Every autumn, the leaves change their color, they turn yellow, red or purple and gradually fall off, becoming dry and brittle. The rustling occurs precisely due to these properties. in the fall? Some believe this is due to frost. As if it was the cold that killed the summer beauty, and now the leaves fall to the ground, gradually covering it with a bright rustling carpet. However, this is not at all true. If you are careful, you will immediately notice that the leaves begin to turn yellow and fall off much more quickly. earlier than the first frosts. Leaf fall is only a seasonal phenomenon, and its causes are hidden in the trees themselves, in their biological mechanism of struggle for survival in harsh seasonal conditions.
A small child asks his parents why the leaves turn yellow in the fall? It is very important to answer this question correctly. After all, based on what children are told in their early years, their future worldview is formed. If the leaves do not fall on time, the plants may suffer or die not from freezing, but from lack of moisture. Cold air can dry no less than hot. The liquid in the soil freezes, and the suction ability of the roots stops, and soon stops altogether. When the flow of moisture to the leaves stops, it still continues through their surface. This is why the leaves turn yellow in the fall. They protect their tree from death. If they remained on the tree, then all the moisture would immediately evaporate from the branches through their surface. Thanks to this protective mechanism, plants are freed from large excess areas. And in order for a tree to shed them, it first needs to turn the leaves into dead leaves, which then fall off.
When the leaves turn yellow in the fall, all processes in the plant stop, life itself freezes. This is one of the irreversible phenomena of nature. When the light outside changes, the leaves' biological clock alarm goes off and they begin to change color. This process can be divided into three stages:
- yellowing of some leaves;
- coloring of the illuminated sides of the crowns,
- completion of the process and the first fall.
It's impossible that all trees do this in different times, and the forest becomes bright unevenly. When do the leaves start to turn yellow? In autumn. On the illuminated side of the tree the process occurs faster, and on the shaded side the leaves remain for a long time. green.
From the point of view biochemical process, this is due to the fact that they stop producing chlorophyll. IN summer time yellow pigment is also present in the leaves, but its amount is insignificant compared to green. Now it is becoming more and more noticeable. And one more interesting feature: red foliage is found only in a well-lit and fairly cool place. Anthocyanins together with carotenoids are responsible for the rich color.
All this explains why the leaves turn yellow in the fall. However, this does not happen with all trees. The leaves of wild rosemary, cranberry, juniper, heather and lingonberry do not turn yellow; under the snow they remain green, because they evaporate very little moisture.
Do you know why leaves fall? Moreover, in some plants this occurs periodically, while in others it is associated with the end life cycle. From our article you will learn about the causes and significance of this natural phenomenon.
When and why do leaves fall from trees?
It is traditionally believed that this phenomenon occurs only in autumn. Is this true? In fact, leaf fall is only in some cases a plant response to climate change. This is a decrease in air temperature, drought, a decrease in the duration daylight hours.
Why do the leaves fall at other times of the year? The causes of this phenomenon may be diseases caused by the action chemicals, harmful insects, insufficient quantity fertilizers in the soil.
Leaf fall occurs in all plants without exception. Even evergreen pines and spruces change their needles. It just happens gradually over a long period.
Golden autumn
With the onset of the cold season, most trees shed their leaves. This phenomenon, first of all, is a protection against excessive moisture loss. It penetrates into the plant from the soil. In winter the water freezes. Therefore, the process of its entry into the plant organism becomes impossible.
Under such conditions, the process of evaporation of water from the surface of the leaves does not stop. Although its intensity is decreasing. This is why the leaves fall off in the fall, protecting the plants from drying out.
At this time of year, nature is especially vibrant. This is due to the fact that the leaves change their green outfit to a more variegated one. It can be yellow, red, purple, orange. The color change is explained by the interconversion of plastids. These permanent cellular structures contain coloring substances called pigments. Chloroplast plastids contain chlorophyll. This pigment gives the green color to the leaves and stems of young plants.
In autumn, chloroplasts transform into a different type of plastid. They are called chromoplasts, containing anthocyanins and carotenoids. These substances determine the bright autumn clothing of plants.
Surely you have noticed that the color of the foliage depends on the species. Thus, maple and poplar leaves acquire yellow, dogwood - purple, oak - red-brown. In some plants, the process of interconversion of plastids is not clearly expressed. Therefore, their falling leaves practically do not change the light.
Winter and summer...
Why do the leaves of flowering plants turn yellow and fall off, but this does not happen in representatives of the gymnosperm division? In particular, we are talking about the coniferous class. The point is that they have a whole series devices for maintaining moisture.
