I love taking autumn pictures, I look forward to seeing them vast array of tree species and spectacular autumnal colors’. As a qualified Arboriculturist, I have studied exactly why leaves are green and what these colors’ in the leaves are.
During the spring and summer the leaves have served as little factories where the foods necessary for the tree’s growth are manufactured. This food-making process involves numerous cells containing chlorophyll, which gives the leaf its green color. This chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch.
The mixture of reds, purples, oranges and yellows is simply the result of chemical processes that take place in the leaves as the season changes from summer to winter.
The yellow of the leaves is caused by something called Xanthophyll; which are yellow pigments in the Carotenoid group. These have an important function of protecting leaves from absorbing too much light.
Carotenoids absorb blue wavelengths of the light spectrum, allowing longer wavelengths to be scattered and produce yellow color. In autumn foliage, the loss of chlorophyll (the green) reveals the carotenoids, which are left over in the chloroplasts. Carotenoids must pass their energy to the chlorophyll, because they cannot directly transfer sunlight energy.
Carotenoids can be red, orange or yellow. They function to help fuel photosynthesis by absorbing wavelengths of light not readily absorbed by chlorophyll. The reds you see on other trees are as a result of Anthocyanins. These pigments, in leaves, help to protect the leaf against excessive sunlight that can often damage some of the leaf tissues. Within these photosynthetic leaves, anthocyanins act as a sunscreen, and protect the cells from high-light damage by absorbing the blue-green and ultraviolet light, and protecting against photoinhbition.
Hopefully next time you see the autumn colors of the leaves you will appreciate there is much more than meets the eye…aren’t trees clever.
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