How the leaves change on the trees
Published 10:33 pm Friday, October 28, 2016
By Ty Torrance
This fall, when the leaves begin to color and fall, I want you to know what you are seeing. The show of fall leaf color is an amazing thing, and you may be surprised to know how it happens. Think about it, a green leaf will turn to one of many vibrant colors before it drops to the ground. Why do the leaves put on that color? Is there a purpose?
The process of the color change bears some explanation. There are many pigments present in a leaf all year long, but in most cases we only see the green color expressed. The leaf doesn’t turn red, yellow, or brown due to some chemical appearing in the leaf. It actually makes the change because of a chemical disappearing from the leaf.
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A leaf contains a green compound known as chlorophyll. You may know chlorophyll as the green pigment in chloroplast structures that capture light and convert it to food for the plant. The green color is actually covering up the reds, oranges, and yellows that we see in the fall. All of the colors in a leaf can be tied to a pigment compound. Anthocyanins express reds and purples, Xythophylls express yellows, and Carotenoids express shades of orange. When the Anthocyanins and Carotenoids combine, deep oranges, bright reds, and bronze colors can develop. If you think about all of the possible combinations and concentrations of these pigments, you can imagine hundreds of different shades of color in the fall leaves.
There are a number of factors that can effect leaf drop in the fall; such as moisture levels, stress levels, temperatures, and day length. The most common association people have with leaf coloring and drop is cooler temperatures. While temperatures do play a role in the process, leaf drop is actually more closely associated with day length.
When the day length shortens and cooler temperatures are experienced the leaf slows down its production of chlorophyll. As the leaf shuts down, chlorophyll is produced in smaller amounts until it finally ceases production. With chlorophyll out of the way, other pigments in the leaf are expressed which gives the fall color.
In fact, if anything affects the manufacturing of chlorophyll in the plant leaf, the colors we associate with fall can also be seen in the summer. You may have seen a limb of your tree turn red or yellow while the rest of the tree remains green. Something has interfered with the chlorophyll production causing the other pigments in the leaf to be expressed. If this happens in the growing season, the pigments that are expressed can sometimes be tied to specific nutrient deficiencies. For example, if we see purpling in corn it can be associated to phosphorus deficiency.
So, now you know more than you ever wanted about fall color. Hope I haven’t ruined it for you. For those of you planning a trip to the North Georgia Mountains because you are really excited about this phenomenon, you can even find a report on the North Georgia fall color progress if you search the USDA website.
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