Why leaves turn yellow in autumn for children. Damage to the bark of garden trees in summer

A generous summer has passed, autumn has come. Its calendar beginning is September 1, astronomical - on the day of the equinox, September 23, and in nature, like spring, it comes in different dates. We encourage you to read with your children why do leaves turn yellow and fall from trees in autumn. The information will be useful for both little darlings and adults 😉

Birches turn yellow first

The first heralds of autumn are considered yellow leaves on birches. The mixed forests of the northern and temperate zones are becoming unrecognizable. Solid green summer coloring is replaced by bright multicolor. The leaves of hornbeams, maples and birches are now light yellow, oak - brownish-yellow, cherries, mountain ash, barberry - crimson, aspen - orange, and euonymus - purple.

Each tree is charming in itself, and their combination is fabulously beautiful. Not only trees are painted, but also shrubs and herbs. In the forest, their bright attire is less conspicuous, but in treeless places, shaggy motley carpets delight with multicolor.

Causes of autumn colors

It is known that the green color of the leaf depends on the green pigment - chlorophyll. But chlorophyll is not the only pigment in leaf cells. The leaves also have yellow, orange pigments - xanthophyll, carotene. By autumn, chlorophyll is destroyed; other pigments, previously masked by it, appear in all their glory, anthocyanin pigments develop, coloring the leaves in reddish and purple tones.

Leaf fall, leaf fall, yellow leaves fly ...

The wonderful dress of trees is short-lived. The leaf fall begins; this process is essential. And that's why. Leaves evaporate moisture, and in winter, water from the roots does not enter the crowns of trees. Leave the leaves on the tree, it would wither. In addition, the leaves, heavy with snow, would bend and break branches, which sometimes happens during early autumn snowfalls. Over the summer, a lot of mineral salts unnecessary for the plant accumulate in the leaves. When leaf fall, the plant gets rid of them. Finally, fallen leaves are fertilizer.

But why leaves so firmly held on the branches trees summer and so easy fall in autumn?

Even before the color of the leaves changes, their nutrients move to the branches, trunk, roots. At the same time, a layer of special thin-walled cells appears at the base of the leaf petiole, a kind of partition between the branch and the leaf petiole. The cells of this layer have smooth walls, and the connection between them is easily broken. The leaf by the beginning of leaf fall is kept on branches only thanks to vascular bundles. This connection is not strong. It is enough for abundant dew to fall, to blow in the breeze, and the leaf comes off.

After leaf fall, deep peace comes to the trees. At various plants it is of different duration. Poplar, lilac, bird cherry ends by December, oak, birch, linden lasts until February. Twigs cut from a tree during dormancy usually do not bloom in water.

Autumn is a capricious golden beauty!

wonderful gold autumn! She is sad and beautiful and at the time of withering. " sad time, eyes charm!

Here is the autumn meadow. It became wider, more spacious. In some places, yellow tansy, blue chicory inflorescences, wild pansies. And in October you can collect a modest bouquet.

And what a beautiful autumn dew! In autumn there is a lot of cobwebs, sometimes it forms whole walls between shrubs and tall grasses. The web behind the dew drops is not visible, and the drops seem to hang in the air.

Autumn white crispy matinees are amazing. Quiet. Everything is covered with frost, like shiny powdered sugar. Everything in nature breathes freshness, purity, vigor.

Autumn has its own unique flavor. The forest smells of mushrooms, and in the garden, even after harvesting apples, their smell lingers for a long time.

So much beauty in the naked forest! Leaves crunch underfoot. They do not know peace - they tremble, whirl on the ground, and caught up by the wind, they rush in its stream.

Capricious late autumn. Rarely does she give bright warm days. Increasingly, quietly crying with small drops of rain. Sometimes silent rain is suddenly replaced by a storm. An angry wind stirs the leaden clouds, tears the last leaves from the trees, bends the grass to the ground. But he's not terrible. Trees willingly give away the leaves they do not need, and grasses have long sent their seeds. The animals are not afraid of the cold wind either: they have prepared for the winter.

