Why do the leaves turn yellow? Trees and shrubs in autumn

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. Leaves even fall from evergreen plants 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 is not main reason leaf fall. The onset of unfavorable conditions is a signal for the transition of plants to a new life cycle, which is inherent in 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 big amount chlorophyll pigment contained in them. This pigment “feeds” the plants, since it is with its help that the plant synthesizes from carbon dioxide and water in the light organic matter and first of all, the main sugar is 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 acquire golden-red colors.

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 bound 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 nutrient synthesis in foliage also stimulates anthocyanin synthesis.

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 the organic matter formed by the plant. 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 useful properties fallen leaves. The first is to leave it in place until spring, followed by digging. In this case, the leaves will insulate the top layer of 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 we forget or don't know trivial things that we encounter every day. Such things include autumn leaf fall. In particular, quite respectable people often cannot explain why the leaves turn yellow and fall off in the fall. But we will try to do this without unnecessary scientific red tape. In doing so, you will learn some interesting factors behind this phenomenon.

Life cycles of trees

Let's start with the fact that a tree has several life cycles. This:

1. Summer;
2. Winter;
3. Autumn;
4. And spring periods.

So, in summer the plant actively develops. In the fall it prepares for winter, in the winter it goes into suspended animation, and in the spring it awakens, absorbing greatest number nutrients.

As part of the autumn cycle, leaf fall occurs. It is provoked by contraction daylight hours, cold and genetic set.

If everything is clear with cold and light, then the genetic setting is a signal to shed leaves no matter what. It is laid down at birth. And even if we have an eternal summer, the trees will still sleep for a couple of months. It is only possible that some of the leaves will still remain.

Why do leaves turn yellow and fall from trees?

The yellowing of everything and everyone occurs due to poor nutrition. The roots pump less liquid, and the sun does not allow active photo synthesis.

Thus, the green pigment chlorophyll is poorly produced. It is replaced by other pigments, such as carotene. And they are just yellow and crimson.

It is worth noting that yellowness is always present in the leaves. It’s just that in the summer it’s overwhelmed by chlorophyll.

And here’s another interesting thing: in the fall rainy weather leaves turn yellow less. And the sun just gives bright colors.

This is due to the fact that chlorophyll burns out when there is not enough of it. Therefore, ultraviolet light, which turns the foliage green in the spring, on the contrary, colors it in the fall.

Now about the fall of leaves. According to the genetic principle, a cork layer forms on tree branches with reduced nutrition. It seems to separate the stem of the leaf from the surface. As a result, the leaf falls when low pressure or under its own weight.

It is important to note that even fallen leaves contain many nutrients for insects. Therefore, from a biological point of view, it is wrong to throw away leaves.

Where did leaf fall come from?

In general, trees began to live in cycles due to global cooling. This phenomenon allows them to survive. The tree clogs the points left by the leaves. And the root begins to pump water much less.

Thus, there is a huge saving of nutrients. It makes it possible to fall asleep and survive the winter. Without leaf fall, this would have been impossible to do.

By the way, coniferous plants also have a kind of leaf fall. But it doesn't happen right away. Therefore it is difficult to see him. But if you look underneath coniferous plant, then you can also find a kind of carpet of “thorny leaves” there.

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Scientific Society of Students of MBOU Secondary School No. 15

Research work on the topic:

Why do leaves turn yellow in autumn?
and no indoor plants?

5 “b” class MBOU secondary school No. 15

Them. Hero Soviet Union Mildzikhova Kh.Z.

Head of work: Melikova R.N.

Teacher primary classes MBOU secondary school No. 15

Vladikavkaz, 2016

The plant continuously converts sunlight into energy and, thus, is an important link in the chain of life that spans the entire planet.

(slide – 2) With the arrival of autumn, I have always wondered: why do the leaves on trees and shrubs change color? Are they green in the summer and colorful in the fall? Why does leaf fall begin? What does it mean for plants?

I observed the trees and bushes, the “behavior” of the leaves. And for this I read several textbooks, books, encyclopedias.

And here's what I found out!

Plants are living chemical factories where complex reactions continually occur. The gas exchange that accompanies these reactions makes our planet suitable for life..(slide – 3) Most plants, from a tiny snowdrop to a giant tree, are similar in internal structure, despite the striking external differences. The conductive system through which nutrients circulate is a network of conductive bundles covering roots, stems and leaves.

