Plant roots: morphology, functions, taproot and fibrous root systems. What are the main functions of roots in plant life? Basic functions of the root

One of the most important parts of the plant is the root. It is this that ensures the normal functioning of trees, grasses, shrubs and even aquatic flora. Often the above-ground part of the plant is just the tip of the iceberg. Most of it may be underground. It is no coincidence that the roots are so large, because they have very important functions. Let's take a closer look at the amazing features of the plant world.

Functions of roots

The roots of each plant perform a range of tasks that may vary from species to species, but in most cases these tasks are the same for both trees and their smaller relatives. The roots of trees and other above-ground plants help them stay upright and resist wind and animals. This is especially true for large trees due to their mass and height. The root system helps them attach to the bottom and also prevents some of them from flipping over.

Another function of roots is nutritional. They absorb water from and from the soil and deliver it to the right places. They also synthesize some amino acids, alkaloids and other elements that plants need. Some of the representatives of the flora generally store useful substances directly in the roots (mainly starch and other carbohydrates). Also, do not forget about such a thing as mycorrhiza - a symbiosis of a plant with fungi. The root plays a key role in it. such that some plants reproduce with its help - by root suckers.

Types of roots

Depending on the structure and function assigned to them, there are different types of roots. The first one is the main one. It grows directly from the seed when it germinates, to then become the main axis of the entire root system. In addition to the main root, there are also subordinate roots. They form from a variety of places - on stems, sometimes on leaves, and in some cases even on flowers. Another type is lateral roots. They emerge from the main or adventitious roots and branch laterally, forming more and more shoots.

Root systems

All the roots that the plant has form the root system. Depending on the role of various roots in the life of their owner, two types of systems are distinguished - taproot and fibrous. The first is distinguished by its focus on the main root, which grows most intensively. In this type, the main core develops much more efficiently than the side ones. However, this difference can be seen mainly in initial stage growth. Over time, the lateral roots begin to inexorably catch up with their main brother, and in old plants they are even larger than the main one. The rod system is typical mainly for

The second type is distinguished by features of the root opposite to the tap root. Such a system is called fibrous. It is characteristic of and distinguished by its numerous adventitious and lateral processes that fill the space under the plant. In this case, the main root is usually poorly developed or practically undeveloped.

Root. Root structure

Each root is divided into several zones, each of which is responsible for its own unique functions. One of the most important places is the division zone. It is located at the tip of each root and is responsible for its growth in length. Here, myriads of small cells constantly multiply. This process allows this part of the root to perform its difficult task. But the division zone is useless without the root cap, which is located at the end of each root. It consists of layers of fused cells that protect dividing cells from mechanical damage. In addition, the root cap secretes a kind of mucus that promotes the advancement of roots in the soil.

The next segment of the root is the elongation zone. It is located immediately behind the division area and is distinguished by the fact that its cells are constantly growing, although the process of division is almost completely absent in them. Then there is the suction zone - the place where water and minerals are drawn from the soil. This happens thanks to the myriads of tiny hairs covering this area. They significantly increase total area absorption. At the same time, each hair works like a pump, sucking everything necessary from the soil. Next comes the conduction zone, which is responsible for transporting water with minerals to the top. Also from here the elements responsible for the vital activity of the root system descend. This part is very strong and it is from it that the lateral roots grow.

Cross section

If you cut the root, you can see the layers that make it up. First comes the skin, which is only one cell wide. Under it you can see the base of the root - the parenchyma. It is through its loose tissue that water and minerals enter the axial cylinder. It is formed by the pericambium - the educational structure that usually surrounds

Around the conducting cylinder there are tightly closed endodermal cells. They are waterproof, which forces life-giving moisture with minerals to move upward. But how then does the liquid get inside? This occurs thanks to special passage cells located on the endoderm. In most cases, the roots of grass, trees, and shrubs have this structure, although sometimes there are differences.

Mycorrhiza

Often, the roots of trees are the site of their symbiosis with other life forms. Fungi become the most common partners of plants.

This phenomenon is called mycorrhiza, which stands for “fungus root.” It's hard to believe, but most trees depend on a fruitful union with mycelium. Our usual birches, maples and oaks benefit greatly from this symbiosis.

When the mycelium interacts with the roots, an exchange occurs in which the mycelium gives essential minerals to the tree, receiving carbohydrates in return. This evolutionary move has allowed many plant species to live in conditions unsuitable for their species. Moreover, some representatives of the flora would not exist at all if it were not for mycorrhiza. In addition to symbiosis with fungi, there is a beneficial cooperation with bacteria, which the root resorts to. The structure of the root in this case will differ from what we are used to. On it you can find nodules in which special bacteria live, supplying the tree with atmospheric nitrogen.

Conclusion

One of the most important parts of any plant is the root. The structure of the root is ideally suited for the tasks it performs. The root system is an amazing mechanism that nourishes plants. It is not for nothing that various mystical movements believe that the tree combines the powers of heaven and earth. Its above-ground part absorbs sunlight, and the roots receive nutrition from the soil.

The significance of the root system is not obvious, since the main attention is drawn to the above-ground part of the plant: foliage, trunk, flower, stem. At the same time, the root remains in the shadows, modestly fulfilling its honorable mission.

Questions:
1. Root functions
2.Types of roots
3.Types of root system
4. Root zones
5. Modification of roots
6. Life processes at the root

1. Root functions
Root- This is the underground organ of the plant.
Main functions of the root:
- supporting: roots anchor the plant in the soil and hold it throughout its life;
- nutritious: through the roots the plant receives water with dissolved minerals and organic substances;
- storage: nutrients can accumulate in some roots.

2. Types of roots

There are main, adventitious and lateral roots. When a seed germinates, the embryonic root appears first and turns into the main one. Adventitious roots may appear on the stems. Lateral roots extend from the main and adventitious roots. Adventitious roots provide the plant with additional food and perform a mechanical function. They develop when hilling, for example, tomatoes and potatoes.

3. Types of root system

The roots of one plant are the root system. The root system can be taprooted or fibrous. The taproot system has a well-developed main root. Most dicotyledonous plants (beets, carrots) have it. U perennial plants The main root may die, and nutrition occurs through the lateral roots, so the main root can only be traced in young plants.

The fibrous root system is formed only by adventitious and lateral roots. It does not have a main root. Monocot plants, for example, cereals and onions, have such a system.

