Leaf fall ... What such a phenomenon occurs every fall, everyone knows. But why do trees lose their lush outfit? You will find the answer to this question in our article.
What is leaf fall?
There is even a fairy tale about leaf fall. It tells us that before all the plants were evergreen. Once the cold came, and all the animals went to warmer climes. And only a small bird with a wounded wing could not do this. She turned to the trees for help. But they were too busy. Only the spruce and pine did not refuse her, sheltered from the cold in their branches. And the juniper was treated with berries. In punishment, Frost ordered the wind to tear foliage from indifferent trees for the winter.
The phenomenon that we are considering is always a sign of approaching cold weather. This applies only to plants that grow in the temperate zone with a clear change of seasons. However, tropical representatives of this kingdom also discard foliage. 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, a viral infection, or atmospheric toxins. Thus, dropping leaves is a protective reaction of the plant.
Reasons for leaf fall
So why do plants have to periodically change their green attire and what metamorphoses accompany this process? Before leaf fall begins, the leaves always change their color. This is due to the transformation of 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, a cork is formed at the base of the sheet. It prevents water from entering the leaf. Photosynthesis becomes impossible, as a result of which chlorophyll is destroyed. But other pigments begin to appear, and the leaves become red, yellow, orange or crimson. Trees and shrubs seem to change their outfit.
The cork cloth located at the base of the leaf blade makes this place fragile. Even a small wind can cause the stalk to come off the stem.
Deciduous plants
And what is leaf fall from a physiological point of view? This is a necessary protection against excessive moisture loss. Since the surface of the leaf blade is the basis of transpiration, the plant simply gets rid of it. Water is very necessary for the plant to survive the cold period, so losing it does not make sense.
Almost all angiosperms are deciduous. But there are exceptions. For example, shrubs of lingonberry, ledum, heather retain leaves. To do this, they have other devices to protect against water loss. So, on the underside of lingonberry leaves there are small dimples, the walls of which contain a mucous substance that absorbs water. Essential oils prevent the process of evaporation of water from Ledum. They fill special passages in the leaves of this plant.
Eternal green
But there are plants that do not even know what leaf fall is. These include almost all representatives of the gymnosperms department. “Winter and summer - one color” - this riddle familiar to everyone since childhood is precisely 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 only as it ages. On average, this happens 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 larch.
So, leaf fall is a biological process that has an important protective value in plant life. It may be associated with a change of season, damage to their organs or the onset of an unfavorable period.