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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 in the United States, and in much of Canada "leaf peeping" tourism between the beginning of color changes and the onset of leaf fall, or scheduled in hope of coinciding with that period, is a major contribution to economic activity.

Maple leaves
Contents
1 Chlorophyll and the green color
2 Pigments that contribute to other colors
2.1 Carotenoids
2.2 Anthocyanins
2.3 Cell walls
3 Function of autumn colors
3.1 Photoprotection
3.2 Coevolution
3.3 Allelopathy
4 Tourism
5 Climate influences
6 References
7 Further reading
8 External links
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Chlorophyll and the green color
A green leaf is green because of the presence of a pigment known as chlorophyll. 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.
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, 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.
Pigments that contribute to other colors
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 chlorophyll. 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. 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.
Anthocyanins
The reds, the purples, and their blended combinations that decorate autumn foliage come from another group of pigments in the cells called anthocyanins. Unlike the carotenoids, these pigments are not present in the leaf throughout the growing season, but are actively produced towards the end of summer. They develop in late summer in the sap of the cells of the leaf, and this development is the result of complex interactions of many influences - both inside and outside the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced.[citation needed]
During the summer growing season, phosphate is at a high level. It has a vital role in the breakdown of the sugars manufactured by chlorophyll. But in the fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant. When this happens, the sugar-breakdown process changes, leading to the production of anthocyanin pigments. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting color display. When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop.
Anthocyanins temporarily color the edges of some of the very young leaves as they unfold from the buds in early spring. They also give the familiar color to such common fruits as cranberries, red apples, blueberries, cherries, strawberries, and plums.
Anthocyanins are present in about 10% of tree species in temperate regions, although in certain areas - most famously Maine, New England - up to 70% of tree species may produce the pigment. In autumn forests they appear vivid in the maples, oaks, sourwood, sweetgums, dogwoods, tupelos, cherry trees and persimmons. These same pigments often combine with the carotenoids' colors to create the deeper orange, fiery reds, and bronzes typical of many hardwood species.

A display of vivid autumn leaves in eastern Vermont.
Cell walls
The brown color of leaves is not the result of a pigment, but rather cell walls, which may be evident when no coloring pigment is visible.
Function of autumn colors
Deciduous plants were traditionally believed to shed their leaves in autumn primarily because the high costs involved in their maintenance would outweigh the benefits from photosynthesis during the winter period of low light availability and cold temperatures. In many cases this turned out to be over-simplistic - other factors involved include insect predation, water loss, and damage from high winds or snowfall.
Anthocyanins, responsible for red-purple coloration, are actively produced in autumn, but not involved in leaf-drop. What use is the production of pigments in leaves that are about to fall? A number of hypotheses have been proposed, which fall into two cageories: interaction with animals, and protection from non-biological factors.
Photoprotection

Some trees, such as this American sweetgum at Keokea, Maui, develop bold fall colors in subtropical areas.
According to the photoprotection theory, anthocyanins protects the leaf against the harmful effects of light at low temperatures. It is true that the leaves are about to fall and therefore it is not of extreme importance for the tree to protect them. Photo-oxidation and photo-inhibition, however, especially at low temperatures, make the process of reabsorbing nutrients less efficient. By shielding the leaf with anthocyanins, according to the photoprotection theory, the tree manages to reabsorb nutrients (especially nitrogen) more... To get More information , you can visit some products about led replacement bulb, krypton bulb, table led light, g9 halogen bulbs, . The pendent light,victorian pendent lamp products should be show more here!