There is no more ordinary or inevitable occurrence than autumn leaves falling. However, have you asked yourself why this happens? And why?
During spring and summer, plants feel nice; they have enough light and food. Leaves are full of chlorophyll which absorbs sunlight and assists in the transformation of carbon dioxide and water into food.
Chlorophyll is bright green and it is plentiful, so other pigments from leaves cannot shine through. Therefore, leaves are green in most plants.
At the end of summer, days are growing shorter and there is less sun. In such conditions, a plant produces less and less chlorophyll. It withdraws from the leaves, causing other colours, such as purple, orange, brown and yellow to become more prominent, and at the same time, the production of these pigments increases.
For example, anthocyanin pigments give reddish and purplish colours, and carotenoids make orange and yellow colours, they, for example, give the colour to carrots, bananas and corn.
The colour of leaves, i.e. chemical reactions taking place inside them, is affected by temperature and the amount of water reaching the plant. For instance, the temperature above zero boosts the production of red, anthocyanin pigments, so the leaves mostly turn reddish. However, if, in early autumn, the temperature drops below zero, the red colour becomes less prominent.
If it rains a lot, the intensity of autumn colours is stronger. Scientists have concluded that the most spectacular autumn colours appear during warm summer days followed by cold nights without frost.
Besides the chlorophyll reduction in leaves, there is another thing going on in autumn: at the place where the leaf stalk connects with the branch, new layers of cells develop, and the leaf gradually separates itself from the tree. This simultaneously slows down and cuts the circulation of nutrients through the leaf.
When the time comes, even a gentle breeze is sufficient to completely tear the leaf and carries it away, and where its stalk has been, a miniature scar remains. This is how plants protect themselves from frost. Fallen leaves continue their second life by decomposing and feeding the soil, whence a plant absorbs the food.
M.Đ.
Illustration: Depositphotos/Markovka