Root systems take up a lot of space in the soil. For example, in rye, the roots spread 1-1.5 m wide and penetrate up to 2 m deep.

4. Root zones
In a young root, the following zones can be distinguished: root cap, division zone, growth zone, suction zone.

Root cap has a darker color, this is the very tip of the root. The cells of the root cap protect the root tip from damage by solid soil particles. The cells of the cap are formed by the integumentary tissue and are constantly renewed.

Suction zone has many root hairs, which are elongated cells no more than 10 mm long. This zone looks like a cannon, because... root hairs are very small. Root hair cells, like other cells, have cytoplasm, a nucleus and vacuoles with cell sap. These cells are short-lived, die quickly, and in their place new ones are formed from younger surface cells located closer to the tip of the root. The task of root hairs is to absorb water and dissolved nutrients. The absorption zone is constantly moving due to cell renewal. It is delicate and easily damaged during transplantation. The cells of the main tissue are present here.

Venue area . It is located above the suction, has no root hairs, the surface is covered with integumentary tissue, and in the thickness there is conductive tissue. The cells of the conduction zone are vessels through which water and dissolved substances move into the stem and into the leaves. Here there are also vascular cells through which organic substances from the leaves enter the root.

The entire root is covered with mechanical tissue cells, which ensures the strength and elasticity of the root. The cells are elongated, covered with a thick membrane and filled with air.

5. Modification of roots

The depth of root penetration into the soil depends on the conditions in which the plants are located. The length of the roots is affected by humidity, soil composition, and permafrost.

Long roots form in plants in dry places. This is especially true for desert plants. Thus, the root system of camel thorn reaches 15-25 m in length. In wheat on non-irrigated fields, the roots reach a length of up to 2.5 m, and on irrigated fields - 50 cm and their density increases.

Permafrost limits the depth of root growth. For example, in the tundra, the roots of a dwarf birch are only 20 cm. The roots are superficial and branched.

In the process of adaptation to environmental conditions, plant roots changed and began to perform additional functions.

1. Root tubers act as storage nutrients instead of fruits. Such tubers arise as a result of thickening of the lateral or adventitious roots. For example, dahlias.

2. Root vegetables - modifications of the main root of plants such as carrots, turnips, and beets. Root crops are formed bottom stem and the upper part of the main root. Unlike fruits, they do not have seeds. Root crops are biennial plants. In the first year of life, they do not bloom and accumulate a lot of nutrients in the roots. On the second, they quickly bloom, using the accumulated nutrients and forming fruits and seeds.

3. Trailer roots (suckers) are adventitious roots that develop in plants in tropical areas. They allow you to attach to vertical supports (to a wall, rock, tree trunk), bringing the foliage to the light. An example would be ivy and clematis.

4. Bacterial nodules. The lateral roots of clover, lupine, and alfalfa are peculiarly modified. Bacteria settle in young lateral roots, which promotes the absorption of gaseous nitrogen from the soil air. Such roots take on the appearance of nodules. Thanks to these bacteria, these plants are able to live in nitrogen-poor soils and make them more fertile.

5. Aerial roots are formed in plants growing in humid equatorial and tropical forests. Such roots hang down and absorb rainwater from the air - they are found in orchids, bromeliads, some ferns, and monstera.

Aerial buttress roots are adventitious roots that form on tree branches and reach the ground. Occurs in banyan and ficus trees.

6. Stilt roots. Plants growing in the intertidal zone develop stilted roots. They hold large leafy shoots on unstable muddy soil high above the water.

7. Respiratory roots are formed in plants that lack oxygen for respiration. Plants grow in excessively moist places - in marshy swamps, creeks, sea estuaries. The roots grow vertically upward and reach the surface, absorbing air. Examples include brittle willow, swamp cypress, and mangrove forests.

6. Life processes at the root

1 - Absorption of water by roots

The absorption of water by root hairs from the soil nutrient solution and its conduction through the cells of the primary cortex occurs due to the difference in pressure and osmosis. Osmotic pressure in the cells forces minerals to penetrate into the cells, because. their salt content is less than in the soil. The intensity of water absorption by root hairs is called suction force. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in dry soil conditions, as well as with excessive application. mineral fertilizers. Root pressure can be confirmed through a series of experiments.

A plant with roots is lowered into a glass of water. Pour a thin layer over the water to protect it from evaporation. vegetable oil and mark the level. After a day or two, the water in the tank dropped below the mark. Consequently, the roots sucked up the water and brought it up to the leaves.

Goal: find out the basic function of the root.

Cut off the stem of the plant, leaving a stump 2-3 cm high. Place it on the stump rubber tube 3 cm long, and at the upper end we put a curved glass tube 20-25 cm high. The water in the glass tube rises and flows out. This proves that the root absorbs water from the soil into the stem.

Goal: find out how temperature affects root function.

One glass should be with warm water(+17-18ºС), and the other with cold (+1-2ºС). In the first case, water is released abundantly, in the second - little, or stops altogether. This is proof that temperature greatly influences root function.

Warm water is actively absorbed by the roots. Root pressure increases.

Cold water is poorly absorbed by the roots. In this case, root pressure drops.

2 - Mineral nutrition

The physiological role of minerals is very great. They are the basis for synthesis organic compounds and directly affect metabolism; act as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are centers of electrical and radioactive phenomena in plant organisms. The root provides mineral nutrition to the plant.

3 - Root Breathing

For normal growth and development of the plant, it is necessary that the root receives Fresh air.

Goal: check for breathing at the roots.

Let's take two identical vessels with water. Place developing seedlings in each vessel. Every day we saturate the water in one of the vessels with air using a spray bottle. Pour a thin layer of vegetable oil onto the surface of the water in the second vessel, as it delays the flow of air into the water. After some time, the plant in the second vessel will stop growing, wither, and eventually die. The death of the plant occurs due to a lack of air necessary for the root to breathe.

It has been established that normal plant development is possible only if there are three substances in the nutrient solution - nitrogen, phosphorus and sulfur and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual meaning and cannot be replaced by another. These are macroelements, their concentration in the plant is 10-2–10%. For normal plant development, microelements are needed, the concentration of which in the cell is 10-5–10-3%. These are boron, cobalt, copper, zinc, manganese, molybdenum, etc. All these elements are present in the soil, but sometimes in insufficient quantities. Therefore, mineral and organic fertilizers are added to the soil.

