A Change of Seasons

by Jon Burch Photography

Title

A Change of Seasons

Artist

Jon Burch Photography

Medium

Photograph - Digital Capture And Enhancement

Description

Colorful foliage during a mid-September Rocky Mountain autumn dazzles the eye. But why?

When leaves appear green, it is because they contain an abundance of chlorophyll. There is so much chlorophyll in an active leaf that the green masks other pigment colors. Light regulates chlorophyll production, so as autumn days grow shorter, less chlorophyll is produced. The decomposition rate of chlorophyll remains constant, so the green color starts to fade from leaves.

At the same time, surging sugar concentrations cause increased production of anthocyanin pigments. Leaves containing primarily anthocyanins appear red. Carotenoids are another class of pigments found in some leaves. The carotenoid production is not dependent on light, so levels aren't diminished by shortened days. Carotenoids can be orange, yellow, or red, but most of these pigments found in leaves are yellow. Leaves with good amounts of both anthocyanins and carotenoids will appear orange.

Leaves with carotenoids but little or no anthocyanin will appear yellow. In the absence of these pigments, other plant chemicals also can affect leaf color including tannins, which are responsible for the brownish color of some oak leaves.

Temperature affects the rate of chemical reactions, including those in leaves, and plays an important part in leaf color. However, it's mainly light levels that are responsible for fall foliage colors. Sunny autumn days are needed for the brightest color displays, since anthocyanins require light. Overcast days will lead to more yellows and browns.

Photograph made along Bear Lake Road in Rocky Mountain National Park in northern Colorado.

Image copyright 2014 Jon Burch Photography

Uploaded

October 8th, 2014

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