There are two main types of cells in the vascular bundles. Water and mineral salts rise up from the roots through xylem cells, as if through channels. And phloem cells serve to transport the products of photosynthesis to places where they are needed.

(slide – 4) Photosynthesis is the biological process of converting radiant energy from the Sun into organic energy.

Three important processes occur in plants: photosynthesis, respiration and transpiration, or evaporation. Although the plant takes nutrients from the soil, it requires the process of photosynthesis.(slide – 5) Chlorophyll is the molecule that does all the work of breaking down carbon dioxide and water into oxygen and sugar (carbohydrates). His “workshop” - chloroplasts - color most plants the familiar green color.But besides chlorophyll, the leaves also contain other yellow and orange pigments - xanthophyll and carotene, the same as in carrots. And the leaves are colored in red, crimson shades thanks to the anthocyanin pigment, which is dissolved in the cell sap. But since the concentration of these pigments is less than chlorophyll, in the summer they are simply invisible on the leaves, because they are, as it were, masked by a large amount of chlorophyll. After all, it is in the summer, when the sun shines brightly and the daylight hours are longer, that the process of photosynthesis actively occurs and nutrients accumulate.

Sunlight is a stimulant chemical reaction in chlorophyll molecules, so without a sufficient supply of water, carbon dioxide and light, plant growth slows down ( slide – 6).

The development of plants and all phases of their existence are completely dependent on weather conditions - heat, humidity, sunlight.

From untimely or severe cold, the plant dies due to lack of moisture and cannot successfully develop its tissues; if there is an excess of it, it rots; from hot sun rays It will either get fried or completely dry out.

With the advent of unfavorable conditions, the process of colorful leaves falling off begins. deciduous trees and bushes.Deciduous trees include oaks, poplars, birches, lindens, maples, chestnuts, all fruit trees and many others, which are simply impossible to list - there are so many of them.

(slide – 7) Shrubs, like trees, also have tree-like stems. But they can’t find a trunk. Typically the shrub's stem branches just above the ground. We are familiar with lilac, currant, gooseberry, raspberry and rose hip.

2. Leaves of deciduous trees and shrubs in our area turn yellow and fall off. This phenomenon is calledleaf fall (slide – 8).Leaf fall has great importance for plants. The fact is that in winter there is much less moisture in the soil than in spring and summer. When the temperature drops below 5°, the roots stop absorbing water. And if the trees did not shed their leaves, this would lead to dehydration and death of the entire tree, because a lot of moisture evaporates from the surface of the leaves, which the tree has nowhere to take from. And the tree, in order not to die entirely, sacrifices its leaves. It stops sending water and salt to the leaves from the roots. This is why the leaves change color. The reason for the change in color of the leaves is that they contain coloring substances that appear depending on the amount of heat and light. In summer, the most active green substance is chlorophyll. In autumn, chlorophyll is destroyed, yellow and red substances appear, and the color of the leaves begins to change and the leaf falls off on its own.(slide – 9)

At the end of the cutting, which connects the leaf to the branch, a separating plate is formed. At this point the leaf separates from the branch. Try picking a leaf in spring or summer. This is quite difficult to do, since the leaf is firmly attached to the stem. But in the fall you can easily pick up whole bouquets of bright maple leaves. They fly away at the slightest touch or blow of wind.

Leaf fall is needed as good fertilizer. Plants can tell an observant person a lot.

For example, (slide 10 ) if a lot of sap flows from a birch tree in the spring, this means that the summer will be rainy. And the appearance on the trees in summer yellow leaves portends early autumn and vice versa.

(slide – 11) If the maple “cries”, it means that it will rain in a few hours. I have always been pleased and surprised by plants with beautiful colored leaves and flowers.

3. Houseplants, (slide – 12) They not only delight us with their beauty, but also cleanse the air of dust and dirt, enrich it with oxygen, and increase its humidity.

When placing purchased indoor plants in your apartment, you should remember that the well-being of everything depends on light, heat, humidity and watering.

If there is enough light, then the process of photosynthesis, which forms the basis of life, is activated in plants. Nutrients dissolved in water enter the leaves from the root system. Plants absorb carbon dioxide from the air and, as a result of a chemical process, release oxygen and produce complex organic substances.

