FunNature & AnimalWhy do the leaves change color in autumn?

Why do the leaves change color in autumn?

In autumn, the deciduous forests around the planet turn ocher, orange, reddish and even purple. This fact makes them visually suggestive, magical places for a short period of time. The forest prepares to endure the winter. By shedding them, deciduous trees enter a state of numbness that will allow them to survive the cold with minimal water and energy expenditure. But, what is the reason for the wide range of colors that stains our forests? On this occasion, biochemistry provides us with the solution to the mystery.

The leaves of the trees contain many types of pigments or biochromes, substances capable of selective absorption of light of specific wavelengths. Its main function in vegetables is to contribute to the photosynthesis process, helping to capture as much light energy as possible for the creation of organic matter. As a curiosity, animals also have different types of pigments with multiple functions, from luminescent ones, such as luciferin, to those that protect our skin from solar radiation, such as melanin.

The most numerous pigment in plants is chlorophyll. It is the one that gives them the green color. This pigment needs heat and light to be synthesized. As these two factors decrease with the arrival of autumn, their production decreases and these molecules begin to degrade.

By decreasing the amount of chlorophyll, pigments such as carotenoids and flavonoids, always present in the leaves, but hidden by chlorophyll, come to light. These compounds contribute to the yellowing of the leaves. A subclass of carotenoids, xanthophylls, like luteins, are also those that color the yellow of egg yolks. Other carotenoids, such as beta-carotenes, responsible for absorbing wavelengths of green and blue, give an orange color to leaves, in addition to carrots. Although carotenoids begin to degrade at the same time as chlorophylls, they do so more slowly, even in fallen leaves large amounts of these pigments can be found.

Finally, anthocyanins, which provide red, purple or blue color to leaves, flowers and fruits, such as blackberries or blueberries. Unlike the previous ones, they are pigments that begin to be synthesized in early autumn, activated by the high concentration of sugars in the leaves and sunlight. Its biological function is not yet clear and has generated much debate in the scientific community. Some of the suggested hypotheses are: protection of chloroplasts from the adverse effects of excess light; the attenuation of UV-B radiation; and an antioxidant activity. However, the role of these pigments varies greatly between different plant species and in fact, none of these hypotheses adequately explains the variation in the spatial and temporal patterns of anthocyanin production.

Now that you can name the different biochemical compounds that you see in the leaves, it’s time to enjoy a good autumn walk, a time that lasts too little.

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