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When winter is just around the corner, not only do many animals make supplies. The trees and bushes are now creating a nutrient cushion for the next season as well: the nitrogen-rich green leaf pigment (chlorophyll), with which plants use the energy of sunlight to produce sugar (photosynthesis), is now broken down into its components and stored. During this process, it becomes apparent that the leaves also contain orange and yellow dyes (carotenoids and xanthophylls). Although they are always present, they are overshadowed by chlorophyll in spring and summer. Both dyes are also involved in the photosynthesis process.
The ginkgo is known for its golden autumn color
From green to yellow
Trees like the ginkgo decompose the carotenoids in the fall simultaneously with the chlorophyll. With them, the leaf color changes seamlessly from green to yellow, because the yellow xanthophylls are not recycled, but remain in the leaf cells. For other trees such as the vinegar tree, it is very nice to see in autumn how the mining process takes place over the colors green, red and yellow in stages.
The leaves of the wild wine turn bright red to purple
Red as the sunset
Trees with red or reddish-violet autumn colors like the sweetgum tree are very popular with hobby gardeners. For these shades is another dye group responsible: the anthocyanins. Their function is not yet scientifically clarified, but at least one knows today that they do not play a role in the photosynthesis. The botanists suspect that the anthocyanins are formed only in the fall and act as a sunscreen. They are likely to protect the degradation products of the other dyes from uncontrolled decomposition by the UV light. Therefore, the red leaf color is particularly intense in cool, sunny autumn weather. Incidentally, in the case of red-leaved trees such as blood beech or blood plum, anthocyanins are also responsible for the color of the leaves.
The vinegar tree shows all autumn colors
In the end, the leaves fall
The leaves eventually fall to the ground because a thin layer of cork forms parallel to the degradation processes between leaf and branch. It seals the connecting channels and prevents parasites and pathogens from entering. As soon as the cork layer is finished, a small gust of wind is enough to detach the blade. However, some trees, such as beech trees, can not quite break with their old leaves. In some cases, they stick to the new shoot in spring.