Colourful time

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks... more

by Sonali Gangane

Title

Colourful time

Artist

Sonali Gangane

Medium

Photograph

Description

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, one or many colors that range from red to yellow. The phenomenon is commonly called fall colors and autumn colors, while the expression fall foliage usually connotes the viewing of a tree or forest whose leaves have undergone the change. In some areas of Canada and the United States, "leaf peeping" tourism is a major contribution to economic activity. This tourist activity occurs between the beginning of color changes and the onset of leaf fall.Chlorophyll and the green color

A green leaf is green because of the presence of a pigment known as chlorophyll, which is inside an organelle called a chloroplast. When they are abundant in the leaf's cells, as they are during the growing season, the chlorophylls' green color dominates and masks out the colors of any other pigments that may be present in the leaf. Thus the leaves of summer are characteristically green.In this leaf, the veins are still green while the other tissue is turning red. This produces a fractal-like pattern.Chlorophyll has a vital function: that of capturing solar rays and utilizing the resulting energy in the manufacture of the plant's food—simple sugars which are produced from water and carbon dioxide. These sugars are the basis of the plant's nourishment—the sole source of the carbohydrates needed for growth and development. In their food-manufacturing process, the chlorophylls themselves break down and thus are being continually "used up". During the growing season, however, the plant replenishes the chlorophyll so that the supply remains high and the leaves stay green.In late summer, as daylight hours shorten and temperatures cool, the veins that carry fluids into and out of the leaf are gradually closed off as a layer of special cork cells forms at the base of each leaf. As this cork layer develops, water and mineral intake into the leaf is reduced, slowly at first, and then more rapidly. It is during this time that the chlorophyll begins to decrease.Often the veins will still be green after the tissues between them have almost completely changed color.
Carotenoids





Cross section of a leaf showing color changes; click to enlarge.
Carotenoids are present in leaves the whole year round, but their orange-yellow colors are usually masked by green chlorophyll.[1] As autumn approaches, certain influences both inside and outside the plant cause the chlorophylls to be replaced at a slower rate than they are being used up. During this period, with the total supply of chlorophylls gradually dwindling, the "masking" effect slowly fades away. Then other pigments that have been present (along with the chlorophylls) in the cells all during the leaf's life begin to show through.[1] These are carotenoids and they provide colorations of yellow, brown, orange, and the many hues in between.
The carotenoids occur, along with the chlorophyll pigments, in tiny structures called plastids within the cells of leaves. Sometimes they are in such abundance in the leaf that they give a plant a yellow-green color, even during the summer. Usually, however, they become prominent for the first time in autumn, when the leaves begin to lose their chlorophyll.Carotenoids are common in many living things, giving characteristic color to carrots, corn, canaries, and daffodils, as well as egg yolks, rutabagas, buttercups, and bananas.Their brilliant yellows and oranges tint the leaves of such hardwood species as hickories, ash, maple, yellow poplar, aspen, birch, black cherry, sycamore, cottonwood, sassafras, and alder. Carotenoids are the dominant pigment in coloration of about 15-30% of tree species.
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Uploaded

February 24th, 2013