First of all, this is the shape and size of the leaves, which are called needles. They have a small area, which reduces the rate of transpiration. The stomata, through which gas exchange and water evaporation occur, are deepened into the thickness of the leaf. In addition, they are sealed with wax for the winter. This ensures an almost complete cessation of moisture loss.
For favorable period The needles accumulate enough carbohydrates and water to survive the winter. And oils provide protection from low temperatures.
Why don't we notice how conifers change their leaves? Because this 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 begin leaf fall? This is a reduction in daylight hours. Lower air temperatures and rainy weather only accompany the main reason.
The leaves change color, which causes the process of blocking of blood vessels. A layer of cells forms at the base of the petiole. It prevents the downward flow of water with sugars dissolved in it. As a result, anthocyanin pigments are formed that change color leaf blade. Over time, the base of the petiole dries out at the point of attachment to the shoot. The leaves are starting to fall.
The meaning of leaf fall
There is another reason why leaves fall. On the one hand, if this did not happen, the plants would simply dry out. But leaves also contain water. If it freezes, it will inevitably lead to the death of the plants.
The second reason for shedding leaves is protection from mechanical damage in winter from the mass of adhered snow. Tree trunks with a powerful crown would simply break under its pressure.
Together with the leaves, the plants get rid of the mass harmful substances, which accumulated in them during the growing season. Therefore, this phenomenon is observed in all plants without exception. Even in the tropical zone, where there is no autumn and winter, leaf fall is observed. It just happens throughout the year. Therefore, it is practically invisible.
So, in our article we figured out why leaves fall. This process is a protective reaction of plants against excessive loss of moisture, mechanical damage from snow and icing, as well as a mechanism for purifying harmful substances.
Why do leaves turn yellow and fall off in autumn?
The summer season ends with the last fallen leaves from trees and bushes. For many people, bare plants cause despondency and longing for summer. But autumn is beautiful! No wonder so many poetic lines are dedicated to this time of year. Why do the leaves of some plants turn red while others turn yellow? And why do the leaves fall?
Leaf fall is the most striking sign of autumn. These plants adapt to unfavorable seasonal conditions. Seasonal variability of plants begins with northern latitudes and gradually moves south. Leaf fall repeats itself every year and always delights us with its bright colors- from yellow and orange to pink and purple. The leaves fly away even with evergreens in the subtropics and tropics. Only there they do not fall all at once, but gradually throughout the year, and therefore it is not so noticeable.
In autumn it gets colder, and water flows into plants from the roots to the leaves at a slower pace. But it's not main reason leaf fall. Offensive unfavorable conditions is a signal for the transition of plants to a new life cycle, which is embedded in the genetic code. This indicates to us that the autumn shedding of leaves is not a direct consequence of the unfavorable conditions that have occurred. It's together with in winter dormancy is included in the plant development cycle itself. There is also a way to make sure that leaf fall is a physiological process. Why does the leaf separate from the branch? It turns out that with the onset of cold weather, a cork layer forms at the base of the petiole, where the leaf is attached by a “leaf pad” to the branch. The cells of this layer have smooth walls and are easily separated from each other. As soon as the wind blows a little harder, the sheet separates from the cork layer.
The green color of leaves in summer is due to a large number chlorophyll pigment contained in them. This pigment “feeds” the plants, since it is with its help that the plant is exposed to light. carbon dioxide and water synthesizes organic substances and, first of all, the main sugar - glucose, and from it - all other nutrients. Chlorophyll contains iron, and when it breaks down, oxides are formed that have a brown-yellow color. The destruction of chlorophyll occurs more intensely in the light, that is, in sunny weather. That is why in cloudy, rainy autumn the leaves retain their green color longer. When it comes in autumn sunny days the leaves take on a golden-red color.
However, along with chlorophyll green leaves also contain other pigments - yellow xanthophyll and orange carotene (it determines the color of carrot roots). In summer, these pigments are invisible, as they are masked by a large amount of chlorophyll. In autumn, as vital activity in the leaf fades, chlorophyll is gradually destroyed. This is where the yellow and red shades of xanthophyll and carotene appear in the leaf.
In addition to gold, the autumn colors of trees contain crimson shades. This color comes from a pigment called anthocyanin. Unlike chlorophyll, anthocyanin is not associated inside the cell with plastic formations (grains), but is dissolved in cell sap. When the temperature decreases, as well as in bright light, the amount of anthocyanin in the cell sap increases. In addition, stopping or delaying synthesis nutrients in foliage they also stimulate the synthesis of anthocyanins.
