Why autumn leaves change color
Every fall, Mother Nature puts on a gorgeous show across much of America, but how does she manage all those vivid colors?
Thursday, October 21, 2010 - 14:59
TRUE COLORS: As winter approaches, leaves lose their summer green, giving other pigments a chance to shine. (Photo: joiseyshowaa/Flickr)
Ever wonder why that sugar maple in your back yard turns scarlet in autumn? Or why oak leaves turn russet and brown? You might be surprised to learn that the answer has to do with the way in which trees eat.
The leaves on a tree are like a million greedy fingers, all stretched out and looking for some lunch. They reach out, gathering sunlight and carbon dioxide from the surrounding air, combine this with water taken up through the tree's roots, and then they go to work, making the nutrients the tree needs to survive. But how can those little leaves keep a whole tree well fed?
The answer lies in the power of numbers. Each tree has thousands of leaves, each leaf is made of millions of cells, and each cell contains a number of chloroplasts, the tiny energy factories where the food is made. The key to the chloroplasts' power is a green pigment called chlorophyll which plays a key role in the conversion of raw resources — water, light and carbon dioxide — into foods like starch and sugar.
So what does this have to do with autumn colors? Green chlorophyll, it turns out, is not the only pigment in leaves; they also contain yellow xanthophyll and orange carotenes. During the growing season, there's simply so much green chlorophyll that it's all we can see, but during the winter, when light and water become scare, trees often go into a period of rest. They slow their growth and sort of hunker down, living off food that they stored up over the summer. The chloroplasts shut down and the chlorophyll inside them begins to break down. As the chlorophyll disappears, we begin to see the other pigments in the leaves; golden yellows and warm shades of orange shine through.
In some trees, the breakdown of summer products also causes the formation of a new pigment called anthocyanin which gives the leaves a brilliant red color. In others, like oaks, leftover byproducts give the leaves a rich russet-brown color.
But pigments aren't the whole story; weather also plays a role. Cold temperatures can aid in the formation of anthocyanin leading to redder reds and more vivid purples. If gets too cold, however, those same colors will be dampened. So pick a nice, cool autumn day, take your camera and a friend, and head out to enjoy one of nature's most spectacular shows.
Photos: sigusr0/Flickr, ingridtaylar/Flickr, nicolasconnault/Flickr
You might also like: