The signs of changing seasons are all around us, and the most obvious of all can be found on deciduous trees throughout much of the country. Did you ever wonder why some leaves turn yellow while others turn red each fall? Or perhaps you’re curious why some leaves maintain their color before falling to the ground each year.
|
|
|
|
Well, leaves produce food for the plant. After a plant takes up water and nutrients from the ground through the root system and take in carbon dioxide gas through the leaves from the air, the plant will use sunlight to turn these elements into glucose. Plants will use glucose, a form of sugar, as food for energy to grow. This process is called photosynthesis. Chlorophyll helps make photosynthesis occur and also gives the plant its green color. As the days get shorter during the fall, the photosynthesis process slows down and the plant prepares for the winter. Plants will shut down the food producing leaves and begin to live off the stored energy that was produced during the summer. Since many plants are “day length” regulated, plants located in warmer climates will lose their leaves even though air temperatures are comparable to summer temperatures for cooler climates. This also explains why leaves in the shaded center of a plant will turn colors before leaves exposed to the sunlight.
As plants stop using the leaves to produce food, the chlorophyll will begin to disappear from the leaves. As the chlorophyll disappears, the leaves’ true colors of yellow and orange begin to appear. This is why we see the same colors in the leaves of plants that are stressed during the summer from pest damage or cultural damage. Leaves that appear red or purpose in the fall (maples) are caused from glucose being trapped within the leaf and photosynthesis stops. Sunlight and cool temperatures will turn the glucose into the bright reds and purples. Meanwhile, brown leaves result when waste products from photosynthesis are trapped within the leaves (common in oaks).
Over time, a cuticle barrier forms at the base of the leaf petiole to prevent any moisture loss during the winter. Once this barrier forms completely, the leaf drops off the plant.
The authors are part of LESCO's Tech Services Department. They can be reached at fromthefield@gie.net or at 800/321-5325 ext. 3150 to answer technical questions.