In low light, this process slows down, and in the dark it stops completely. When placing plants indoors, it is important to consider the level of lighting. If the plant is on the window, (slide -13) it receives enough light, but as it moves away from the window, the intensity of the light decreases significantly. All plantsby light perceptiongrouped as:

Photophilous

Shade-tolerant

Unpretentious.

For the normal functioning of plants, a certaintemperature regime(slide – 14 ). It affects the process of photosynthesis and respiration, accelerates or slows down chemical processes and the flow of substances.

All plants according to heat demanddivided into three groups:

plants with a temperature of 10-12o

plants with a temperature of 13-20o

plants with a temperature of 21-25o

With sudden changes in air temperature, leaves dry out and fall off.

High temperatures and low air humidity cause leaves to fall.

With a lack of water, plant growth slows down, leaves turn yellow and curl, flowers fall off and buds fall off.

When there is excess moisture, the soil becomes acidic and a greenish coating appears on the surface. unpleasant smell, plant cuttings become moldy. Leaves and inflorescences rot.

A significant influence on the normal growth and development of many plants is exerted not only by heat, but alsoair humidity.

At low humidity air:

The edges of the leaves turn yellow;

The leaves wrinkle and wither.

At high humidity air:

Buds and flowers fall off.

For successful cultivation plants, it is necessary to select soil mixtures (light, medium, heavy).

4. After spending research work, I found out: (slide – 15)

With sudden changes in temperature, the leaves dry out and fall off.Trees get rid of leaves harmful products metabolism. Nutrients and essential mineral elements at the time of death, they almost completely pass from the leaves to the internal parts of the plants.

Too humid air leads to crust-like growths on the leaves and stem. The growth and development of plants is suspended.

As a result of observation, I noticed that not all trees and shrubs simultaneously change the color of their leaves.In autumn - winter time a period of relative dormancy begins, which lasts only 3-4 months in some plants or 5-6 months in others. During the dormant period, complex physiological and biochemical processes occur in plants that prepare the plants for active growth next year.

As for fertilizers, the plant must be watered before applying it so as not to burn the roots. And too concentrated a solution can lead to burns and death of plants. When preparing a nutrient solution, it is necessary to make it weaker.

The timing of fertilization largely depends on the species of the plant, its condition, age and time of year.

If we compare indoor plants with the plants that surround us on the street, then we can confidently say that we can influence indoor plants, correct their growth: spray, apply fertilizers, water less and vice versa, but with trees and shrubs we can only observe, analyze and draw conclusions(slide – 16)

Literature

1. Schoolchildren's reference book for primary grades (natural history) / N.A. Abelskaya, M.B. Eliseeva. – M.: AST; St. Petersburg: Sova, 2005. – 573, (3) S.: ill.
2. Vitaly Bianchi. Forest newspaper. Leningrad, 1963
3. Vorontsov V.V. Houseplants. New care guide. – M.: ZAO “Fiton+”, 2002. – 288S., ill.
4. The Tree of Knowledge - a universal illustrated reference book for the whole family No. 12, 2006. Animals and plants. Plant Physiology (pp. 41-44).

Which will clearly show children why the leaves on the reed trees change color: in the summer they are green, and in the fall they turn yellow.

To do this, you do not need special materials - everything is available both at home and at school. This experiment, which explains why the leaves on davy trees change color in the fall, is great for preschoolers and students in grades 1-6.

Many people consider it the most beautiful time of the year, because when the leaves turn yellow, nature turns into such incredible shades, which simultaneously preserve the memory of the warm summer, but evoke the cold of the approaching winter.

But children often have a number of traditional questions in the fall:

• Why do leaves on trees change color and turn yellow in autumn?
• Is this the tricks of fairies?
• What about the sun?
• Oh, I know, a garden gnome did it

This one, which explains why leaves turn yellow or red in the fall, is sure to satisfy even the most curious of children.

Why does a tree need leaves?

In order to understand why leaves change color in the fall, you need to understand why trees, and leaves in particular, are needed in the first place.

Plants are responsible for creating the oxygen we breathe. They produce it by absorbing water from the ground and carbon dioxide from the air. Using sunlight (through photosynthesis), they convert water and carbon dioxide into oxygen and glucose. Oxygen is what allows us to breathe, and glucose is what the plant uses to grow. The term photosynthesis means “to combine with light.” Chemical substance in a plant, what is used for photosynthesis is called chlorophyll. The same chlorophyll that gives plants green color.

