Every autumn, the leaves change their color, they turn yellow, redden or turn purple and gradually fall, they become dry and brittle. The rustling arises precisely because of these properties. Why do leaves turn yellow in autumn? Some believe that this comes from frost. As if this cold had killed the summer beauty, and now the leaves are falling to the ground, gradually covering it with a bright rustling carpet. However, this is not at all true. If you are careful, you will immediately notice that the leaves begin to turn yellow and fall off much earlier than the first frosts. Leaf fall is only a seasonal phenomenon, and its causes are hidden in the trees themselves, in their biological mechanism of the struggle for survival in harsh seasonal conditions.
A small child asks his parents why the leaves turn yellow in the fall? It is very important to answer this question correctly. Indeed, based on what children are told in their small years, their further worldview is taking shape. If the leaves do not fall on time, then the plants may suffer or die not from freezing, but from the lack of moisture. Cold air can dry no less than hot. The liquid in the soil freezes, and the suction capacity of the roots stops, and soon freezes completely. When the flow of moisture to the leaves stops, the
evaporation of water through their surface still continues. That is why the leaves turn yellow in the fall. They protect their tree from death. If they remained on the tree, then all the moisture would immediately evaporate from the branches through their surface. Thanks to this protective mechanism, plants are freed from a large excess area. And in order for the tree to dump them, first you need to turn the leaves into dead leaves, which then fall off.
When the leaves turn yellow in the fall, all processes in the plant stop, life itself freezes. This is one of the irreversible natural phenomena. When light changes on the street, the biological clock alarm goes off at the leaves, and they begin to change color. This process can be divided into three stages:
- yellowing of some leaves;
- coloring the lit sides of crowns,
- completion of the process and the first fall.
It is impossible not to notice that all the trees do this at different times, and the forest becomes bright uneven. When do leaves start to turn yellow? In the fall. On the lightened side of the tree, the process is faster, and on the shaded leaves they remain green for a long time.
From the point of view of the biochemical process, this is due to the fact that they cease to produce chlorophyll. In the summer, yellow pigment is also present in the leaves, but its amount is insignificant compared to green. Now it is becoming more and more noticeable. And another interesting feature: red foliage comes across only in a well-lit and fairly cool place. Anthocyanins together with carotenoids are responsible for the saturated color.
All this explains why the leaves turn yellow in the fall. However, this does not happen with all trees. Leaves of rosemary, cranberries, juniper, heather and lingonberries do not turn yellow, under the snow they remain green, because they evaporate very little moisture.