The plant grows and develops normally if the environment surrounding the roots contains all the necessary nutrients. This environment for most plants is soil.

§ Absorption of water and minerals. The entry of soil solution into the root occurs through root hairs. The hairs actively influence the soil contents, releasing various substances that facilitate the selective absorption of ions from the soil. Since the concentration of minerals in cell sap is higher than in the soil solution, water with mineral salts dissolved in it in the form of ions enters the root hairs. The role of a pump in the root hair is performed by vacuoles, in which a higher concentration of salts is created than in the soil. The entry of mineral salts into the root occurs due to the active transport of anions and cations, which are part of the membranes using the energy of ATP. In this case, an exchange of ions can occur between the soil and the roots. Since the concentration of cell sap in the vacuole is higher than the concentration of the soil solution, water rushes into the cell during the process of diffusion. From the root hairs, water moves according to the same principle into the cells of the parenchyma of the cortex and through the passage cells of the endoderm enters the vessels. The force that drives the flow of water to the vessels and into all organs is called root pressure. According to hydrostatic laws, the value of turgor pressure (T) in all parts of the cell is the same, therefore the suction force (S) is greater in the part where the osmotic pressure (P) is greater. This law can be expressed as a formula:

S = P - T, where S is the suction force; P - osmotic pressure; T - turgor pressure.

The reverse flow of liquid is prevented by endodermal cells with dense membranes, which do not allow substances dissolved in water to pass back into the soil, creating a high concentration of cell sap in the central cylinder. Thus, the movement of water and salts dissolved in it is facilitated by the suction force of root hairs, root pressure, the adhesion force between water molecules and the walls of blood vessels, as well as the suction force of leaves, which, constantly evaporating water, attract it from the roots.

§ The second main function of the root is to strengthen plants in the soil, which occurs due to the branching of the main root. The branching of the main root is called lateral roots. They are formed (endogenously) in the pericycle and come out through the primary cortex. As the main root grows, lateral roots of the first order appear, which subsequently branch and form second-order roots, and from them third-order roots are formed, etc. Root branching helps strengthen the plant in the soil and increase the absorbent surface of the root. Other root functions include the following.

§ Synthesis of organic substances.

§ Supply of nutrients Such roots become very thick and act as a reserve of nutrients.

§ Due to the roots, plants communicate with bacteria and fungi. The root releases various substances into the soil and enters into symbiosis with fungi and bacteria.

§ Vegetative propagation is carried out using roots.

Root Breathing is of great importance for the normal functioning of the plant. The set of processes that ensure the entry of oxygen into the plant and the removal of carbon dioxide, as well as the use of oxygen by cells and tissues for the oxidation of organic substances with the release of energy necessary for the life of the plant, constitutes respiration. Respiratory energy is necessary for the intake, transport and synthesis of substances. From organic compounds coming from leaves and mineral salts from the soil, many vital substances are synthesized in root cells: amino acids, enzymes and phytohormones, etc. Carbon dioxide formed during respiration is involved in the metabolism and supply of substances to the root. Roots of many wild plants able to tolerate anaerobic (oxygen-free) conditions. Majority cultivated plants- Aerobes and their respiration are preceded by hydrolysis (conversion of polymers into monomers) and oxidation of organic substances. Breathing is a multi-stage process. When breathing occurs in cells, oxygen oxidizes a number of substances (mainly carbohydrates) and energy is released. necessary for plants for growth, movement of protoplasm, movement of substances. Respiration is the opposite process of photosynthesis. During photosynthesis, a plant absorbs carbon dioxide and water and produces sugars. During respiration, sugars are oxidized and carbon dioxide and water are formed:

photosynthesis

6(CO 2 +H 2 O) C 6 H 12 O 6 +6O 2

When one gram of sugar molecule is oxidized during respiration, 674 kcal of energy is released. The released energy is spent on a variety of biochemical and physical processes: the synthesis of organic substances, the movement and absorption of solutions, the growth and movement of organs. The plant releases part of the energy released during respiration in the form of heat. Breathing is especially vigorous at the growth points of the root. An increase in the amount of oxygen in the air, as well as a slight decrease in its content, does not affect the intensity of breathing, and only a decrease in the oxygen content in the air by 10-20 times compared to normal weakens breathing. The root carries out its functions of providing the plant with nutrients only when there is a sufficient amount of air in the soil. Therefore, when growing plants, you need to ensure that fresh air is constantly supplied to the roots. To do this, the soil is regularly loosened with cultivators or hoes. Loosening the soil also helps retain moisture in dry areas. When the soil dries out, a crust forms on its surface: it promotes rapid evaporation of water. During loosening, the crust is destroyed and surface layer moisture is retained. Water stops evaporating from deeper layers of soil. It’s not for nothing that loosening is sometimes called “dry watering.” They say: “It’s better to loosen well once than to water poorly twice.” A number of tropical swamp plants (mangrove forests) develop respiratory roots during the process of evolution. They rise vertically upward, there are holes on their surface through which air enters the roots, and then into parts of the plant immersed in swampy soil.

The soil- this is the parent (soil-forming) rock, processed by the combined action of climate, plant and animal organisms, and in cultivated areas and human activity, capable of producing plant crops. The main property of soil is fertility - the ability to satisfy the needs of plants for nutrients, water, air, heat for their normal life and production of crops. Soil differs from rocks, sand or clay in the presence of humus. Soil fertility depends mainly on soil structure and humus reserves. The ability of soil to form lumps of various sizes and shapes is called soil structure, and the lumps themselves are called structure. Depending on the presence of structural elements, soils can be structured or structureless. Well-structured soil provides favorable water-air properties. The composition of the soil includes sand, clay and other insoluble minerals, as well as soluble minerals and humus. Soil also contains air and water.

Humus(humus) is a complex complex of organic substances formed in the soil during the decomposition of plant and animal residues. The thicker the top layer of soil containing humus, the more fertile it is. The most fertile are humus-rich chernozems and dark meadow soils of river floodplains. Podzolic, clayey and sandy soils have no structure and are poor in humus, therefore less fertile.

Depending on the content of small (clayey) or larger (sandy) particles in the soil, soils are divided into light sandy, sandy loam, loamy and clayey.

