Fall of the leaves ... Everyone knows what this phenomenon happens every autumn. But why do trees lose their lush outfit? The answer to this question can be found in our article.
What is leaf fall?
There is even a fairy tale about leaf fall.It tells that before all the plants were evergreen. Once the cold came, and all the animals went to warmer lands. And only a little bird with a wounded wing could not do it. With a request for help, she turned to the trees. But they were too busy. Only spruce and pine did not refuse her, hiding from the cold in their branches. And the juniper treated with berries. In punishment, Frost ordered the wind to tear the foliage from the indifferent trees for the winter.
The phenomenon we are considering is alwaysis a sign of approaching cold. This applies only to plants that grow in temperate zones with a clear change of seasons. However, the tropical representatives of this kingdom also shed their leaves. This usually happens before a drought.
What is leaf fall?This is a cyclical phenomenon in plant life. It can be associated with various adverse conditions, except for cold and drought. For example, this may indicate mechanical damage, defeat by viral infection or atmospheric toxins. Thus, dropping foliage is a plant defense reaction.
Causes fall foliage
So why do plants have to periodicallychange your green dress and what metamorphosis accompany this process? Before the leaves begin to fall, the leaves always change their color. This is due to the transformation of the plastids. Chloroplasts contain a pigment called chlorophyll, which makes the leaves green. It is in them that the process of photosynthesis takes place, one of the conditions of which is the presence of water.
When adverse conditions occur inBased on the sheet, a plug is formed. It prevents water from entering the leaf. Photosynthesis becomes impossible, so that chlorophyll is destroyed. But other pigments begin to appear, and the leaves become red, yellow, orange or purple color. Trees and shrubs seem to change their outfit.
Cork fabric, located at the base of the leaf blade, makes this place fragile. Even a small wind can cause the stalk to break away from the stem.
Deciduous plants
What is leaf fall in terms of physiology?This is the necessary protection against excessive loss of moisture. Since the surface of the leaf blade is the basis of transpiration, the plant simply disposes of it. Water is very necessary for the plant to experience the cold period, so losing it does not make sense.
Практически все покрытосеменные являются deciduous. But there are exceptions. For example, shrubs, lingonberry, wild rosemary, heather retain leaves. To do this, they have other devices to protect against water loss. So, on the underside of the leaves of the lingonberry are small dimples, the walls of which contain a mucous substance that absorbs water. The process of evaporation of water in wild rosemary prevent essential oils. They fill in special moves in the leaves of this plant.
Eternal greens
But there are plants that do not even know thatis leaf fall. These include almost all representatives of the Gymnosmies. "In the winter and in the summer - in one color" - this riddle familiar to all since the childhood about them. Leaves of gymnosperms are called needles. They are very narrow, so the evaporation of water from their surface is negligible.
Evergreen trees lose their foliage onlyas it gets older. On average, this occurs after 4-5 years. And in the spinous pine, needles can function for more than 40 years. The only gymnosperm that changes its cover when the season changes is the larch.
So leaf fall is a biological processwhich has an important protective significance in plant life. It may be associated with a change of season, damage to their organs or the onset of an unfavorable period.
