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The autumn and the fall of leaves

Typical fall foliage in red maple country, the Adirondacks of New York English country lane in the autumn 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.

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Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced. 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.

  1. Others, like many oaks, display mostly browns. At the point where leaf stem meets twig or branch is an array of cells called the abscission layer.
  2. As the days get shorter, the reduced amount of light signals that a change in season is well and truly on the way.
  3. This article has been reviewed by the following expert. Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot.

They also give the familiar color to such common fruits as cranberriesred applesblueberriescherriesstrawberriesand plums. These same pigments often combine with the carotenoids' colors to create the deeper orange, fiery reds, and bronzes typical of many hardwood species.

Cell walls[ edit ] 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. Anthocyanins, responsible for red-purple coloration, are actively produced in autumn, but not involved in leaf-drop. A number of hypotheses on the role of pigment production in leaf-drop have been proposed, and generally fall into two categories: According to the photoprotection theory, anthocyanins protects the leaf against the harmful effects of light at low temperatures.

Autumn leaves

Photo-oxidation and photoinhibition, 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 efficiently.

Coevolution[ edit ] According to the coevolution theory, [15] the colors are warning signals towards insects that use the trees as a host for the winter, for example aphids. If the colors are linked to the amount of chemical defenses against insects, then the insects will avoid red leaves and increase their fitness; at the same time, trees with red leaves have an advantage because they reduce their parasite load.

This has been shown in the case of apple trees where some domesticated apple varieties, unlike wild oneslack red leaves in autumn. A greater proportion of aphids that avoid apple trees with red leaves manage to grow and develop compared to those that do not.

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Hamilton in 2001 as an example of evolutionary signalling theory. Autumn colors would be a signal if they are costly to produce, or be impossible to fake for example if autumn pigments were produced by the same biochemical pathway that produces the chemical defenses against the insects.

The birds get a meal, while the shrub, vine, or typically small tree gets undigested seeds carried off and deposited with the birds' manure. Poison ivy is particularly notable for having bright-red foliage drawing birds to its off-white seeds which are edible for birds, but not most mammals.

Why Do Leaves Change Color In Fall?

Allelopathy[ edit ] The brilliant red autumn color of some species of maple is created by processes separate from those in chlorophyll breakdown.

When the tree is struggling to cope with the energy demands of a changing and challenging season, maple trees are involved in an additional metabolic expenditure to create anthocyanins. These anthocyanins, which create the visual red hues, have been found to aid in interspecific competition by stunting the growth of nearby saplings allelopathy.

Leaf peeping Although some autumn coloration occurs wherever deciduous trees are found, the most brightly colored autumn foliage is found in four or five regions of the world: The main reason was the different effect of the ice ages—while in North America, species were protected in more southern regions along north—south ranging mountains, which was not the case in Europe.

Why trees shed their leaves

Also, other factors, such as increasing ozone levels close to the ground tropospheric ozone pollutioncan negate the beneficial effects of elevated carbon dioxide. Trip of a Lifetime - Telegraph".

Retrieved 18 June 2015.