buds and branches and stored until the next favorable growing season.
Less water in the leaves causes chlorophyll to break down, thus shutting down growth for the winter.
As the abscission cells at the leaf bases completely close off and force leaves to drop to the ground, chlorophyll breaks down revealing other pigments that were present all along, but obscured by the green of chlorophyll.
Four main groups of pigments are responsible for the colors found in plants, and even some animals that eat plants (think flamingos and chickens that are fed marigolds for golden skin). These pigments are revealed by disappearing chlorophyll in leaf tissues and the rainbow of fall colors is unveiled.
Dr. Kim D. Coder at the University of Georgia’s Warnell School of Forest Resources divides the color pigments produced by trees into three categories “watercolors, oil paints and earth tones” to describe their intensity and longevity in fall leaf color.
Anthocyanin pigments produce red, pink, purple and blue hues in nature and are described as “watercolors” because they mix with water in plant cells and therefore don’t stick around long in the life of plants.
Blueberries, cranberries and apples are just a few examples of anthocyanin’s range of colors in the wider plant world. Red maples, red oaks, and sumac are good examples of anthocyanin’s short -lived but breathtaking fall colors.
Carotenoid pigments produce long lasting “oil paints” that color our world red, orange and yellow. Sycamores, hickories, and poplars are all examples of these long lasting pigments found in fall leaves.
Tannins are “water soluble colorants that produce medium and dark browns” according to Dr. Coder. These compounds are responsible for the earth-tone tans and browns that are part of the bronzed landscape of fall. American beech, black walnut and dawn redwood are notable expressions of tannins in the fall landscape.
The fourth groups of pigments are the betalins that produce the red color found in beets. Most of the trees that have this pigment are found in the Mediterranean region and are salt and drought tolerant. Betalins are rarely seen in Eastern U.S. forest trees, but are sometimes seen in forest edges and understory plants.
For a fascinating read on the science behind fall color, check out Dr. Coder’s “Primer On Autumn Tree Leaf Colors.”
The paper can be found online at http://bit.ly/17g0X8r.
My favorite quote from this in-depth read is “The chemistry of tree life can be colorful!”
Arbor Day tree sale
The Tri-County Master Gardener Association and Clemson Extension announce the first Arbor Day Tree Sale Fundraiser.
Plants for sale include fruit and ornamental shade trees and shrubs. These must be preordered by Nov. 18.
A printable order form is available at http://bit.ly/19zVvDj.
Trees will be available for pick up from 9 a.m. to 6 p.m. Dec. 6 (Arbor Day) at the Clemson University Coastal Research & Education Center at 2865 Savannah Highway.
For more information, contact Derrick Phinney at 563-0135.