Why leaves fall: the causes of the phenomenon
Do you know why leaves fall? And in some plants this happens periodically, while in others it is associated with the end of the life cycle. From our article you will learn about the causes and significance of this natural phenomenon.
When and why fall leaves from trees?
Traditionally it is believed that this phenomenon occurs only in the fall. Is it so? In fact, leaf fall only in some cases is a plant response to climate change. This decrease in air temperature, drought, reducing the length of daylight hours.
Why fall leaves at another time of year? The causes of this phenomenon may be diseases caused by the action of chemicals, harmful insects, an insufficient amount of fertilizer in the soil.
Leaf fall occurs in all plants without exception. Even evergreen pines and spruce change needles. It only happens gradually over a prolonged period.
With the onset of the cold season, most trees shed their leaves. This phenomenon, first of all, is a protection against excessive loss of moisture. It penetrates the plant from the soil.In winter, the water freezes. Therefore, the process of its entry into the plant organism becomes impossible.
In such conditions, the process of evaporation of water from the surface of the leaves does not stop. Although its intensity is reduced. That is why the fall leaves fall, protecting the plants from drying out.
This time of year nature is especially bright. This is due to the fact that the leaves change their green outfit to a more colorful one. It may be yellow, red, magenta, orange. The change in color is due to the interconversion of the plastids. In these permanent cellular structures are dyes, which are called pigments. Plastids chloroplasts contain chlorophyll. This pigment gives the green color of the leaves and stems of young plants.
In the fall, chloroplasts turn into plastids of another type. They are called chromoplasts containing anthocyanins and carotenoids. These substances cause a bright autumn vestment of plants.
Surely you noticed that the color of the foliage depends on the species. So, the leaves of maple and poplar become yellow, dogwood - purple, oak - red-brown. In some plants, the plastid interconversion process is not pronounced.Therefore, their falling leaves hardly change the light.
In winter and summer ...
Why do the leaves of flowering plants turn yellow and fall, and this does not happen for representatives of the gymnosperms? In particular, we are talking about the class conifers. The fact is that they have a number of devices for preserving moisture.
First of all, it is the shape and size of the leaves, which are called needles. They have a small area, which reduces the intensity of transpiration. The mouth, through which gas exchange and evaporation of water take place, are deepened into the thickness of the leaf. In addition, the wax is sealed for the winter. This ensures the almost complete cessation of moisture loss.
During the favorable period, sufficient amount of carbohydrates and water is accumulated in the needles to survive the winter. And oils provide protection from low temperatures.
Why we do not notice how conifers change foliage? Because it happens gradually. In this case, the plant does not grow naked for several months. And young needles grow immediately.
Mechanism of the phenomenon
What is the signal for plants to start falling leaves? This is a reduction in daylight hours.Reduced air temperature and rainy weather only accompany the main reason.
The leaves change color, which causes the process of overlapping vessels. A cell layer forms at the base of the stem. It prevents the descending flow of water with sugars dissolved in it. The result is the formation of anthocyanin pigments, which change the color of the leaf blade. Over time, the base of the petiole in the place of attachment to the shoot dries out. Leaf fall begins.
Leaf fall value
There is another reason explaining why leaves fall. On the one hand, if this did not happen, the plants would simply have dried out. But there is water in the leaves too. If it freezes, it will inevitably cause the death of plants.
The second reason for dropping leaves is protection against mechanical damage in winter against the mass of adhering snow. The trunks of trees with a powerful crown would just break under its pressure.
Together with the leaves of the plant get rid of the mass of harmful substances that have accumulated in them during the growing season. Therefore, this phenomenon is observed in all plants without exception. Even in the tropical belt, where there is no autumn and winter, leaf fall is observed.It only happens throughout the year. Therefore, almost not noticeable.
So, in our article we figured out why the leaves fall. This process is a protective reaction of plants from excessive loss of moisture, mechanical damage from snow sticking and glaciation, as well as a mechanism for purification from harmful substances.