Calcium, magnesium and sulfur in plant organisms. What is calcium, the reaction of calcium with oxygen Calcium plus sulfur why is it a heterogeneous reaction

In relation to calcium, plants are divided into three groups: calciumphiles, calciumphobes and neutral species. The calcium content in plants is 0.5 - 1.5% of the dry matter weight, but in mature tissues of calciophilic plants it can reach 10%. The above-ground parts accumulate more calcium per unit mass than the roots.

The chemical properties of calcium are such that it easily forms fairly strong and at the same time labile complexes with oxygen compounds of macromolecules. Calcium can bind intramolecular sites of proteins, leading to changes in conformation, and form bridges between complex compounds of lipids and proteins in the membrane or pectin compounds in the cell wall, ensuring the stability of these structures. Therefore, accordingly, with calcium deficiency, membrane fluidity sharply increases, the processes of membrane transport and bioelectrogenesis are also disrupted, cell division and elongation are inhibited, and root formation processes stop. Lack of calcium leads to swelling of pectin substances and disruption of the structure of cell walls. Necrosis appears on the fruits. At the same time, the leaf blades become bent and twisted, the tips and edges of the leaves initially turn white and then turn black. Roots, leaves and individual sections of the stem rot and die. The lack of calcium primarily affects young meristematic tissues and the root system.

Ca 2+ ions play an important role in regulating the uptake of ions by plant cells. The excess content of many cations toxic to the plant (aluminum, manganese, iron, etc.) can be neutralized by binding to the cell wall and displacing Ca 2+ ions from it into the solution.

Calcium has important in cellular signaling processes as a secondary messenger. Ca 2+ ions have the universal ability to conduct a wide variety of signals that have a primary effect on the cell - hormones, pathogens, light, gravitational and stress influences. The peculiarity of the transmission of information in the cell using Ca 2+ ions is the wave method of signal transmission. Ca waves and Ca oscillations, initiated in certain areas of cells, are the basis of calcium signaling in plant organisms.

The cytoskeleton is very sensitive to changes in the content of cytosolic calcium. Local changes in the concentration of Ca 2+ ions in the cytoplasm play an extremely important role in the processes of assembly (and disassembly) of actin and intermediate filaments, and in the organization of cortical microtubules. Calcium-dependent functioning of the cytoskeleton takes place in processes such as cyclosis, flagellar movement, cell division, and polar cell growth.

Sulfur is one of the essential nutrients necessary for plant life. Its content in plant tissues is relatively small and amounts to 0.2 - 1.0% based on dry weight. Sulfur enters plants only in oxidized form - in the form of sulfate ion. Sulfur is found in plants in two forms - oxidized and reduced. The main part of the sulfate absorbed by the roots moves to the above-ground part of the plant through xylem vessels to young tissues, where it is intensively included in the metabolism. Once in the cytoplasm, sulfate is reduced to form sulfhydryl groups of organic compounds (R-SH). From leaves, sulfate and reduced forms of sulfur can move both acropetally and basipetally into the growing parts of the plant and into storage organs. In seeds, sulfur is found primarily in organic form. The proportion of sulfate is minimal in young leaves and increases sharply as they age due to protein degradation. Sulfur, like calcium, is not capable of reutilization and therefore accumulates in old plant tissues.

Sulfhydryl groups are part of amino acids, lipids, coenzyme A and some other compounds. The need for sulfur is especially high in plants rich in proteins, such as legumes and members of the cruciferous family, which large quantities synthesize sulfur-containing mustard oils. It is part of the amino acids cysteine ​​and methionine, which can be found both in free form and as part of proteins.

One of the main functions of sulfur is associated with the formation of the tertiary structure of proteins due to covalent bonds of disulfide bridges formed between cysteine ​​residues. It is part of a number of vitamins (lipoic acid, biotin, thiamine). Another one important function sulfur is to maintain a certain value of the redox potential of the cell through reversible transformations:

Insufficient supply of plants with sulfur inhibits protein synthesis, reduces the intensity of photosynthesis and the rate of growth processes. External symptoms of sulfur deficiency are pale and yellowed leaves, which manifests itself first in the youngest shoots.

