With the first day of fall behind us and the crisp fall air blowing through the trees, one thing is for sure- the leaves will begin to start changing color and beginning to fall off the trees. Sure nothing is better than racking all of the leaves up just so you can jump in them or going to the apple orchard to pick out your favorite apples to make your delectable dish. But the real question is do trees really “change” color or do they go back to their color? Why do leaves change colors during each season?
The answer is really the growth process. As summer comes to an end and the days begin to get shorter and the nights begin to get longer, plants become sensitive to the length of the dark period each day. When the nights are long enough and the threshold value is reached, the cells near the juncture of the leaf and the stem divide rapidly, but they do not expand. The abscission layer is a corky layer of cells that begin to block the flow of minerals from the roots to the leaves. However, this process starts to begin at the same time every year whether the temperatures are warm or cool.
Chlorophyll is replaced constantly in the leaves of plants throughout the growing season. Chlorophyll breaks down the exposure to light just like leaving a colored shirt out in the sun- it begins to fade. The leaves must manufacture new chlorophyll to replace what is lost along the way. In the fall, when the connection between the leaf and the plant begins to block off, the production of chlorophyll slows and stops and may even disappear completely.
During this process is when the autumn colors are revealed. Chlorophyll normally masks the yellow pigments and orange pigments, which then become visible when the green chlorophyll is gone. These colors are very visible throughout the growing season. However, red and purple pigments can appear and come from anthocyanins, which are manufactured from the sugars that are trapped in the leaf.