Autumn leaf color

[6] Chlorophyll has a vital function: it captures solar rays and uses the resulting energy in the manufacture of the plant's food – simple sugars which are produced from water and carbon dioxide.

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.

The reds, the purples, and their blended combinations that decorate autumn foliage come from another group of pigments in the cells called anthocyanins.

It has a vital role in the breakdown of the sugars manufactured by chlorophyll, but in autumn, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant.

When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop.

They also give the familiar color to such common fruits as cranberries, red apples, blueberries, cherries, strawberries, and plums.

[6] 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.

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.

[11] In many cases, this turned out to be oversimplistic – other factors involved include insect predation,[12] water loss, and damage from high winds or snowfall.

A number of hypotheses on the role of pigment production in leaf-drop have been proposed, and generally fall into two categories: interaction with animals, and protection from nonbiological factors.

A greater proportion of aphids that avoid apple trees with red leaves manage to grow and develop compared to those that do not.

[citation needed] The change of leaf colors prior to fall have also been suggested as adaptations that may help to undermine the camouflage of herbivores.

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

These anthocyanins, which create the visual red hues, have been found to aid in interspecific competition by stunting the growth of nearby saplings (allelopathy).

The main reason is the different effect of the Ice ages – while in North America, species were protected in more southern regions along north–south ranging mountains, this was not the case in much of Europe.

[27] Experiments with poplar trees showed that they stayed greener longer with higher CO2 levels, independent of temperature changes.