Curiosities: Why do leaves change colors in autumn?

By Eddy Montilla.


This is one of the few moments when the reverse can give you a better answer and lead you to the place you want to go faster. Then, let’s see first why most leaves are green in fall. Leaves are green during the growing season thanks to chlorophyll, a green substance that not only provides the plants with that color, but helps them grow and keeps them alive by absorbing light from the sun. We eat to live; plants do the same too, but they neither have a mouth nor can take carbohydrates from cereal, potatoes, etc., as we do. Instead, green plants use a chemical process that turns carbon dioxide and water into food (carbohydrates) by using energy coming from sunlight. This process is called photosynthesis and it would not be possible without the chlorophyll we mentioned before and, of course, sunlight.

Green chlorophyll coexists with red, yellow and orange pigment molecules called carotenoids in a leaf. In autumn, because of the temperature and, especially, because of the much lower proportion of sunlight, the photosynthesis process does not continue, the green chlorophyll fails and the red, yellow and orange carotenoids emerge giving the leaves the beautiful color we enjoy in that season. Luckily, not all trees turn their green leaves into red, yellow and orange. Broad-leaved plants like those famous Canadian sugar maples or Japanese ginkgo are more sensitive to change while evergreens can protect their leaves better.

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