All love an autumn leaf fall when "birches yellow rezboyblestit in an azure blue". But what is a leaf fall from the biological point of view and what its value in life of plants?
Leaf fall from the biological point of view
In places where frosts or droughts come annually, it is possible to see a leaf fall: the majority of perennial plants - bushes and trees - dump the leaves before approach of these adverse weather conditions. The leaf fall is a natural separation of leaves from a stalk (axial part of escape) which occurs, as a rule, once in a year.
Some plants dump leaves every year: in hot and droughty areas it is, for example, a baobab and bombaksa, in the temperate climatic zone are the trees and bushes known to us, for example a birch, a linden, currant and so on. Plants with long-term leaves dump them not everything at once, and gradually as, for example, cowberry or coniferous trees. Plants which dump all foliage every year are called listopadny, and plants with long-term leaves are called evergreen.
Listopadny plants will annually dump foliage even if to transfer them to other climatic conditions, for example, there where there are no cold winters.
How does dying off of leaves happen?
With approach of time of a leaf fall the leaves grow old. In process of their aging the intensity of breath decreases, chlorolayers degrade, from a leaf in a stalk flow plastic substances (amino acids, carbohydrates), some salts collect (for example, calcium oxolat). About the basis of a leaf the separating layer which consists of easily stratified matter - a parenchyma is formed. On a parenchyma the leaves separate from a stalk. The leaf fall begins.
Why the leaf fall is necessary?
In winter time the plants lack water. In the earth, water is in the frozen state – in a condition of ice, and it cannot get into roots of trees and bushes. At the same time from a surface of leaves the process of evaporation goes continuously. In this case, value of a leaf fall - protection of plants against drying.
Evergreen plants adapt to the shortage of water in a different way – the surface of their leaf is so small (for example, coniferous breeds) that they evaporate not enough moisture.
One more reason of dropping leaves - protection against mechanical damages which can result from sticking of snow to a leaf. Besides, the leaf fall serves as the mechanism of clarification of an organism of a plant from hazardous substances. By fall in leaves the huge amount of salts and hazardous mineral substances collects. For this reason the fallen-down foliage cannot be burned – it is very toxic. Thus, the leaf fall is a necessary phenomenon in life of plants. It represents natural protection of plants against adverse weather conditions.