Winter is already on the lookout. The turn of winters has come. Snow suddenly falls. Once it will cover the earth, twice ... Each time it is more abundant. And it stays longer. At last the frost stopped the rivers. Autumn is over. Winter has come!

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In autumn, the green foliage of most plants changes color. Not only red, yellow, orange and bronze colors appear, but also brownish-gray shades. Sometimes on a sheet you can see summer and autumn colors at the same time. Even some conifers change the color of the crown. Specific weather conditions also largely influence this seasonal process.

Fall color of fallen leaves

What happens to the color of the foliage?

The green color of the leaves is associated with the presence of a green light-sensitive pigment. chlorophyll. Without it, plants will not be able to get food from water and carbon dioxide. Chlorophyll reserves are constantly replenished as long as there is light and heat. Actively goes photosynthesis process, in which organic substances such as starch and glucose are formed. With seasonal cooling, the accumulation of chlorophyll decreases, the process of photosynthesis slows down, the concentration of pigment in the leaves decreases sharply. Its cells are no longer able to receive and convert the energy of the sun, the pigment is destroyed. It is during this period that you can see leaves with a bizarre color: with green veins, strokes and spots on a yellow or red background.

In autumn, part of the foliage of Amur grapes remains green for some time.

In autumn, other pigments that are inside the cell sap of the leaf are more active. Carotenoids use those light spectra that chlorophyll does not perceive. They give the leaves a yellow xanthophyll pigment) and orange ( carotene pigment) coloring. Persistent pigments are responsible for the red tones anthocyanins. In summer, they are all replaced by chlorophyll, in autumn it is not a competitor to them. With a lack of pigments, grayish-brown tones appear.

Amur grapes are incredibly beautiful in autumn

Rainy and cloudy weather for some time slows down the process of destruction of chlorophyll. Separate sunny days they cannot bring back summer or stop the fading of life. Moreover, they only speed it up. illustrative example- , when green leaves behind a short time become crimson and gold, justifying our expectations of the Golden Autumn celebration.

Golden autumn gives way to leaf fall

Even with an autumn decrease in air temperature, some plants remain green. They are called evergreen. In our climate, these are conifers (except for larch) and a few deciduous trees and shrubs (some types of rhododendron, holly mahonia, boxwood, Fortune's euonymus, etc.). In warm countries evergreens a lot more.

The holly mahonia behaves interestingly, which for the winter I sometimes cover with a box that does not let light through. Then, by spring, it sheds all the leaves, its bright yellow flowers adorn completely bare branches. When insulated with lutrasil or without any shelter, this plant retains its foliage. In autumn, it changes color to reddish-brown, and in summer it becomes dark green again.

Some conifers (eg. certain types) in autumn change the color of the needles to golden or bronze. By the beginning of summer, the green color is restored.

leaf fall

A short period of elegant golden autumn gives way to leaf fall. Autumn cold is the cycle of plant life when chlorophyll is practically not formed. Leaves no longer receive nutrients. They become useless ballast, from which trees and bushes seek to get rid of. Along the way, there is a release from those harmful substances, which the leaves managed to accumulate over the summer.

A yellowed leaf on the ground is a symbol of autumn

During leaf fall, larch loses yellowed needles. In other conifers, the change of needles occurs less frequently: every year, every three to five years, less often after more years.

Leaf fall makes life easier for the plant in adverse conditions. Now he no longer needs to take care of the nutrition of the foliage.

Fallen leaves in autumn fruit trees don't always look good

There are many evergreens in warm regions. But even there there are deciduous crops. For example, a tree loses leaves in autumn not only in China and countries South-East Asia but also when grown indoors.