Magnesium ranks fourth in terms of content in plants after potassium, nitrogen and calcium. In higher plants, its average content per dry weight is 0.02 - 3.1%, in algae 3.0 - 3.5%. There is especially a lot of it in young cells, generative organs and storage tissues. The accumulation of magnesium in growing tissues is facilitated by its relatively high mobility in the plant, which makes it possible to recycle this cation from aging organs. However, the degree of reutilization of magnesium is much lower than that of nitrogen, phosphorus and potassium, since part of it forms oxalates and pectates that are insoluble and cannot move throughout the plant.

Most of the magnesium in seeds is found in phytin. About 10-15% Mg is part of chlorophyll. This function of magnesium is unique, and no other element can replace it in the chlorophyll molecule. The participation of magnesium in the metabolism of plant cells is associated with its ability to regulate the work of a number of enzymes. Magnesium is a cofactor for almost everyone. enzymes that catalyze the transfer of phosphate groups are necessary for the operation of many of the enzymes of glycolysis and the Krebs cycle, as well as alcoholic and lactic acid fermentation. Magnesium in a concentration of at least 0.5 mM is required for the formation of ribosomes and polysomes, activation of amino acids and protein synthesis. With an increase in the concentration of magnesium in plant cells, enzymes involved in the metabolism of phosphate are activated, which leads to an increase in the content of organic and inorganic forms of phosphorus compounds in the tissues.

Plants experience magnesium starvation mainly on sandy and podzolic soils. Its deficiency primarily affects phosphorus metabolism and, accordingly, the energy of the plant, even if phosphates are present in sufficient quantities in the nutrient substrate. Magnesium deficiency also inhibits the conversion of monosaccharides into polysaccharides and causes serious disturbances in the processes of protein synthesis. Magnesium starvation leads to disruption of the plastid structure - the grana stick together, the stromal lamellae are torn and do not form a single structure, instead many vesicles appear.

An external symptom of magnesium deficiency is interveinal chlorosis, associated with the appearance of spots and stripes of light green, and then yellow color between the green veins of the leaf. The edges of the leaf blades will turn yellow, orange, red or dark red. Signs of magnesium starvation first appear on old leaves, and then spread to young leaves and plant organs, with leaf areas adjacent to the vessels remaining green longer.

DEFINITION

Calcium sulfide– a medium salt formed by a strong base – calcium hydroxide (Ca(OH) 2) and a weak acid – hydrogen sulfide (H 2 S). Formula - CaS.

Molar mass – 72 g/mol. Is a powder white, which absorbs moisture well.

Hydrolysis of calcium sulfide

Hydrolyzes at the anion. The nature of the environment is alkaline. Theoretically, a second stage is possible. The hydrolysis equation is as follows:

First stage:

CaS ↔ Ca 2+ + S 2- (salt dissociation);

S 2- + HOH ↔ HS - + OH - (hydrolysis at the anion);

Ca 2+ + S 2- + HOH ↔ HS - + Ca 2+ + OH - (equation in ionic form);

2CaS + 2H 2 O ↔ Ca(HS) 2 + Ca(OH) 2 ↓ (equation in molecular form).

Second stage:

Ca(HS) 2 ↔ Ca 2+ +2HS - (salt dissociation);

HS - + HOH ↔H 2 S + OH - (hydrolysis at the anion);

Ca 2+ + 2HS - + HOH ↔ H 2 S + Ca 2+ + OH - (equation in ionic form);

Ca(HS) 2 + 2H 2 O ↔ 2H 2 S + Ca(OH) 2 ↓ (equation in molecular form).

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

In ancient times, people used calcium compounds for construction. Basically it was calcium carbonate found in rocks, or a product of its firing - lime. Marble and plaster were also used. Previously, scientists believed that lime, which is calcium oxide, was a simple substance. This misconception existed until the end of the 18th century, until Antoine Lavoisier expressed his assumptions about this substance.

At the beginning of the 19th century, the English scientist Humphrey Davy discovered calcium in its pure form using electrolysis. Moreover, he received a calcium amalgam from slaked lime and mercury oxide. Then, having distilled off the mercury, he obtained metallic calcium.

The reaction of calcium with water occurs violently, but is not accompanied by fire. Due to the abundant release of hydrogen, the calcium plate will move through the water. A substance is also formed - calcium hydroxide. If phenolphthalein is added to a liquid, it will turn a bright crimson color - therefore, Ca(OH)₂ is a base.

Ca + 2H₂O → Ca(OH)₂↓ + H₂

Reaction of calcium with oxygen

The reaction of Ca and O₂ is very interesting, but the experiment cannot be performed at home, as it is very dangerous.

