Brief reasons for leaf fall in autumn. Why do the leaves come off? What about in warm countries?
Everyone has seen how, with the onset of autumn, our broad-leaved trees dress in a multi-colored, beautiful outfit - yellow, purple, crimson-red. But this doesn't last long. Soon the lush robe begins to fade, the leaves fall off.
What is the reason for this phenomenon?
The reason is clear: preparation for life in winter conditions. The shedding of leaves by tree species in the fall is a biological adaptation to protect against water loss through evaporation when roots cannot absorb it from frost-bound soil. If there were leaves, the trees would die from drought, since moisture evaporates in the cold, and the supply stops. Leaf fall developed during the long evolution of plants and entered into the rhythm of life. Following this rhythm, plants prepare for winter in advance. As autumn approaches, the temperature drops and life processes weaken ( photosynthesis, transpiration), the destruction of pigments begins in the leaf. The green pigment is destroyed first - chlorophyll, other pigments – carotene, xanthophyll, anthocyanins, which are more persistent and last longer. The leaves become golden yellow, purple or purplish red, "Golden autumn". At the same time and even earlier, at the base of the petiole supporting the leaf, parenchyma cells begin to rapidly divide. As they round, they form large intercellular spaces, so that the tissue in this place becomes loose and fragile. A separating layer appears, the sheet breaks off and falls under the weight of its own plate. The wound is closed with a cork, forming a leaf scar with cut leaf marks. Leaf fall begins, which not only saves the tree from winter drought, but is also useful in other respects.
Among the chestnuts and bananas you can find the leaves of poplars, scorpions and robin. These five species are among the most punished by thirst and the heat that is dragging on these days. The botanical expert is not surprised that trees are devoid of leaves at the height of summer. This is a common thing due to the usual drought throughout the summer. What's happening is there may be more leaves on the ground this year because it's rained recently and it's been very windy, Sanchez says. Therefore, specimens planted there are most susceptible to high temperatures and lack of humidity.
If the crown of the tree had remained leafy for the winter, its branches would have broken off under the weight of the snow. With the fall of leaves, unnecessary waste is removed in the form of calcium oxalate. But valuable nutrients and building materials (starch, sugar, protein, fats, necessary salts) are moved to the stem in advance. Therefore, winter and autumn wood is richer in starch. Thanks to fallen leaves, trees seem to create organic and mineral fertilizers for themselves.
The explanation is simple, says the botanist: “The plants are new, they have no branches, air flows freely, this requires moisture and sweat from the plants.” In contrast, the trees in the Retiro Park or the Botanical Garden are more fortunate. They are covered with dense wood pulp, which creates a microclimate and retains moisture.
What determines the color of foliage in autumn?
The situation inside the grove is also decisive for the life of the leaves. "Those outside the block fall more than the interior, being more protected and having more shades," the technician points out Botanical Garden. He also recommends not trimming tree crowns as a precaution. And wait until the tree has grown before removing a branch. This means that it begins to give shade and thus create a humid microclimate in the ground.
The leaf carpet protects the roots from freezing. The phenomenon of leaf fall is a hereditarily fixed feature of broad-leaved woody plants. Even if these plants are grown in greenhouses, they will still shed their leaves at certain times of the year. Trees in hot countries shed their leaves before the onset of the dry season.
However, the cut must be done with care. “Pruning more than 20 centimeters condemns the tree in the middle of its life.” We are already in autumn, the days are shorter and colder. Some deciduous trees leave behind green while their cups turn red, yellow and orange.
Why does leaf fall happen?
Soon, many of the peninsula's deciduous forests will look like sunset, and soon, as winter sets in, the leaves will fall and the chests will be bare. The leaves of deciduous trees fall off in winter because they are no longer useful. Leaves are food plants for the rest of the plant. They use energy from the sun to convert carbon dioxide, water and other nutrients in the soil into other molecules that they need to grow and perform their vital functions. This is a process called photosynthesis.
Except deciduous plants, there is still large group evergreen, in which the leaves do not fall off all at once, but are gradually replaced by young ones instead of dying old ones.
The tropics and subtropics are rich in evergreens, where they are represented a huge amount species and form lush vegetation.
And in our latitudes, evergreen plants occupy vast spaces - from the temperate climate zone to the tundra, although they are represented by a more modest number of species: conifers (except larch), heather, wild rosemary, lingonberry.