Ginkgo leaves turn golden in autumn

© Alla Anashina, website

Plants have long been proven to be living beings. They, like animals, eat, breathe, reproduce. There are thousands of bio chemical reactions, useful nutrients are formed, decay products are removed from them as a result of metabolism. That is, all the processes that characterize the manifestation of life are also present in plants that make our planet unimaginably beautiful, clean and diverse.

biological rhythms

How do plants breathe? Why do their leaves turn yellow? What do they eat? How do they grow? Many questions arise for those who see these amazing creatures, so diverse, beautiful, bright and colorful.

For all plants, certain characteristics are characteristic in the same way as for other living organisms. These include:

• opening and closing of buds under the influence of length and chemical composition environment;
• intensive growth of shoot mass;
• compression and opening of stomata on leaves;
• strengthening or weakening of respiration, photosynthesis;
• leaf fall and others.

Thus, the answer to the question of why the leaves of plants turn yellow lies in the mechanisms of biological rhythms. It is these processes that allow them to adapt to environmental conditions, survive in them, carry out their life activities as efficiently as possible, grow and develop, respond to chemical and physical influences from nature, humans, animals, and so on.

Why are the leaves on trees turning yellow? It is also one of the manifestations biological rhythm aimed at maintaining the viability of an individual in conditions of low temperatures and reducing the amount of sunlight and moisture. The color of the leaf blade is determined by special substances in its composition.

Why do leaves turn yellow and fall off? Yes, because there is a restructuring of chemical reactions inside the plant organism. Each representative of the flora contains in its composition a number of pigments - substances that determine the color of organs (leaves, corollas of flowers, stems, and so on). In total, four main groups of such compounds can be distinguished:

All of the above pigments primarily give an external reaction to a change in the state of individuals. Why do plants turn yellow leaves, which causes such manifestations, we will consider in more detail.

Causes of leaf fall in trees

The phenomenon of leaf fall is one of the most beautiful in nature. That is why autumn is the favorite season of many poets. After all, the surrounding beauty simply cannot but become a source of inspiration for creative people. Multicolor around, yellow, green, red, orange and even brown-violet shades just turn your head, and the smell of fallen leaves pleasantly pleases the sense of smell.

What caused such changes and is it always normal? Consider the causes of leaf fall in trees. They can be divided into two groups: natural and forced. Each includes a number of points and explanations for them.

Natural

These reasons include the seasonal change weather conditions, as well as a change in the length of daylight hours. All summer the green giants prepare for these rhythmic changes. They accumulate nutrients and store them in the stems and trunk, actively carry out the processes of photosynthesis and respiration, consume the maximum possible amount of moisture.

With the onset of cold weather, shortened daylight hours inside sheet plates transformations begin.

1. The pigment chlorophyll begins to act less and less, the color turns pale. This allows other pigments to show up. As a result, the leaves turn yellow, redden and so on. What will be the color of the falling leaves depends on the genetic characteristics of the tree species. Moreover, an interesting fact is that brighter sun in autumn time, the faster the chlorophyll is destroyed, and the leaves turn yellow. During prolonged rains, the trees delight with greenery longer.
2. During summer period many metabolic products, salts, minerals accumulate in the plates of the sheets. This makes the leaf heavy, and it gradually begins to exfoliate in the petiole from the stem.
3. At the base of the petiole, between it and the trunk, the processes of formation of a special tissue layer begin, gradually rejecting the leaf.
4. Under the influence of mechanical factors (rain, wind, thunderstorm, and so on), their own gravity, all the leaves begin to fall one by one.

Forced

There is another answer to the question of why the leaves turn yellow. This happens for forced reasons, such as:

Sometimes autumn appears before us in gray color. Gloomy leaden sky gray wall rain - it is easy to become discouraged. But there is also a bright spot to cheer up! 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 in the world with the synthesis of oxygen and other important substances from carbon dioxide and water. Chlorophyll is actively produced in the warm season, when trees get enough nutrients and moisture from the soil.