What will you need for the experiment?:

• Glass jars
• Coffee filters
• Leaves
• Alcohol
• Notepad and pen for making observations

Why do leaves change color in autumn? Experiment for children

In order to find the answer to the question of why the leaves on trees change color and turn yellow in the fall, children will need to collect some leaves.

After which you must sort them together by color into prepared containers.

After this, the leaves are filled with alcohol and ground. Once crushed and stirred, the alcohol will help the color come out even better.

Tip: The time it takes for the color to fully absorb will depend on how much leaf and alcohol were used.

After 12 hours, the liquid may not yet be completely absorbed, but the effect is already obvious. As the liquid is absorbed into the filter, the colors from the leaves disperse.

Explanation of the experiment why leaves change color

In winter, the days become shorter, which reduces the number sunlight for leaves. Due to lack of sun, plants go into a dormant stage and feed on the glucose they accumulated over the summer. As soon as it turns on " winter mode", the green color of chlorophyll leaves the leaves. And as the bright green tint fades, we begin to see yellow and orange colors. Small amounts of these pigments were present in the leaves all along. For example, maple leaves bright red because they contain excess glucose.

If you liked the one with leaves that change color in the fall, you don't have to wait until school starts to do it with your kids.

Greetings, my dear researchers!

Today on discussion new project, the material on which may be useful to you for your next presentation in class “ The world" Why do leaves turn yellow in autumn? This question is often interesting for children, especially when they are walking along a park path, raking fallen leaves with their feet. But really, why?

Lesson plan:

What artist paints leaves?

In the summer, the green canopy of trees lives through a process called photosynthesis. Have you heard of this one?

I think it’s no secret even for preschoolers that leaves absorb carbon and process it using the energy of the sun into organic substances that they feed on, releasing oxygen back. This magic inside a tree leaf only happens when comfortable conditions: Warmth and sunlight are important to him. What is responsible for paints?

How do pigment neighbors live in leaves?

I see the question in my eyes: “Why, if all the pigments live together, there are no yellow and orange leaves in the summer, and green ones in the fall?

The thing is that active chlorophyll, with its large amount in warm weather, masks other dyes; they are simply not visible. With the onset of autumn, when there is little sun and daylight, the green artist begins to be produced less and less, no longer being replenished in such quantities as in the summer. That's when other shades begin to shine through.

That’s why very often, at the very beginning of autumn, the leaves on the tree are not all colored at once, but are painted in a bizarre pattern, when green veins still remain on the yellow or orange background.

Every day closer to winter, the existing chlorophyll is destroyed, new chlorophyll is not replenished due to the lack of conditions for photosynthesis. The veins of the leaves, through which nutrients flow, are closed with a dense plug of cells, reducing the amount of sap in the plant.

Here it is: golden autumn is in full swing, green leaves can no longer be found on the tree! Moreover, the faster the cold sets in, the sooner the tree “turns off” photosynthesis. A motley carpet appears under your feet, it’s time to curse a couple of times.

Why do trees shed leaves?

Yellow leaves are circling over the city,

With a quiet rustling they fall at our feet...

Indeed, they would stand all winter long, delighting us with their bright beauty. But no! Leaves begin to fall at our feet, heralding the change of season. Why?

With the arrival of cold weather, the soil begins to freeze, and the trees no longer have enough moisture and minerals. Life processes gradually fade away, all plants go into hibernation. How can you sleep if you need to feed every leaf? We have to save on food by getting rid of unnecessary consumers, which is why trees shed their leaves before winter.

At the place where the leaf petiole is attached, a special cork layer is formed, which blocks the flow of nutrients from the tree. The leaves hold on weaker and weaker every day and gradually fall off. As when changing color, they do not all leave the tree at once. Some will linger longer, fluttering in the wind, some will fall among the first, lining golden paths.

Therefore, leaf fall is a condition for the continuation of the life of a tree, necessary so that with the arrival of spring we can once again enjoy young green leaves.

This is how briefly we found the answer to the question posed today. To make the report interesting, I suggest a rebus on autumn theme. Catch it! And I say goodbye to you until we meet again on projects.

“On a stream, pockmarked and motley,

Poem - “Before the Rain”

Evgenia Klimkovich.