Why do tree leaves turn colors in the fall?

Answer 1

Inside the leaf there are millions of tiny discs filled with a green pigment called chlorophyll. These green 'packages' are used to trap sunlight which is used as an energy source to produce glucose (a type of sugar) in a process called photosynthesis.

There are other packages that are coloured in yellow (xanthrophyll) and some in orange (carotene), which are used in other processes in the leaf.

During the summer (in the presence of sunlight and plenty of water photosynthesis can take place) and the green packages are very active, so they hide away (or mask) the yellow and orange ones.

As fall approaches the weather grows colder and the hours of sunshine shrink as well. The trees 'realise' that winter is approaching and so they begin to prepare for it. Layers of cells grow over the tubes that carry water and glucose closing them up and making photosynthesis impossible (which requires water and sunlight).

The green chlorophyll starts to break down and disappear, and so the colours of the other 'packages' can be seen, the yellow xanthrophyll and the orange carotene. As the tubes that carry glucose are trapped as well, sugar remains in the leaves, which with time (due to sunshine and cold) give the leaves a red or purple colour. As the leaves no longer have water and glucose flowing around, they slowly die, turning into brown (chlorophyll dies first, then xanthrophyll and carotene).

A:

Deciduous plants are 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.[1] However, there is no reason why leaf fall should necessarily be preceded by the production of vivid autumn colors, and the function of the color change is still uncertain. Autumn colors (especially red) are not just due to the breakdown of chlorophyll; in fact anthocyanins (red-purple) are actively produced in autumn. What use is the production of pigments in leaves that are about to fall? A number of hypotheses have been proposed, including photoprotection, coevolution and allelopathy:

Photoprotection

According to the photoprotection theory, anthocyanins protects the leaf against the harmful effects of light at low temperatures[2][3]. 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 efficiently.

Coevolution

According to the coevolution theory [4], 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 will have an advantage because they reduce their parasite load. The coevolution theory of autumn colors was born as a branch of evolutionary signalling theory. It is a general feature of biological signals that, when a signal is costly to produce, it is usually honest - that is it reveals the true quality of the signaller, because it does not pay for a low quality individual to cheat. Autumn colors might be a signal if they are costly to produce, or they could be an index, which is maintained because it is impossible to fake (because the autumn pigments are produced by the same biochemical pathway that produces the chemical defenses against the insects). Although it is not certain that aphids have red receptors, there is some evidence that they preferentially avoid trees with red leaves. This is what the coevolution theory predicts at the intraspecific level (more insects on dull leaves). It is also known that tree species with bright leaves have more specialist aphid pests than do trees lacking bright leaves[5], which is the interspecific prediction of the theory (autumn colors are useful only in those species coevolving with insect pests in autumn). The coevolution hypothesis has been subjected to criticism.[6]

The change of leaf colors prior to fall have also been suggested as adaptations that may help to undermine the camouflage of herbivores.[7]

Many plants with berries attract birds with especially visible berry and/or leaf color, particularly bright red. 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).

Allelopathy

Researchers at New York's Colgate University have found evidence that the brilliant red colors of maple leaves is created by a separate processes then those in chlorophyll breakdown. At the very time 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 in what is known as allelopathy. (Frey & Eldridge, 2005)

Answer 2

The trees shut down their ability to make food as the days grow shorter. As chlorophyll dissipates from the leaves, the green color goes along with it leaving behind the colors we see in fall.

Answer 3

Trees absorb their chlorophyll molecules during autumnal months to keep them from being lost as leaves fall from the tree. Unlike carotenoids, which are easily replaced with new leaf growth, chlorophyll takes a tremendous amount of energy to produce. By withdrawing it back into the trunk over the winter, the tree can save its energy for spring growth, when the chlorophyll will be sent back into the leaves so photosynthesis can occur.

Answer 4

The leaves of any plant are its little food storage vessels, when it gets cold out the tree doesnt have any other source of food besides the leaves, so it sucks all the food out of the leaves and they dry up and change colors, eventually falling off the tree.

Answer 5

Because winter is dry and the plants stop making food and also the chlorophyll gose away

Answer 6

It is amazing to watch nature change seasons, so many different colors appear in each season. Leaves change colors in fall because many of the leaves are dying.

Answer 7

They stop producing chlorophyll, which reflects green wave light.

Answer 8

that's how god made the trees

Answer 9

Due to senescense