Leaves, troubles in winter
This mechanism works very well when environmental conditions are mild. But when it's cold, the leaves are unpleasant. They cannot perform their function, so the plant gets rid of them. For example, when frozen, leaves fall off because the water they contain freezes, forming crystals that damage their tissue. On the other hand, with frozen soil, the roots cannot absorb water or nutrients since they can only be taken in if they are dissolved.
As a consequence, the plant dies of thirst when it loses water from its leaves and is not replaced by its roots. “Leaf colors are caused by plant chemicals.” To avoid this death when the cold sets in, the plant cuts the sap supply to the leaves, removes chlorophyll and other beneficial substances from the leaves and stores them in other tissues for use in the spring.
Evergreen plants do not have permanent leaves. Needles pine trees lives from 3 to 5 years, fir– from 3 to 10 years, yew– from 6 to 10 years. The leaves of deciduous plants live only for a few months - from spring to autumn.
LEAF FALL LEAF FALL
leaf fall usually occurs in trees and shrubs, less often in herbs (nettle, impatience). Leaves can fall all at once during a certain period of the year (for example, in deciduous trees) or gradually one at a time over a long period of time (in evergreen plants). Deciduous trees in the humid tropics. forests stand without leaves, sometimes only a few. days, in the temperate zone - up to 8-9 months. L. - normal physiol. process associated with leaf aging. Before L., deep biochemical and physiological processes occur in the leaves. and structural changes. Chlorophyll is usually destroyed, carotenoids persist longer and determine the autumn color of leaves. Nutrition substances from the leaves flow into storage organs (tubers, rhizomes, etc.) to growth points, to growing young leaves. L.'s mechanism is associated with the appearance at the base of the leaf (or main petiole) of a separating layer of easily separated parenchyma cells. The conductive bundles that hold the leaf on the stem are torn under the weight of the leaf and gusts of wind. L. is an adaptation developed in the process of evolution to reduce the surface of ground organs in unfavorable conditions, which reduces moisture loss and prevents breakage of branches under the weight of snow.
Chlorophyll is a chemical compound that is important for harnessing solar energy and the pigment that gives leaves their characteristic green color. When a leaf loses chlorophyll, the color of other substances that were masked appears. Each plant has its own characteristics, so some chemical compounds predominate over others. For example, red and blue tones are produced by the accumulation of anthocyanin, yellow tones are a product of carotenoids and brown tannins.
Hormones are organic molecules that, even in small quantities, can influence the physiology of plants and animals. Hormones play an important role in the growth, flowering and maturation of cannabis. In this article, we explain how plant hormones work in plants and how they help them bloom.
.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief M. S. Gilyarov; Editorial Board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected - M.: Sov. Encyclopedia, 1986.)
leaf fallLeaf fall caused by seasonal climate conditions (winter cold, summer drought), the internal rhythm of plant development (organic dormancy), plant damage by pests and diseases, or unfavorable soil conditions. In this case, the color of the leaves often changes (the amount of red pigments increases, chlorophyll is destroyed), and an outflow of nutrients occurs to other organs. A separating layer of cells appears at the base of the petiole, facilitating the separation of the leaf. Leaf fall also occurs in evergreen plants, but their leaves fall off gradually, simultaneously being replaced by new ones.
Why do leaves fall in autumn?
Hormones are produced in any part of the plant and are transported throughout. Expressed in a simplified way, we could say that these are signals that can be emitted or received by any part of the installation. A leaf, for example, can send a signal to the tip of a stem to make flowers grow. The most well-known phytohormones are auxin, gibberellin, cytokinin, ethylene and abscisic acid. In addition, hormone-like effects have been attributed to brasinosteroids, salicylates, and jasmonates.
The specific object of his research was the effect of light on the direction of growth in oats. The phytohormone whose effect was tested in these experiments was auxin. Auxin is produced in the apical meristems of the plant and affects, among other things, water absorption, cell division and cell elongation. Because of their effect, various forms of auxins are commonly used in preparations that stimulate root growth.
.(Source: “Biology. Modern illustrated encyclopedia.” Chief editor A. P. Gorkin; M.: Rosman, 2006.)
Synonyms:
See what "LEAF FALL" is in other dictionaries:
Leaf fall... Spelling dictionary-reference book