By JAMES L. CUMMINS
Special to The Sun-Sentinel
Everyone knows that when the leaves change colors, fall is in the air. Kids in elementary school are told the basics of how this happens, but how much do most people know about the whole process?
Leaves are important to the health of the tree. Trees take water from the ground through their roots and absorb carbon dioxide from the air. Sunlight is then used to turn the water and carbon dioxide into oxygen and carbohydrates. This process is known as photosynthesis. The resulting oxygen is released from the tree and used by people and other living organisms; oxygen is crucial to our survival. The resulting carbohydrates, such as sugar and starches, are used by the tree as food for energy and as a building block for growth.
Leaf color comes from pigments. The three pigments responsible for leaf color are: chlorophyll, carotenoid and anthocyanin. These pigments are naturally produced by leaf cells and each is responsible for different colors.
Of these three pigments, chlorophyll is the most important in the life of the leaf and the tree. Chlorophyll is responsible for the green shades of leaves and is vital in the process of photosynthesis. Without chlorophyll, trees would not be able to use sunlight to produce its food. During longer daylight hours of spring and summer, the leaves absorb sunlight to transform carbon dioxide and the water taken in from the roots into carbohydrates that are essential to life of the tree.
Carotenoids are responsible for the bright yellows, oranges and shades of brown that we see when fall rolls around. Interestingly, while chlorophyll and the green color it gives the leaves is most prominent during spring and summer, carotenoids are also present but remain hidden by the overwhelming amount of chlorophyll.
In the fall, when our daylight hours become shorter and temperatures change, the leaves stop their food-making process. Chlorophyll starts to break down, which causes the green color to give way to the yellows and oranges that have been present all along. Other chemical changes sometimes occur when anthocyanin is more abundant. It is responsible for the red and purplish tints found in some leaves.
Of course, anyone that has taken notice of the brilliant colors of fall has also noticed that there are also those trees that never lose their green color. For instance, most of the conifers — spruces, firs, hemlocks, cedars and pines, among others — are considered to be evergreens. This is because their leaves, or needles, are covered with a heavy wax coating and fluids inside the cells contain substances that help it to resist freezing.
While this is a brief summation of the color-changing process in leaves, a deeper look into all that goes into the growth of a tree is truly fascinating. When you stop to enjoy the beautiful sights and brilliant colors of fall, consider the awesome process the tree undergoes to ensure its growth and vitality.
James L. Cummins is executive director of Wildlife Mississippi, a nonprofit, conservation organization founded to conserve, restore and enhance fish, wildlife and plant resources.