The productivity of cultivated crops depends on soil fertility. Cultivated lands are the result of complex natural labor processes of many generations of people. Some human impacts on the soil lead to an increase in their fertility, while others lead to deterioration, degradation and death. To especially dangerous consequences human influence on the soil should include erosion, pollution by alien chemicals, salinization, waterlogging, soil removal for various structures (transport highways, reservoirs). The decrease in the area of ​​fertile soils occurs many times faster than their formation. Soil protection should be of an environmental, resource-saving nature and provide for their conservation. To provide rational use lands in Russia, the State Land Cadastre is maintained, which contains information on lands of all categories. The cadastre was adopted in 2001, it carries out the following main activities:

1) exercises control over the use and protection of lands;

2) conducts land monitoring;

3) identifies contaminated and degraded lands, prepares proposals for their restoration and conservation.

Of great importance is the introduction of soil-protective plowless cultivation, which slows down nitrophification processes in the soil, reduces the pesticide load, reduces the nitrate content in agricultural products, and also accelerates the restoration processes of humification of organic matter.

Land monitoring is a system of monitoring the state of the land fund for the timely identification and assessment of changes, prevention and elimination of the consequences of negative processes. Land monitoring was approved in 1992 and is integral part environmental monitoring.

Our country has adopted a Land Law. It provides for measures to increase soil fertility and protect it. Improper use of soil and failure to comply with the rules for growing crops can lead to destruction of the soil structure, soil erosion, salinization and waterlogging. All this worsens soil fertility and reduces yield. That is why it is important to carry out land reclamation (improvement).

Fertilizers. Plant organisms consist of organic and inorganic substances, which contain various chemical elements. For normal plant development, roots must deliver water and mineral salts, macroelements (P, N, K, Ca, Mg, Fe) and microelements from the soil
(B, Cu, Mn, Zn, Mo). It is known that nitrogen is part of amino acids, proteins, ATP, ADP, vitamins, and enzymes. Its deficiency retards plant growth. Phosphorus is part of ATP and ADP, amino acids, enzymes; Potassium affects the state of the cytoplasm, the osmotic pressure of cell sap, and also affects plant growth. Macro- and microelements are of great importance for plant life. Each element has an individual meaning and cannot be replaced by another. With a deficiency or excess of any mineral element in the soil, various disturbances in the vital processes of plants occur. Thus, during phosphorus starvation in plants, suppression of synthesis and breakdown of previously formed proteins is observed. The lack of potassium stops plant growth, as the metabolism of proteins and carbohydrates is disrupted. Iron deficiency is indicated by a pale green or pale yellow color due to insufficient chlorophyll production. Mineral salts containing both macro- and microelements are formed in the soil after the mineralization of organic matter, the dissolution of minerals, and the absorption of certain elements from the atmosphere by the soil. Macro- and microelements are found in fertile layer soils in the composition of various compounds. All of the above elements are present in the soil, but sometimes in insufficient quantities. Every year, plants remove nutrients from the soil, the soil is depleted, which reduces the yield of agricultural plants. To improve mineral nutrition, fertilizers are applied to the soil. By using fertilizers, a person actively interferes with the cycle of substances in nature, creating a balance of nutrients in the soil. Fertilizers are applied to the soil in certain doses at certain times, which improves the quality of the soil and plant nutrition.

There are organic, mineral, mixed, green, and bacterial fertilizers.

Organic fertilizers(manure, peat, bird droppings, slurry, sapropel, etc.). They contain nutrients in the form of organic compounds of plant and animal origin. Organic fertilizers are applied to the soil in advance, usually in the fall, since they decompose slowly and can provide plants with mineral nutrition elements for a long time. Organic fertilizers are complete; they contain both macro- and microelements. In addition, they improve the physical properties of the soil: they increase its structure, increase water permeability, water-holding capacity, improve aeration, thermal conditions, and activate the activity of microorganisms inhabiting the soil.

Mineral fertilizers Most often they contain one or two batteries, less often - more, then they are called complex. Mineral fertilizers decompose in the soil easier and faster than organic ones.

Depending on the content of mineral substances, nitrogen, phosphorus and potassium mineral fertilizers are distinguished.

To nitrogen fertilizers include: nitrates - potassium, calcium and sodium nitrate (nitrogen in the form of NO ammonium).

TO potash fertilizers include: potassium salts (sylvinite, kainite, carnallite); concentrated potash fertilizers (potassium chloride, potassium sulfate, etc.).

Phosphorus fertilizers- superphosphate, phosphate rock, slag. Mixed fertilizers include organomineral fertilizers - humates, humoammophos, nitrogumates, mixtures of organic and mineral fertilizers, often composted or made in the form of granules. These are mainly products of chemical treatment of organic substances (peat), ammonia, nitric or phosphoric acid.

Mineral fertilizers are introduced into the soil in a strictly defined dose and at a certain time. Each mineral fertilizer has its own specific characteristics. Therefore, in the spring, during the growth period, the plant needs nitrogen, as it promotes the accumulation of vegetative mass, an increase in chlorophyll and photosynthesis. By the time of budding and flowering, the need for phosphorus and potassium increases, since phosphorus, potassium and magnesium affect the construction of new cells in embryonic tissues (seed). Potassium has a particularly beneficial effect on the formation of seeds and fruits. Taking into account the different needs of plants for mineral nutrition elements in different phases of development, fertilizers are applied not only before sowing, but also during the growing season in the form of fertilizing, sometimes when sowing in rows. Recently, a method has become widespread foliar feeding, where liquid fertilizer is sprayed directly onto plants, often from airplanes. Dissolved nutrients are absorbed by the leaves. This method is especially convenient for the use of microelements, since it ensures uniform application of solutions to plant leaves and more economical use of scarce fertilizers.

Green fertilizers. In areas that require organic fertilizers, crops such as lupine, seradella, alfalfa, peas, clover, buckwheat, mustard, etc. are grown. During the period of greatest green mass, they are plowed. When plants decompose, organic matter is formed in the soil.

Bacterial fertilizers. These include nitragine. It is added when sowing seeds leguminous plants. For different cultures They use specific forms of nitragine, since races of nodule bacteria that develop on the roots of one species cannot live on the roots of other species. Azotobacterin, containing a culture of Azotobacter, is specific for individual species cultivated plants. Phosphorobacterin is a preparation containing bacteria that mineralize organic compounds of phosphoric acid. Boron, copper, manganese, molybdenum, zinc and cobalt compounds are used as microfertilizers.

