Why do leaves change color?

While the seasons are shifting, the Columbia Gorge has turned into a spectrum of colors that is
sure to impress anyone with an eye for beauty. Spending much of my time outside I have been able to watch the sources of this display slowly transform into their winter state. The question that has remained on the minds of many, while being captivated by the ambiance of leaves turning shades of red, continues to be, “Why do leaves change color?”

Many of us may remember learning that chlorophyll is responsible for providing the color green to leaves on a tree. Chloropyll is also the most important pigment in plants because without it, they would not be able to use the sunlight to produce food for themselves. However, leaves may also have two other pigments which include carotenoid and anthocyanin. Carotenoid is a popular pigment that causes yellow, orange, and brown. Corn, carrots, and bananas are a few of the familiar fruits and vegetables that are colored by carotenoid. Anthocyanin is a less common pigment that adds the color red to plants. Red apples, cherries, and strawberries are familiar fruits that receive their color from anthocyanin.

Chloropyll and carotenoid are found within the cells of leaves all the time. The carotenoid is covered by the chloropyhll and therefore the leaves are green rather than yellow or orange.  Anthocyanins are typically only produced in the fall and only under certain conditions. Not all plants are able to produce anthocyanin. The plants that do produce anthocyanin are rewarded for their efforts.

As the earth rotates around the sun and autumn approaches, deciduous trees begin to prepare for winter. As the leaves get less and less sunlight they produce less and less chloropyll. Eventually the chlorophyll production will stop altogether allowing the carotenoid to show off  it’s warm yellows, bright oranges, and distinct browns. Temperature and cloud cover are the biggest factors in anthocyanin production. When there are a number of warm sunny days and cool but not freezing nights, you’re sure to see a rainbow of reds on trees. The sunny days allow the plant to produce sugar, however, the cool nights reduce the flow of the sugar from the leaf back into the branches. This is when the plant, if capable, will produce anthocyanin which helps in the recovery of nutrients before the leaf falls. Anthocyanin is a hero, and very enjoyable to witness!


All information from (and to explore further): http://dnr.wi.gov/org/caer/ce/eek/veg/trees/treestruecolor.htm

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