Partly cloudy skies. A stray shower or thunderstorm is possible. Low near 75F. Winds SSE at 5 to 10 mph..

Partly cloudy skies. A stray shower or thunderstorm is possible. Low near 75F. Winds SSE at 5 to 10 mph.

Partly cloudy skies. A stray shower or thunderstorm is possible. Low near 75F. Winds SSE at 5 to 10 mph..

Partly cloudy skies. A stray shower or thunderstorm is possible. Low near 75F. Winds SSE at 5 to 10 mph.

In autumn the pigments in leaves begin to degrade. The destruction of chlorophyll progresses more rapidly than that of the carotenoids. As chlorophyll is destroyed, the green color of the leaf fades, leaving behind the yellow color of the carotenoids. In some trees, anthocyanins form in autumn, and these pigments cause the yellowing leaves to turn first orange and then red. Red maples, red oaks, and sumac produce anthocyanins in abundance and display the brightest reds and purples in the autumn landscape. In other trees, such as the beech, as the yellow carotenoids are destroyed, their color is replaced by the brown that results from the oxidation of tannins in the leaf.

In autumn the pigments in leaves begin to degrade. The destruction of chlorophyll progresses more rapidly than that of the carotenoids. As chlorophyll is destroyed, the green color of the leaf fades, leaving behind the yellow color of the carotenoids. In some trees, anthocyanins form in autumn, and these pigments cause the yellowing leaves to turn first orange and then red. Red maples, red oaks, and sumac produce anthocyanins in abundance and display the brightest reds and purples in the autumn landscape. In other trees, such as the beech, as the yellow carotenoids are destroyed, their color is replaced by the brown that results from the oxidation of tannins in the leaf.

Every autumn, we revel in the beauty of the fall colors the trees have to offer us. It’s another sign the autumn is truly here! But have we ever stopped to wonder why the trees respond this way?

First, what is the purpose of leaves? Leaves are nature’s food factories. Leaves start off with a green pigment due to a chemical called chlorophyll. Chlorophyll is responsible for the photosynthesis, the process where plants turn water and carbon dioxide into sugar. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a simple sugar plants use as food for energy and as a building block for growing.

There are several compounds responsible for the pigments in the leaves. Along with chlorophyll, there are also xanthophylls, carotenoids, anthocyanins, and tannins. Carotenoids pigments are always present in leaves, but the carotenoids have little effect on the color of the leaves as long as chlorophyll is present.

There are two types of carotenoids. Some are hydrocarbons, compounds that contain only carbon and hydrogen, such as beta carotene. Others, called xanthophylls, contain atoms in addition to carbon and hydrogen. The carotenoids function to protect the chlorophyll from a chemical process called oxidation and they also serve as accessory light absorbers. They absorb energy from light of different colors than that absorbed by chlorophyll, and the energy they absorb is transferred to chlorophyll.

Xanthophyll is responsible for the yellows of autumn leaves. Carotenoids also contribute orange colors. Beta carotene is one of the most common carotenoids in plants, and absorbs green and blue light strongly, reflecting red and yellow light and causing its orange appearance. Like the chlorophylls, carotenoids are also large molecules and are also contained in the chloroplasts.

Chlorophyll is not a very stable compound; bright sunlight causes it to decompose. To maintain the amount of chlorophyll needed in their leaves, the trees must continuously synthesize it, but this requires sunlight and warm temperatures. During the summer, chlorophyll is continuously broken down and regenerated in the leaves of trees. But once day length becomes shorter and temperatures begin to drop, the amount of chlorophyll in leaves begins to decline and the carotenoids and xanthophyll pigments become more visible.

A third class of pigments that occurs in leaves is the anthocyanins. Anthocyanins absorb blue, blue-green, and green light. Therefore, light reflected by leaves containing anthocyanins appears red. Unlike chlorophyll and the carotenoids, anthocyanins are not attached to cell membranes. They are made in the cell by an energy-consuming process initiated by light. As they are made, they are released into the cell sap.

Temperature, light, and water supply have great influence on the degree and duration of the fall colors. Warm, wet weather delays the disappearance of chlorophyll and the appearance of anthocyanins. Cool, dry weather favors the destruction of chlorophyll. Sunny weather promotes the formation of anthocyanins. So, the brightest autumn colors are dependent on what our weather conditions are 6-9 months before our leaves start to change. Time will tell what kind of vibrancy our leaves will be, but the rule of thumb is – the more vibrant the hue of their changing leaves, the healthier the tree.

Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, sex, age, religion, disability, or status as a veteran in any of its policies, practices or procedures. This includes but is not limited to admissions, employment, financial aid, and educational services.  References within this publication to any specific commercial product, process, or service by trade name, trademark, service mark, manufacturer, or otherwise does not constitute or imply endorsement by Oklahoma Cooperative Extension Service.

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