Doses of organic and mineral fertilizers depend on the nutrient content in the soil and the individual needs of the plant. Too much fertilizer in the soil is just as harmful as too little. Irrational use of fertilizers causes serious harm not only to plants, but also to the soil and can ultimately lead to increased acidity, salinity, and, consequently, loss of fertility. Excessively applied fertilizers accumulate in agricultural products and have a harmful effect on the human body.

The importance of tillage. Tillage is mechanical impact on the soil with the working parts of machines or tools that ensure the creation the best conditions for cultivating crops.

The main tasks of soil cultivation are:

§ Changing the structure of the arable soil layer and its structural state to create favorable water-air and thermal regimes.

§ Strengthening the cycle of nutrients by extracting them from deeper soil horizons and influencing microbiological processes in the required direction.

§ Destruction of weeds by provoking their germination, destroying seedlings, cutting off shoots and turning rhizomes to the surface.

§ Incorporation of stubble and fertilizers.

§ Destruction of pests and pathogens of cultivated plants nesting in plant debris or in the upper layers of the soil.

§ Radical improvement of podzolic and solonetzic soils by deep cultivation.

§ Fighting water and wind erosion.

§ Preparing soil for sowing and caring for plants: leveling and compacting the soil surface or, conversely, creating a ridged surface, hilling plants, etc.

§ Destruction of perennial vegetation when cultivating virgin and fallow lands, as well as a layer of sown perennial grasses.

The roots of many wild plants can tolerate anaerobic (oxygen-free) conditions. Most cultivated plants are aerobes, and their respiration is preceded by hydrolysis (conversion of polymers into monomers) and oxygen-free oxidation of organic substances. Before sowing cultivated plants, it is necessary to plow to a depth of 22-25 cm or dig. Plowing- a method of soil cultivation that ensures wrapping and loosening of the cultivated layer of soil, as well as cutting the underground part of plants, incorporation of fertilizers and crop residues. This agrotechnical event is carried out in the fall or in early spring, before sowing, harrowing and cultivation (deep loosening) are carried out in order to improve gas exchange in the soil. After emergence and throughout the growing season, plant care consists of loosening the soil (cultivation), applying fertilizers (feeding) and watering. Loosening provides oxygen access to roots and soil microflora; fertilizers, especially organic ones, improve soil structure and soil nutrition. Watering replenishes the lack of water in plant life. Water, evaporating, prevents overheating of plants, ensures the movement of substances throughout the plant, and maintains turgor. With a lack of water, the turgor of plants drops and wilting occurs. Therefore, in the zone insufficient hydration water the plants. After watering it is necessary to carry out loosening, since water displaces oxygen from the soil. As the air temperature rises, a crust forms on the soil and strong evaporation of water occurs as a result of soil capillarity. To reduce evaporation, it is necessary to break capillarity. This can only be achieved by loosening. Loosening is called dry watering.

Root vegetables and their use by humans. As a result of a long process of evolution in connection with the performance of specialized functions, the typical taproot has been modified into a root vegetable. The root crop is formed from the main root due to the deposition of a large amount of reserve nutrients in it. The root vegetable is a thickened, juicy, fleshy main root. The root crop has three components: the head, the neck and the root itself. The root head is called top part, which bears leaves and leaf buds. From a morphological point of view, the head of the root crop is a shortened stem; a large number of leaves develop on it. The neck of the root crop is located under the head; it is smooth and bears neither leaves nor roots. The head and neck are an overgrown subcotyledon (i.e., it is also of stem origin). And only the lower part of the root crop is the root itself. Root vegetables are formed in biennial plants (beets, carrots, rutabaga, turnips, radishes, etc.). In the first year of life, nutrients accumulate; in the spring of the 2nd year, root crops are planted in the soil, and they form reproductive organs - flowers and fruits. Sugar beet roots are technical raw materials for the sugar industry, as they contain 14-20% carbohydrates. The root crops of rutabaga, turnips, radishes, carrots, and beets are essential food products and are used as medicinal plants. Fodder beet roots are used as livestock feed.

Root tubers or root cones are fleshy thickenings of lateral roots, as well as adventitious roots. Storage substances, mainly carbohydrates, starch, and inulin, can accumulate in root tubers. Root tubers are formed in orchids, chistyakov, dahlias, and earthen pears.

THE ESCAPE

The escape- an organ of higher plants, consisting of a stem with leaves and buds located on it. The main function of the shoot is photosynthesis. During development, the shoot is formed as a single organ from the seed bud, and then from the educational tissue of the growth cone. A characteristic feature of the escape is metamerism, i.e. division of its axis into similar sections - nodes with a leaf and a bud or buds and underlying internodes. Nodes and internodes, stem, leaves, buds - structural elements escape.

Rice. 17. Stem:

a, b – eastern plane tree (a – elongated, b – shortened); c – perennial shortened shoot of an apple tree (ringlet); 1 – internode; 2 – annual growth.

Bud. The bud is a rudimentary, undeveloped shoot, all parts of which are very close together. The bud consists of a rudimentary stalk surrounded by leaf primordia, and in the axils of the rudimentary leaves there are rudimentary lateral buds in the form of tubercles. The buds are covered with scales (modified leaves), which protect them from low temperatures. winter temperatures. The bud scales are often covered with hairs, a layer of cuticle, and sometimes with resinous secretions that tightly glue the bud scales and thereby protect the buds from freezing and drying out. The buds ensure long-term growth of the shoot and its branching. The top of the stalk, located in the bud, is called the growth cone. It consists of merimastic tissue, the cells of which, dividing, form a number of layers of homogeneous cells. There are lateral and apical buds. The apical buds are located at the tops of the stem and its lateral branches. Lateral buds can be axillary or adventitious. Axillary buds are located one at a time in the leaf axil. Some plants develop not one, but several buds. They can be located one above the other or next to each other. The apical and lateral axillary buds are formed from the meristem of the growth cone and differ only in location. In trees and shrubs, axillary buds are growth (vegetative) with the rudiments of leaves and stems and floral with the rudiments of flowers or inflorescences. Some axillary buds may remain dormant indefinitely. These are "dormant buds". They begin to function when the apical bud is damaged and other damage to the stem occurs.