Let's consider the reaction of calcium with oxygen, namely the combustion of this substance in air.

Attention! Do not try to repeat this experience yourself! you'll find safe chemistry experiments you can do at home.

Let's take potassium nitrate KNO₃ as a source of oxygen. If calcium was stored in kerosene liquid, then before the experiment it must be cleaned using a burner, holding it over the flame. Next, the calcium is dipped into KNO₃ powder. Then the calcium with potassium nitrate must be placed in the flame of the burner. The decomposition reaction of potassium nitrate into potassium nitrite and oxygen occurs. The released oxygen ignites the calcium, and the flame turns red.

KNO₃ → KNO₂ + O₂

2Ca + O₂ → 2CaO

It is worth noting that calcium reacts with some elements only when heated, these include: sulfur, boron, nitrogen and others.

As yields increase, the importance of providing fields with sufficient quantities of each of the 17 essential nutrients increases. In particular, due to a number of factors, the need for calcium, magnesium and sulfur has increased. In this regard, we present recommendations from American consultants on the addition of mesoelements.

Application of fertilizers that do not contain mesoelements. Typically, fertilization is carried out with fertilizers that do not contain magnesium or sulfur: diammonium phosphate, urea, ammonium nitrate, nitrogen, phosphorus or potassium chloride. Because of this, a deficiency of sulfur or magnesium occurs. These fertilizers, as well as monoammonium phosphate and anhydrous ammonia, do not contain any calcium, magnesium, or sulfur. Among all common fertilizers, only triple superphosphate contains 14% calcium and contains no magnesium or sulfur at all.

Yield growth. Over the past decade, yields have increased significantly. Corn, which yields 12.5 t/ha, uses 70 kg/ha of magnesium and 37 kg/ha of sulfur. For comparison: with a yield of 7.5 t/ha, magnesium is removed 33 kg/ha, and sulfur – 22 kg/ha.

Reducing the use of sulfur-containing pesticides. Previously, farmers could rely on insecticides and fungicides for sulfur sources. Now many of these pesticides have been replaced by products that do not contain sulfur.

Limiting emissions into the atmosphere. The United States limits emissions from metallurgical furnaces and power plants. Many other countries have reduced sulfur emissions from gas combustion in domestic and industrial boilers. In addition, in modern cars, catalytic converters absorb sulfur, which was previously released into the atmosphere along with exhaust. All these factors reduced the return of sulfur to the soil along with rain.

Removal of mesoelements with the harvest, kg/ha

Calcium

Insufficient attention is paid to calcium when drawing up fertilization schemes for many high-yielding and fruit crops. The exception is tomatoes and peanuts, which require good calcium nutrition when growing.

In soil, calcium replaces hydrogen ions on the surface of soil particles when lime is added to reduce acidity. It is essential for microorganisms that convert crop residues into organic matter, release nutrients, and improve soil structure and water-holding capacity. Calcium helps nitrogen-fixing nodule bacteria to work.

Functions of calcium in a plant:

calcium, along with magnesium and potassium, helps neutralize organic acids formed as a result of cellular metabolism in plants;

improves the absorption of other nutrients by the roots and their transport by the plant;

activates a number of enzyme systems that regulate plant growth;

helps convert nitrate nitrogen into forms necessary for the formation of proteins;

necessary for the formation of cell walls and normal cell division;

improves disease resistance.

Calcium deficiency

Calcium deficiency most often occurs in acidic, sandy soils due to leaching by rain or irrigation water. It is not typical for soils where sufficient lime has been added to optimize pH levels. As soil acidity increases, plant growth becomes more difficult due to increasing concentrations of toxic elements - aluminum and/or manganese, but not due to a lack of calcium. Soil testing and adequate liming is the best way to avoid such problems.

Calcium deficiency can be avoided by regularly testing the soil and adjusting the acidity by applying optimal doses of lime. It is necessary to adhere to a balanced application of calcium, magnesium and potassium. There is antagonism between these elements: an overdose of one leads to a deficiency or neutralization of the other. In addition, calcium must be added not just like that, but at certain phases in order to ensure certain functions of the plant.

Sources of calcium

Good liming effectively provides calcium to most crops. High quality calcitic lime is effective when pH adjustment is required. When magnesium deficiency is also observed, dolomitic limestones or calcitic limestones can be added along with a magnesium source such as potassium-magnesium sulfate. Gypsum (calcium sulfate) is a source of calcium at the appropriate pH level.

