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The Science of Changing Leaves

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Is red a defensive color? (11/22/18 – El Dorado Hills) John Poimiroo

A couple of years ago, Smithsonian.com posted a time-lapse video of leaves transforming from chlorophyll-filled green to tones of yellow, red and brown. The video was accompanied by an article explaining how leaves change color and some misconceptions about the process.

The video was created by Owen Reiser, a mathematics and biology student at Southern Illinois University Edwardsville. Reiser, Smithsonian.com reports, took 6,000 photos of leaves to weave the video together.

Leaves that change due to the loss of chlorophyl as a result of shorter days and fewer nutrients tend to turn orange or yellow. Though David Lee, Professor Emeritus of biological sciences at Florida International University and author of Nature’s Palette, The Science of Plant Color, says that many yellow and orange leaves do not change the same way as red leaves.

Lee states in a Smithsonian.com article that the breakdown of chlorophyll in leaves does reveal yellow and orange (carotenoids) hidden beneath, but that red (anthocyanin) pigments are produced within the leaves as they die.

There are two thoughts as to why this happens. One is that the red color is a defensive measure to make the plants appear unhealthy as the leaf dies, protecting the tree from plant-eating bugs and animals which are conditioned not to eat red foliage.

The other thought is that red is a form of photo protection. Horticulturist Bill Hoch, Smithsonian.com reports, believes red’s wavelength helps shield the leaf by absorbing excess light allowing the plant to more efficiently remove nitrogen from the proteins that are breaking down and send that nutrient back to tree limbs and roots, saving as much of it as possible before winter.

Whatever the cause, the result is spectacular and less than a month away from being seen in California.

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