The oxygen obtained during the synthesis of the trees is released into the atmosphere, and the rest of the substances absorb themselves. With the onset of autumn, the activity of trees decreases, they receive less and less nutrition from the soil. The foliage continues to draw nutrients from the trunk to continue the process of photosynthesis. In turn, the tree, in order to preserve the reserves of substances during wintering, begins to take magnesium from the leaves, which leads to the destruction of chlorophyll. As soon as the green pigment begins to break down, other shades appear. Why is one leaf red, the other yellow, and the third motley, like an artist's palette? Turns out it's a matter of chemistry.

What determines the color of the leaves

• We can see the yellow color due to the xanthophyll pigment.
• Carotene is responsible for the orange color.
• Crimson and red leaves become 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 production of chlorophyll green color overrides all others. But the leaf becomes brown or brown already when it completely loses coloring pigments. At this time, empty cell walls become visible to us, which have a brown color.

When leaves change color

As a rule, the color of the foliage changes in autumn, because it is at this time of the year that the level of vital activity of plants decreases. It is getting colder outside, and the trees are getting less and less nutrients from the soil. Chlorophyll starts to break down.
At the same time, its most active destruction occurs in the light. If the weather outside is cloudy and rainy, then oaks, maples, birches will remain green longer. If there are clear sunny days outside, then the trees will change their color much faster.

In hot and dry summers, when plants lack moisture and there is plenty of sunlight, leaves can also lose chlorophyll and green color.

What happens in autumn with conifers

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 keep them alive.

But even conifers lose their needles, it only happens gradually. The needles are not replaced at the same time, but in parts.

Capture and save the bright moments of autumn

Colored foliage remains in forests and parks for a very short time, the activity of plants 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. It will take quite a bit of time, 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 memory. A pleasant autumn pastime is a walk through a colorful forest or park, when soft leaves of juicy shades rustle under your feet. Only at this time of the year you can find a special silence in the forest, when the rustle of leaves is clearly audible.

Unforgettable sensations will be given by a running jump into a soft pile of multi-colored freshly fallen leaves, the main thing is to warm up more! Such entertainment will appeal to both adults and children.

Painted in different colors the leaves look very pretty. Gather beautiful bouquet from dried foliage: it will stand for a long time and will delight you, bringing a sunny mood to the house.

From recently fallen, still juicy leaves, you can assemble a colorful album with a herbarium. Put colorful leaves between the pages of an album or book. They will soon dry, and later, when you flip through the album, you can breathe in the aromas of autumn.

The creation of such an album can be turned into an interesting and educational game for children. Collect different leaves, arrange them between the pages, and label which tree belongs to which leaf.

Any time of the year is great. Autumn gives us a rainbow of colors in parks, alleys and forests. Be open to such gifts and share them with your loved ones!

Leaves are green in summer due to a large number the chlorophyll pigment they contain.

This pigment is the plant's breadwinner, since it is with its help that in the light the plant synthesizes the main sugar, glucose, from carbon dioxide and water, and from it all other nutrients.

However, along with chlorophyll, green leaves also contain other pigments - yellow xanthophyll and orange carotene (the one that determines the color of carrot roots).

In summer, these pigments are invisible, as they are disguised large quantity chlorophyll. In autumn, as the vital activity in the leaf dies out, chlorophyll is gradually destroyed. This is where the yellow and red shades of xanthophyll and carotene appear in the leaf.

The destruction of chlorophyll is more intense in the light, that is, in sunny weather. That's why on a cloudy rainy autumn leaves keep their green coloring. But if to replace long rains“Indian summer” comes, then the crowns of trees in 1-2 days are painted in the golden colors of autumn.

In addition to gold, the autumn dresses of trees contain crimson hues. This color is due to a pigment called anthocyanin. Unlike chlorophyll, anthocyanin is not bound inside the cell with plastic formations (grains), but is dissolved in the cell sap. With a decrease in temperature, as well as in bright light, the amount of anthocyanin in the cell sap increases. In addition, stopping or delaying the synthesis of nutrients in the foliage also stimulates the synthesis of anthocyanins.

