![]() During this process, explains William Hoch, a plant physiologist at the University of Wisconsin in Madison, sunlight can easily destroy the leafs tissues. But in autumn, the tree begins to break these tissues down in order to reabsorb their nutrients for the winter. During the summer months, a leafs photosynthetic tissues can handle most of the radiation they receive from the sun. The red pigment, both groups claim, may act as a sunscreen. In the past months, two independent groups may have finally shed some light on the mystery. "Thats the reason its aroused so much curiosity." ![]() "Its an enormous metabolic input into a leaf thats just about to fall off the tree," says Kevin Gould, a plant physiologist at the University of Auckland in New Zealand. And so researchers couldnt figure out why a tree would sacrifice some of its much needed sugars for a dying leaf. The pigment production uses valuable sugars that could help the tree survive the winter months. ![]() Researchers learned that during the autumn season certain tree species actually manufacture red pigment in their leaves. This theory held sway for more than half a century, but in the 1970s, researchers found that one shade stood out from the crowd: red. The green pigment filled the leaves in summer, but come fall, that color drainedleaving behind brilliant reds, yellows and oranges. Leaves, they said, were filled with several different pigments. The truth behind falls splendor, it turns out, may be more complex than any single hypothesis can explain.Īt the turn of the 20th century, most naturalists believed that nutrient recycling caused the autumn colors. But a host of competing theories make very different claimsthat the tint is a bug repellent, an animal attractor or a form of frost protection. The research, done by two independent collaborations, indicates that red pigments are a sunscreen that protects leaves while the tree reabsorbs their nutrients. Thats because recent research on autumn leaves has fueled a debate about why trees turn crimson. Although most people find the warm hues of October foliage soothing, the colors have some biologists seeing red.
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