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Red autumn leaf12/29/2023 "Protection from bright light is important during this sensitive time, while senescing leaves are dismantling their photosynthetic apparatus." "Anthocyanins absorb wavelengths over a wide range of the solar spectrum, from UV-B to red," Renner said, allowing them to act as a kind of sunscreen. But why would more North American than European trees produce anthocyanins? A higher percentage of North American trees produced anthocyanins, the red or purplish colors. The latter turned out to be the typical case. "We wanted to assess whether related species have the same fall color-or whether instead North American species produce anthocyanins, while their European relatives do not," Renner said. The scientists combined their work with observations from the scientific literature and placed the color scores (red anthocyanin, yellow xanthophylls or non-colored green/brown) of some 1,532 species on a phylogenetic tree, which is a diagram that depicts the origin and evolution of groups of organisms. While their experiments initially did not focus on fall colors, Renner and Zohner noted and quantified the different percentages of American and European species that produce foliar anthocyanins, the pigments that are responsible for red or purple leaves. During the fall, trees growing at a particular latitude in eastern North America receive significantly more solar irradiation than do trees growing at the same latitude in Europe.Īnd in 2019, Renner and her collaborator Constantin Zohner figured out that North American trees, when grown in a common garden with European species, react differently to shorter days in the fall. Renner's experimental work with hundreds of species from throughout the Northern Hemisphere helps show why this is true. "Meehan had suggested that leaves might turn red 'under the influence perhaps of the American light," and European species, after many generations, might adapt to this light and then 'show their American colors.'" "He even mentioned the parameter that provides the most likely explanation," Renner said. "However, the very first paper to raise the question was written in 1881 by Thomas Meehan, a British-born botanist who had moved to Philadelphia. Renner, honorary professor of biology in Arts & Sciences at Washington University in St. "Botanists have thought about this question for a long time, but a plausible answer was only provided in 2019," said Susanne S.
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