Thus, the red color of the leaves during leaf fall simply indicates the ongoing attenuation of vital activity in the leaves, which are preparing to fall ...

Why do trees shed their leaves in autumn?

If the trees did not shed their leaves for the winter, they would die. There are several reasons for this.

Reason one. The leaves of the tree in their totality have very large area, and water is rapidly evaporating from all this area. In summer, the tree is able to compensate for the loss of moisture by extracting water from the soil. But with a cold snap cold water from the soil is greatly reduced; in winter, it is completely difficult to extract moisture from frozen soil. Trees with deciduous cover in winter would die from lack of moisture, that is, they would dry out.

For the same reason, with the onset of the dry season in the tropics and subtropics, the trees in these climatic zones shed their leaves and stand bare until the rainy season arrives.

The second reason. Have you noticed that after heavy snowfalls, the branches of trees strongly lean towards the ground under the weight of snow? Some branches even break from it. If the leaves remained on the trees in winter, then much more snow would linger on the branches, since the leaf surface, as we said above, is large. Thus, dropping leaves in autumn, trees protect themselves from mechanical damage under the pressure of snow.

Reason three. During leaf fall, the tree gets rid of excess mineral salts that accumulate in the leaves throughout the summer. As we have repeatedly noticed, the sheet intensively evaporates water. To replace this evaporated water, new water constantly enters it, which is sucked in by the roots from the soil. But in the water that the roots get from the soil are dissolved various salts. So the leaves don't get clean water, a saline solutions. Part of the salts is used by the plant for nutrition, and the rest of the salts are deposited in the cells of the leaves. The more moisture the leaf evaporates, the more it mineralizes by autumn. As a result, by autumn, the leaves accumulate a lot of salts, becoming, as it were, mineralized. An excess of mineral salts disturbs normal work leaves. Therefore, shedding old leaves is necessary condition to keep the plant alive.

By the way…

How do conifers manage not to lose moisture in winter, while remaining green? The secret is that the needles evaporate many times less moisture than the leaves. Firstly, the surface of the needle is many times smaller than the surface of the leaf; secondly, the needles have a thick skin; thirdly, they are covered with a wax coating, which also reduces the evaporation of water. Finally, the stomata in the needles are located in special recesses - this reduces the intensity of moisture evaporation through them.
Coniferous trees also shed their cover, but not at once, as they do hardwoods, but gradually: coniferous needles live, on average, 3-4 years. Therefore, the change of "clothes" of conifers goes unnoticed.

How do trees shed their leaves?

Leaf fall is a natural stage in the life cycle of a plant. Autumn dropping of leaves is not a direct consequence of the deterioration of weather conditions, this is a hereditarily fixed property of the plant. The signal for the beginning of leaf fall is not a drop in temperature, as one might think, but a change in the length of daylight hours - the surest and invariable sign of the onset of autumn. This is confirmed by a very simple experiment. If in the summer some young deciduous tree, for example, an oak or a maple, is transplanted into a pot with earth, and placed in a room or in a greenhouse, in the autumn it will inevitably shed its leaves, despite the most best care and warm.

Nature made sure that the parting of a tree with a leaf was painless for him. Preparation for leaf fall begins in advance. At the end of summer, a special separating (cork) layer forms at the base of the leaf petiole. The cells of this layer have smooth walls and therefore can easily separate from each other.

In autumn, by the beginning of leaf fall, the connection between the cells of the cork layer is broken. The leaf remains hanging on the tree only thanks to the vascular bundles that connect the leaf to the branch. In summer, these bundles serve to carry water and mineral salts from the root to the leaves and nutrients produced by the leaves to the rest of the plant. Vascular bundles can be easily seen with the naked eye on leaf scars in the form of three, five or more large dots.

A small mechanical action, such as a gust of wind, is enough to break this last connection between the leaf petiole and the mother plant. Leaves can also fall off in completely calm weather under the influence of the gravity of the leaf blade.

In place of the scar from the torn off sheet, a protective cork layer is formed.