Adventitious buds - can be located anywhere in the internode of the stem. They are formed from the cambium in the lower parts of the stems, from the surface layers of the parenchyma in the upper part of the stem.

Escape development.Stem growth in height provides the apical bud, or the bud of the seed embryo. The cells of the educational tissue of the growth cone are constantly dividing. During the division process, new primordia of leaves and buds are formed. Cell division is followed by cell growth, which entails lengthening of the internodes and the stem as a whole. In the development of a shoot, two periods are distinguished: renal - the laying of elements of the future shoot, and extra-renal - the deployment and growth of the structures of the future shoot embedded in the bud.

As one moves away from the growth cone, the ability of cells to divide decreases, and their differentiation begins with the formation of tissues. Another method of stem growth is possible: intercalary or intercalary. In this case, the educational tissue is divided by areas of non-dividing cells. It is usually located at the base of the internodes. This growth is typical for cereals.

Shoot growth in spring begins with an increase in the size of the buds and the stem and leaf primordia embedded in them. The bud scales move apart, fall off, and a young shoot appears. At the very top of the growth cone there is an apical meristem, which ensures the constant growth of the shoot in length and the formation of all its parts and tissues. The growth of the shoot ends with the formation of a flower, inflorescence or apical bud.

Stem- represents the axial part of the shoot, has unlimited growth - grows throughout the life of the plant. Functions of the stem:

1) the stem ensures the movement of water with minerals from the root upward and organic substances from the leaves to all organs;

2) the stem takes part in the formation of the crown;

3) is a place of deposition of reserve nutrients;

4) serves for vegetative propagation;

5) performs a protective function.

The components of the shoot are formed on the stem. A node is where a leaf attaches to the stem. The stem node usually has some thickening, this is especially noticeable in cereals (wheat, bamboo). The areas of the stem between two adjacent nodes are called internodes. The length of internodes varies, both in different plants and on the stem of one plant, depending on their location. For many herbaceous plants Stem internodes are present underground (dandelion, daisy). Such plants develop a large number of densely arranged leaves, which form a rosette on the soil surface (dandelion, plantain). The angle formed by the stem and the leaf extending from it is called the leaf axil.

Branching of the stem (shoot). Very few plants have a non-branching stem. In most plants, the stem branches, as a result of which the surface of the plant increases, and therefore its leaf mass. There are 4 types of branching of plant stems: dichotomous, monopodial, sympodial and false dichotomous.

Dichotomous branching- is the main primary form of plant branching, from which the others arose. It is characterized by the fact that two buds are formed at the top of the stem, which, when growing, form two identical branches in the form of a fork. Each of these branches continues to branch in the same way. This type of branching is typical for mosses, mosses, and ferns.

Rice. 18. Branching:

A – monopodial (a – diagram, b – pine branch); B – sympodial (c – diagram, d – bird cherry branch); C – false dichotomous (d – diagram, f – lilac branch);
1-4 – axes of the first and subsequent orders.

Monopodial branching characterized by unlimited apical shoot growth; characteristic of plants that have one bud at the top of the shoot. This bud serves to continue the growth of the main shoot (axis), and the lateral branches of the first order are formed due to the lateral buds, and the lateral branches do not outgrow the main shoot (conifers - spruce, pine, fir, etc.).

Sympodyl branching characterized by early cessation of apical growth, while the apical bud dies. Instead, a lateral bud develops, which moves the main axis somewhat to the side, and the shoot formed from this bud continues the main stem. Typical for trees - apple, pear, peach, etc., for herbaceous - potatoes, cotton, etc. The nature of branching determines the appearance of the plant, its habit.

At false dichotomous branching the growth of the apex on the main axis stops, and two buds are formed under it, from which more or less identical branches develop, and between them a dead apical bud (lilac, chestnut) is noticeable. It occurs when the leaves, and therefore the buds, are opposite.

Crown formation. In a branched plant, the main stem is called the axis of the first order, the axillary buds of the lateral branches developed from it are the axes of the second order, from which axes of the third order are formed, etc. Trees can have up to 20 such axes. The branched above-ground part of the tree is called the crown.

Crown formation is based on knowledge of the patterns of shoot development. Removal of the growth cone causes a cessation of stem growth in length and increased growth of lateral buds, i.e. branching. This is used by specialists when landscaping cities and forming the crown of fruit trees. The shape of the crown can be spherical (narrow maple), pyramidal (poplar), columnar (cypress), etc. The crowns of fruit and ornamental trees are formed by pruning, taking into account their natural features. Vegetable growers use this data when growing vegetables: more female flowers are formed on the side shoots of cucumbers than on the main ones. When growing flowers (roses), removing lateral flower shoots causes an increase in the size of the main shoot and the flower developing on it.

Internal structure woody stem in connection with its functions. Stem growth in thickness. Formation of tree rings. A characteristic feature of a woody stem is the ability to grow in thickness indefinitely, giving growth each growing season. Anatomical features consist in the formation of periderm (secondary integumentary tissue) on its surface, which replaces the epidermis, and the appearance of clearly defined growth rings in the wood. A woody stem is usually divided into bark, cambium, wood and pith.

The cortex includes all tissues located to the surface from the cambium. The outer layers of the cortex are represented by the periderm, consisting of cork, cork cambium and phelloderm. Sometimes remnants of the epidermis remain on the surface of the cork. Behind the periderm are elements of the primary cortex, resulting from the differentiation of the primary educational tissue of the growth cone. It includes lamellar collenchyma, cells of the main tissue, endoderm, which contains starch grains. Behind the endodermis is pericyclic sclerenchyma - these are lignified sclerenchyma fibers. Behind the pericyclic sclerenchyma, the phloem or secondary cortex begins. It consists of soft bast and hard bast. The soft bast is represented by sieve tubes with companion cells and phloem parenchyma, and the hard bast is represented by secondary sclerenchyma fibers. They arise as a result of the activity and differentiation of cambium cells. The cambium alternately deposits elements of soft and then elements of hard bast. Hard bast fibers are dead cells with highly thickened lignified walls - bast fibers. The phloem zone includes the primary medullary rays, which expand into triangles from the cambium. They are represented by cells of the main parenchyma and are the site of deposition of reserve nutrients. Continuing in the form of narrow stripes along the xylem, the primary medullary rays reach the core of the stem. There are also secondary medullary rays, which end in the xylem before reaching the pith; they are significantly narrower than the primary rays. They also arise from cambium cells. The part of the stem from the cambium to the endodermis is called the secondary cortex. Together with the primary bark, it forms the bark part of the stem.