Main sources of calcium

Magnesium

Plants need energy to grow. Wheat and other crops need magnesium to support photosynthesis. Magnesium is an essential component of chlorophyll molecules: each molecule contains 6.7% magnesium.

Magnesium also acts as a transporter of phosphorus in the plant. This is necessary for cell division and protein formation. The absorption of phosphorus is impossible without magnesium, and vice versa. Thus, magnesium is necessary for phosphate metabolism, plant respiration and the activation of a number of enzyme systems.

Magnesium in soil

The Earth's crust contains 1.9% magnesium, mainly in the form of magnesium-containing minerals. With the gradual weathering of these minerals, some of the magnesium becomes available to plants. The reserves of available magnesium in the soil are in some places depleted or depleted due to leaching, absorption by plants and chemical metabolic reactions.

The availability of magnesium to plants is often dependent on soil pH. Research has shown that the availability of magnesium to plants is reduced at low pH values. In acidic soils with a pH less than 5.8, excess hydrogen and aluminum affect the availability of magnesium and its uptake by plants. At high pH (above 7.4), excess calcium can interfere with magnesium uptake by plants.

Sandy soils with low cation exchange capacity have a low ability to supply plants with magnesium. Application of lime with a high calcium content can exacerbate magnesium deficiency by activating plant growth and increasing the need for magnesium. High application rates of ammonium and potassium can upset the nutritional balance due to the effect of ion competition. The limit below which the content of exchangeable magnesium is considered low and the application of magnesium is justified is 25-50 parts per million or 55-110 kg/ha.

For soils with a cation exchange capacity greater than 5 mEq per 100 g, the soil calcium to magnesium ratio should be maintained at approximately 10:1. For sandy soils with a cation exchange capacity of 5 mEq or less, the calcium to magnesium ratio should be maintained at approximately level 5:1.

How to compensate for magnesium deficiency

If leaf analysis reveals a magnesium deficiency in a growing plant, it can be compensated by the supply of magnesium in soluble form along with rain or irrigation water. This makes magnesium available to the root system and absorption by plants. Small doses of magnesium can also be applied through the leaf to correct the content of this element or prevent its deficiency. But it is better to add magnesium to the soil before sowing or before the active growth of the crop begins.

Sources of magnesium

Sulfur

Sulfur in the soil

The source of sulfur for plants in the soil is organic matter and minerals, but often they are not enough or they are in a form inaccessible to high-yielding crops. Most sulfur in soil is bound in organic matter and is not available to plants until it is converted to the sulfate form by soil bacteria. This process is called mineralization.

Sulfates are as mobile in the soil as nitrogen in the nitrate form, and in some soil types can be washed out of the root zone by intense rainfall or irrigation. Sulfates can move back to the soil surface with the evaporation of water, with the exception of sandy soils or soils of coarse texture where the capillary pores are broken. The mobility of sulfate sulfur makes it difficult to measure its content in soil tests and to use such tests to predict sulfur application requirements.

Sulfur is contained to a greater extent in clay soil particles than nitrate nitrogen. Intense rains in early spring can wash sulfur from the top layer of soil and bind it in the bottom layer if the top layer is sandy and the bottom layer is clayey. Therefore, crops growing in such soils may show symptoms of sulfur deficiency early in the growing season, but as roots penetrate into the lower layers of the soil, this deficiency may resolve. On soils that are sandy throughout the entire profile, with little or no clay layer, crops will respond well to the addition of sulfur.

Sulfur in plants

Sulfur is part of every living cell and is necessary for the synthesis of certain amino acids (cysteine ​​and methionine) and proteins. Sulfur is also important for photosynthesis and winter hardiness of crops. In addition, sulfur is important for the process of converting nitrate nitrogen into amino acids.

Sulfur deficiency

When visually analyzed, sulfur deficiency is often confused with nitrogen deficiency. In both cases, there is a lag in plant growth, accompanied by a general yellowing of the leaves. Sulfur in the plant is immobile and does not move from old to young leaves. With sulfur deficiency, young leaves often turn yellow first, while with nitrogen deficiency, old leaves turn yellow. If the deficiency is not very severe, its symptoms may not be visually apparent.

