why do trees leaves turn different colors in the fall
Why Do Leaves Change Color in Autumn? We all enjoy the colors of autumn leaves. The changing fall foliage never fails to surprise and delight us. Did you ever wonder how and why a fall leaf changes color? Why a maple leaf turns bright red? Where do the yellows and oranges come from? To answer those questions, we first have to understand what leaves are and what they do. Find maps, dates, and best scenic drives for fall colors
Leaves are nature's food factories. 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 oxygen and glucose.
Oxygen is a gas in the air that we need to breathe. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into oxygen and sugar is called photosynthesis. That means "putting together with light. " A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their green color. As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter. During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer.
They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green chlorophyll. The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red color.
The brown color of trees like oaks is made from wastes left in the leaves. It is the combination of all these things that make the beautiful fall foliage colors we enjoy each year. Plants are busy growing all summer long. But how do they survive the dark, dry days of winter? How Do Plants Prepare for Winter? Plants are busy growing all summer long. But how do they survive the dark, dry days of winter? Leaves are loaded with chlorophyll, which makes them green. But all green plants also carry a set of chemicals called carotenoids. On their own, these look yellow or orangeБcarotenoids give color to corn and carrots, for exampleБbut theyБre invisible beneath the chlorophyllic green of a leaf for most of the year.
In the fall, when the leaves are nearing the end of their life cycle, the chlorophyll breaks down, and the yellow-orange is revealed. БThe color of a leaf is subtractive, like crayons on a piece of paper,Б says David Lee, formerly of Florida International University, who has studied leaf color since 1973. Most trees have evolved to produce a different set of chemicals, called anthocyanins, when itБs bright and cold in autumn. These have a reddish tint and are responsible for the color of a blueberry. TheyБre also sometimes made in newly sprouting leaves, which explains their sometimes reddish tint.
Where chlorophyll and anthocyanins coexist, the color of a leaf may run to bronze, as in ash trees. At high enough concentrations, anthocyanins will make a leaf look almost purple, as in Japanese maples. More drab autumn colors form as leaves really die and complete the breakdown of the chloroplasts. When theyБre all dried out, the pigments link up together into what Lee calls a Бbrownish gunk. Б Have a burning science question you'd like to see answered in our FYI section? Email it to. _This article originally appeared in the November 2013 issue of _Popular Science.
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