The cambium consists of dividing rectangular thin-walled cells with living contents. When it functions vigorously, its cells do not have time to differentiate, and the cambium, together with the cells formed from it, is clearly distinguishable.

Rice. 19. The structure of a dicotyledonous trunk woody plant:

1 - remnants of the epidermis; 2 – periderm; 3 – collenchyma; 4 – parenchyma of the primary cortex; 5 – sclerenchyma of pericyclic origin; 6 – phloem part of the primary medullary ray; 7 – bast fibers; 8 – soft bast; 9 – cambium; 10 – spring wood; 11 – autumn wood; 12 – xylem part of the primary medullary ray; 13 – primary xylem; 14 – core parenchyma; A – cortex (a΄ - primary; a΄΄ - secondary); B – wood; (I-III – annual wood growth); B – core.

The bulk of the stem of a woody plant consists of secondary wood (constituting 9/10 of the volume of the trunk), which goes from the cambium to the center. Wood (xylem) includes tracheae (vessels), tracheids, wood parenchyma, and wood fibers (sclerenchyma). A common feature of all xylem elements is lignification of the cell walls. Due to the uneven activity of the cambium, the wood cells formed by it have different sizes. The largest cells are formed in the spring, when cambium activity is most intense. Gradually, the activity of the cambium slows down, and the cells formed by the cambium become smaller and thicker-walled. By winter, the cambium enters a dormant period. Thus, during one growing season one tree ring, in which spring, summer and autumn cells are clearly visible. After a period of winter dormancy, cambium activity resumes and the new growth ring, the large spring cells of which are directly adjacent to the small cells formed in the fall of the previous year. As a rule, within a year it is formed only one ring of wood. By the width of the growth rings you can find out in what conditions the tree grew in different years life. Narrow growth rings indicate a lack of moisture, shading of the tree, and poor nutrition. The cardinal directions can also be determined by the growth rings. Tree rings are usually wider on the side of the tree that faces south and narrower on the side that faces north. Following the secondary wood towards the center are the primary wood elements, which consist of a small number of spiral and ringed vessels.

In the center of the stem there is a core consisting of round parenchyma cells. Various substances accumulate in them. The growth of the stem in thickness occurs due to the cells of the secondary educational tissue of the cambium. About four times more cells are deposited toward the wood than toward the bark, which is why the wood is thicker than the bark.

Movement of mineral and organic substances along the stem occurs in two directions. An ascending current flows from the root to the leaves and all above-ground organs through the conducting vessels of wood (xylem) (water and mineral salts). The rise of water to the height of the stem (and it can reach about a hundred meters) is facilitated by the suction action of leaves, root pressure, and the force of adhesion of water molecules to each other and to the walls of blood vessels. Due to the sucking force of the leaves, negative hydrostatic pressure is created in the stem. This is evidenced by observations: when cutting a tree, air is sucked into the wood with a hiss. Due to the cohesive force between water molecules in the conducting system, a continuous column of liquid is formed, pulled up from above by the suction force of the leaves and pushed from below by root pressure (upward current).

Movement of organic substances occurs through the sieve tubes of the bast (phloem) from the leaves to the root (downward flow). This is not a simple mechanical phenomenon, but a physiological process that involves the expenditure of energy, i.e. associated with breathing. In summer, organic matter enters not only the roots, but also the flowers and fruits, which are often located above the leaves. Consequently, organic matter moves both down and up. In addition to the movement of nutrients vertically, in plants they move horizontally from the core of the trunk to the periphery. For this purpose, medullary rays are used, which consist of the main tissue and stretch from the core through the wood to the bark. They are called rays because of their shape: they begin as narrow stripes in the core, widen slightly in the wood and very strongly in the bark.

Deposition of reserve substances. Reserve or organic nutrients are deposited in special storage tissues of the pith, medullary rays and in the cells of the main tissue of the primary cortex in the form of sugar, starch, amino acids, proteins, and oils. They can accumulate in dissolved (beet roots), solid (starch grains, protein in potato tubers, cereal fruits, legumes) or semi-liquid states (oil droplets in the endosperm of castor beans). Especially a lot of substances are deposited in modified shoots (rhizomes, tubers, bulbs), as well as in seeds and fruits. The importance of reserve substances lies not only in the fact that the plant, if necessary, feeds on these organic substances, but also in the fact that they are a food product for humans and animals, and are also used as raw materials.

Modified shoots: rhizome, tuber, bulb, their structure, biological and economic significance.

In connection with the performance of additional functions, the stem undergoes various modifications, both aboveground (tendrils, spines) and underground - rhizomes, tubers, bulbs, which perform the functions of accumulating reserve nutrients and vegetative propagation.

Rhizome- a perennial underground shoot with scales and buds. It differs from the root in the absence of a root cap, the presence of nodes and internodes, leaves (and after they die, leaf scars), and the presence of apical and axillary buds. The shape can be long and thin (long-rhizome plants - wheatgrass) or short and thick (short-rhizoma plants - sorrel, iris). Every year an underground shoot grows from the top. If the rhizome is damaged, each piece with a bud gives rise to a new plant, which is located parallel to the soil.

Rice. 20. Metamorphoses of underground shoots.

Basic plant root functions the following:

• serves as the main organ for the absorption of mineral elements from the soil;
• primarily synthesizes some organic substances containing nitrogen, phosphorus and sulfur;
• often serves as a reservoir for reserve nutrients;
• anchors the plant in the soil.

Functions of plant roots in scientific research

• Even I.V. Michurin established that roots have a very significant influence on a number of physiological characteristics of grafted plants. The roots of the wild rootstock (more details:) usually worsened the quality of the fruit, while the roots of the cultivated variety improved it.
• L. S. Litvinov and N. G. Potapov showed that the transformation of some mineral substances (more details:) coming from the soil into complex organic compounds occurs in root tissues.
• According to N.G. Potapov, in corn, from 50 to 70% of absorbed nitrogen enters the above-ground part in the form of organic compounds, of which up to 30% are amino acids.
• A.L. Kursanov, using C 14 and N 15, (more details:) established that carbon dioxide absorbed by the roots is part of organic acids. The conversion of phosphorus and sulfur also partially occurs in the roots.
• I.I. Kolosov, working with P 32, clarified the issue of the transformation of phosphorus in the roots: it entered the above-ground organs in the form of nucleoproteins and lipoids.
• A. A. Shmuk and G. S. Ilyina showed that the formation of nicotine occurs in the roots of the plant: when tobacco was grafted onto the roots of tomato and nightshade, there was no nicotine in the leaves.

