Autumn Leaves: Why Do they Change Color?

Autumn is here. For many people, Fall is their favorite season. Football games, chillier nights, sweater weather, bonfires, Halloween, Thanksgiving and the beautiful change in scenery all make it an amazing time of year. The most telling sign that Fall is here is the change in colors. The leaves begin to lose their natural green and instead show off a bevy of new colors. Different shades of red, yellow, orange, brown and sometimes a deep purple line the trees and gently fall to the ground. But what makes the leaves change so suddenly each year?
First, we have to understand why plants are green. Plants produce their own energy through a process called photosynthesis. This is the process the plant undergoes to produce usable energy. Plants take in sunlight, water and carbon dioxide to produce oxygen and glucose. Plants release the oxygen and use the glucose as a food source to continue to grow and continue its life. The chemical chlorophyll helps plants perform photosynthesis and chlorophyll is what gives plants their green pigmentation.
As the days get shorter and shorter in the fall season the trees “know” that winter is approaching. Winter does not have enough sunlight and water to produce photosynthesis so the trees go into a dormant stage where they shut down their systems and will use their stored energy attained over the summer to get through the winter. Because photosynthesis is no longer occurring the leaves and plants begin to lose their green color as chlorophyll is no longer present. As the leaves lose their green color we begin to see bits of yellow and orange. The leaves always had these colors present because of cartenoids, the same pigments that make carrots, bananas, and flowers yellow and orange, but were dominated by the green pigments. In the absence of the green chlorophyll we now see these yellow and orange colors.

We see red and purple because trees such as the maple have glucose in their leaves even after photosynthesis stops. Colder nights cause this glucose to turn the leaves bright red and purple colors and the pigments that cause these colors are caused by anthocyanins, the same pigments that apples, grapes, blueberries, etc. their exaggerated colors. And the brown color we see usually on oaks is made from waste from the tree.
Combine all these colors in close proximity and we have the beautiful combination of colors that we enjoy each Fall. Now when you rake them out of your yard you know why each leaf is the color that it is. Enjoy the season!




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