Why do trees shed their leaves in autumn?

Leaf fall began in the natural territories of Moscow

Trees and shrubs began to escape the drought and shed their leaves as early as August. The fact is that the leaf not only breathes, but also evaporates the moisture that the plant absorbs by the roots from the soil. To reduce moisture loss, green spaces get rid of some of the leaves. Therefore, this year, yellowed leaves and a slight leaf fall could be observed ahead of time.

The main leaf fall in the natural conditions of Moscow falls on the end of September – the beginning of October and lasts until the end of the first decade of October. After the first 2-3 frosts, the foliage will fall off completely. A severe frost can cause half of the foliage to be on the ground the very next day, and within some 5-7 days the trees will lose the remaining leaves.

Why do leaves turn different colors – yellow, orange, burgundy? The leaves of plants contain various pigments, the main ones are chlorophyll and carotenoids. The green pigment – chlorophyll – forms the summer color of the foliage familiar to us. Carotenoids (carotenes and xanthophylls) give yellow and orange hues. The process of photosynthesis, familiar to every biology lesson, is impossible without pigments. They work as “catchers” of solar energy. Chlorophyll and then carotenoids collect photons of light to provide energy for the basic reactions of photosynthesis.

Autumn is a difficult time for plants. The change of seasons is stressful for them: the day is shortening, the temperature drops, and soon the amount of water will decrease significantly. Trees and shrubs are actively preparing for winter, shedding leaves. First, chlorophyll is destroyed along with proteins and nucleic acids. Some of the substances from the falling leaves will go into the wood. Xanthophylls (shades of yellow) and carotenes (shades of orange) last longer, although they will also be destroyed as a result. And there are also stress pigments – anthocyanins, which are synthesized in autumn and give the plants a reddish tone.

Chlorophyll in plants is destroyed at an unequal rate. The content of pigments varies not only in different plant species, but may also differ in individual parts of the crown of one tree. Together, the pigments create a picturesque picture. Therefore, the natural areas of the capital are so colorful in autumn.

Nina DONSKIKH.

Photo of the author.

Based on materials “My House Moscow”.