All these data indicate the possibility of synthesizing a wide variety of organic compounds in roots.

Root structure

Morphological-anatomical root structure well adapted to absorb water and mineral elements from the soil. However, not the entire root participates in the absorption of mineral elements and water, but only its absorption zone - the part of the root bearing root hairs.
Diagram of the growing root zone. 1 - zone of root hairs, 2 - zone of elongation, 3 - zone of intensive cell division, 4 - root cap. Root hairs increase the suction surface of the root many times over, and as a result, the contact surface between the root and the soil increases. Root hairs are very short-lived and die off after 10-20 days. New root hairs are constantly being formed on the growing root zone.

The roots of the vast majority of plants perform six main functions:

Roots hold the plant in a certain position. This function is obvious for terrestrial plants; it is especially significant for large trees with a large mass of branches and leaves. For many aquatic plants fastening to the bottom allows you to advantageously distribute the leaves in space. In floating plants, such as duckweed, the roots prevent the plant from turning over.

The roots provide soil nutrition to the plant, absorbing water from the soil with minerals dissolved in it, and conducting substances to the shoot (Fig. 1).

In some plants, reserve nutrients such as starch and other carbohydrates are stored in the main root.

The formation of certain substances occurs in the roots, needed by the body plants. Thus, in the roots, nitrates are reduced to nitrites, and some amino acids and alkaloids are synthesized.

Roots can carry out symbiosis with fungi and microorganisms living in the soil (mycorrhiza, nodules of representatives of the legume family).

With the help of roots, vegetative propagation can be carried out (for example, by root suckers). Plants such as dandelion, plum, raspberry, and lilac reproduce by root suckers.

Absorption of water and minerals by the root

This function arose in plants in connection with their access to land.

The absorption of water and minerals by the plant occurs independently of each other, since these processes are based on different mechanisms of action. Water passes into the root cells passively, and minerals enter the root cells mainly as a result of active transport, which involves energy expenditure.

Rice. 1. Horizontal water transport:

1 - root hair; 2 - apoplastic pathway; 3 - symplastic path; 4 - epiblema (rhizoderm); 5 - endoderm; 6 - pericycle; 7 - xylem vessels; 8 - primary cortex; 9 - plasmodesmata; 10 - Casparian belts.

Water enters the plant mainly according to the law of osmosis. Root hairs have a huge vacuole with concentrated cell sap, which has a high osmotic potential, which ensures the flow of water from the soil solution into the root hair.

Horizontal transport of substances

Water enters the plant body through rhizoderm, the surface of which is greatly enlarged due to the presence of root hairs.

In this zone, in the conducting cylinder of the root, the root conducting system is formed - xylem vessels, which is necessary to ensure the upward flow of water and minerals.

Water with mineral salts is absorbed by root hairs. The endoderm pumps these substances into the conducting cylinder, creating root pressure and preventing water from escaping. Water with salts enters the vessels of the conducting cylinder and rises through the transpiration current along the stem to the leaves.

VERTICAL TRANSPORT OF SUBSTANCES

Roots carry water and minerals to the ground organs of the plant.

Vertical movement of water occurs through dead xylem cells that are unable to push water to the leaves. This movement is supported by the transpiration function of the leaves.

Definition

Root pressure- the force with which the root pumps water into the stem.

The root actively pumps mineral and organic substances into xylem vessels; as a result, increased osmotic pressure occurs in the root vessels relative to the pressure of the soil solution. The root pressure can reach 3 atm. Evidence of the presence of root pressure is, for example, guttation(release of water droplets from leaves).

OSMOSIS AND TURGOR

The flow of water from the soil into the root and its movement along the stem is determined by the difference in osmotic pressure.

The pressure of the cell sap solution exerted on the cytoplasm and cell walls is called osmotic.

Since the concentration of organic and mineral substances inside the root hair is higher than in the soil, environment in relation to the cell sap of root hairs it is a hypotonic solution. By absorbing water, the hair cell dilutes the concentration of cell sap. Gradually, the cell sap of the hairs becomes hypotonic in relation to the deeper located cells of the cortex. And water, entering them from root hairs, also reduces the concentration of substances in the juice. Now, in the next groups of cells, the concentration of juice will be higher than in the previous ones. As water is absorbed, the concentration of sap from the cortex cells to the xylem vessels will increase. However, due to the fact that water leaves the root hair, the concentration of organic matter in it increases again, which ensures further absorption of water from the soil. The outer membrane of the cells of the root skin and root hair is a semi-permeable membrane, permeable to the soil solution and almost impermeable to substances dissolved in the cell sap.

The one-way passage of solutions through semi-permeable membranes that separate solutions of different concentrations is called osmosis.

Osmotic pressure is opposed by the pressure of a stretched cell wall - turgorous. The intensity of water absorption by the outer root cells depends on the suction force with which water penetrates into the cell vacuole.

Definition

Sucking force is the difference between osmotic and turgor pressures.

The suction force of all the root hairs of the root creates root pressure, due to which water enters the vessels and rises. The force with which water flows from the root to the stem is called root pressure.

Thus, the movement of water and salts dissolved in it is facilitated by the suction force of root hairs, root pressure, the adhesion force between water molecules and the walls of blood vessels, as well as the suction force of leaves, which, constantly evaporating water, attract it from the roots.

Expand

In the living cells of the root, the first selection of substances allowed into the plant occurs. The participation of living cells in the intake of substances determines the selective ability of the plant, due to which different substances are absorbed in different quantities. Since intake is highly dependent on consumption, the plant takes in some salts and then others at different stages of development. The more developed the root system, the more active the absorption of water and salts.

Situations often arise when plant roots perform some additional functions or one of the main functions requires more development. In such cases, modifications of the roots are formed (see Modifications of plant organs).