Fallen leaves can retain their shape and color for a few more days, and then they begin to dry out and acquire a brown color that is not very pleasant to the eye. Some of the leaves remain in place under the trees and bushes, while some are carried away by the wind outside the site. For aesthetic reasons, a gardener is often tempted to clear the soil of fallen leaves. Is it necessary? After all, the leaves contain the same chemical compounds that were taken by plants from the soil. True, they acquired a slightly different chemical composition and entered plant-derived organic matter. Once on the soil surface, the leaves become “prey” for a great variety of different living organisms. Among them the most important role in the disposal of leaves belongs to earthworms. The products of their vital activity (the excrement of worms are called caprolites) contain the entire set of nutrients for plants in almost finished form. So the leaves, having entered the biological cycle of substances, returned to the soil what they once received in the plant.
Now decide for yourself - to remove leaves from under the trees or not? There are two ways to save beneficial properties fallen leaves. The first is to leave it in place until spring, followed by digging. At the same time, the leaves will insulate top layer soil. The second path will be somewhat more difficult and take longer. Collect leaves in compost pit and after a year or two return it under the trees in a rotted state.
V. A. Rassypnov , professor of ASAU
Sometimes autumn appears before us in gray color. Gloomy leaden sky gray wall rain - it’s easy to get discouraged. But there is also a bright spot to lift your spirits! The autumn color of trees always delights and pleases the eye.
Why are the leaves green?
The green color of the leaves is due to the pigment chlorophyll. It is this substance that provides plants with the synthesis of oxygen and other important substances from carbon dioxide and water in the light. Chlorophyll is actively produced in the warm season, when trees receive enough nutrients and moisture from the soil.
The trees release the oxygen obtained through synthesis into the atmosphere, and absorb the rest of the substances themselves. With the onset of autumn, the activity of trees decreases; they receive less and less nutrition from the soil. To continue the process of photosynthesis, the foliage continues to draw nutrients from the trunk. In turn, the tree, in order to preserve reserves of substances for the winter, begins to take magnesium from the leaves, which leads to the destruction of chlorophyll. Once the green pigment begins to break down, other shades appear. Why is one leaf red, another yellow, and the third variegated, like an artist’s palette? It turns out it's a matter of chemical composition.
What determines the color of leaves
- We can see the yellow color thanks to the xanthophyll pigment.
- Carotene is responsible for the orange color.
- The leaves become crimson and red under the influence of anthocyanin. It is dissolved in the cell sap of the leaf, and the amount of pigment increases with bright light and lower temperatures.
Pigments of all these colors are always present in plant cells, but during the period of active chlorophyll production, the green color covers all the others. But a leaf becomes brown or brown when it completely loses its coloring pigments. At this time, empty cell walls that are brown in color become visible to us.
When can leaves change color?
As a rule, the color of foliage changes in the fall, because it is at this time of year that the level of plant activity decreases. It's getting colder outside, and trees are getting less nutrients from the soil. Chlorophyll begins to break down.
At the same time, its destruction occurs most actively in the light. If the weather outside is cloudy and rainy, then oaks, maples, and birches will remain green longer. If there are clear sunny days outside, the trees will change their color much faster.
In hot and dry summers, when plants lack moisture and sunlight in excess, the leaves may also lose their chlorophyll and green color.
What happens to coniferous trees in autumn?
Representatives of conifers retain their green color with the onset of the cold season: spruce, pine, fir, juniper. This is because their foliage area is small and they require few nutrients to sustain life.
But even conifers lose needles, but this happens gradually. The needles are not replaced simultaneously, but in parts. 
Catch and save bright moments of autumn
Colored foliage does not last long in forests and parks, plant activity decreases and gradually fades away, they “fall asleep.” A special cork layer appears between the leaf and the trunk, and the leaf is separated from the branch. Very little time will pass, and the trees will already be completely bare.
The bright colors and beauty of autumn are fleeting. Have time to enjoy these moments and capture them in your memory. A pleasant autumn pastime is a walk through a colorful forest or park, with soft leaves rustling under your feet. rich shades. Only at this time of year can you find a special silence in the forest, when the rustling of leaves can be clearly heard. 
An unforgettable sensation will be given by a running jump into a soft pile of colorful freshly fallen leaves, the main thing is to rake up more! Both adults and children will enjoy this entertainment.
Painted in different colors the leaves look very picturesque. Collect beautiful bouquet from dried leaves: it will last a long time and will delight you, bringing a sunny mood to your home.
From recently fallen, still succulent leaves, you can assemble a colorful album with a herbarium. Place colorful leaves between the pages of an album or book. They will soon dry, and later, after flipping through the album, you will be able to inhale the aromas of autumn. 
The creation of such an album can be turned into an interesting and educational game for children. Collect different leaves, place them between the pages, and label which tree belongs to which leaf.
Any time of year is wonderful. Autumn gives us a rainbow of colors in parks, alleys and forests. Be open to such gifts and share them with your loved ones!