The most reliable way to diagnose sulfur deficiency is to test plant samples for both sulfur and nitrogen levels. The normal sulfur content in plant tissues of most crops ranges from 0.2 to 0.5%. The optimal level of the ratio between nitrogen and sulfur is from 7: 1 to 15: 1. If the ratio goes beyond the above limits, this may signal a sulfur deficiency, but for an accurate diagnosis this indicator should be considered in conjunction with the absolute indicators of nitrogen and sulfur content.

Under conditions of sulfur deficiency, nitrogen can accumulate in nitrate form. Accumulation of nitrates in the plant can prevent seed formation in some crops such as canola. Therefore, balancing sulfur content with nitrogen content is important for plant health.

Crops such as alfalfa or corn, which produce high dry matter yields, require maximum sulfur doses. Also, potatoes and many vegetable crops need sulfur in large quantities and bear fruit better when fertilizers containing sulfur are applied. Without a balanced sulfur diet, crops that receive high doses of nitrogen fertilizer may suffer from sulfur deficiency.

Sources of sulfur

Sometimes irrigation water can contain significant amounts of sulfur. For example, when the sulfate sulfur content in irrigation water exceeds 5 parts per million, there are no prerequisites for sulfur deficiency. Most sulfur-containing fertilizers are sulfates, which have a moderate to high degree of water solubility. The most important source of water-insoluble sulfur is elemental sulfur, which can be oxidized to sulfates by microorganisms before being used by plants. Oxidation occurs when the soil is warm, has adequate moisture, aeration and sulfur particle size. Elemental sulfur is well absorbed by the soil and then by crops.

Sources of sulfur

Macroelements are elements that can be included in a plant in whole percentages or tenths of a percent. These include phosphorus, nitrogen, cations - potassium, sulfur, calcium, magnesium, while iron is an intermediate element between micro and macroelements.

The element is perfectly absorbed by the plant from ammonium and nitric acid salts. It is the main nutritional element for roots, because it is part of the proteins in living cells. The protein molecule has a complex structure, protoplasm is built from it, the nitrogen content ranges from 16% to 18%. Protoplasm is a living substance in which the main physiological process occurs, namely respiratory exchange. Only thanks to protoplasm does the complex synthesis of organic substances occur. Nitrogen is also a component of nucleic acid, which is part of the nucleus and is also a carrier of heredity. The great importance of the element is determined by the fact that this macroelement is part of chlorophyll green; the process of photosynthesis depends on this pigment; it is also part of some enzymes that regulate metabolic reactions and a number of different vitamins. Small amounts of nitrogen can be found in inorganic environments. With a lack of light or excess nitrogen nutrition, nitrates can accumulate in the cell sap.

Most forms of nitrogen are converted in the plant into ammonia compounds, which, when reacting with organic acids, form amides-asparagine, amino acids and glutamine. Ammonia nitrogen most often does not accumulate in large quantities in the plant. This can only be observed when there is an insufficient amount of carbohydrates; under such conditions, the plant is not able to process it into harmless substances - glutamine and asparagine. Excessive ammonia in tissues can cause direct tissue damage. This circumstance should be taken into account when growing plants in winter in a greenhouse. A high proportion of ammonia nitrogen in the nutrient substrate and insufficient illumination can reduce the process of photosynthesis and can also lead to damage to the leaf parenchyma due to the high ammonia content.

Vegetable plants need nitrogen throughout the growing season as they are always building new parts. With a lack of nitrogen, the plant begins to grow poorly. New shoots do not form, the size of the leaves decreases. If nitrogen is missing from old leaves, the chlorophyll in them is destroyed, causing the leaves to turn pale green, then turn yellow and die. During acute starvation, the middle tiers of leaves become yellow, and the upper ones become pale green. This phenomenon can be dealt with easily. To do this, you only need to add nitrate salt to the nutrient, so that after 5 or 6 days the leaves become dark green in color and the plant continues to create new shoots.

This element can be absorbed by the plant only in its oxidized form – the SO4 anion. In this plant, a large mass of the sulfate anion is reduced to -S-S- and –SH groups. In such groups, sulfur is part of proteins and amino acids. The element is part of some enzymes, also enzymes involved in the respiratory process. Consequently, sulfur compounds strongly influence metabolic processes and energy production.

Sulfur is also present in cell sap as a sulfate ion. When sulfur-containing compounds decompose, with the participation of oxygen, sulfur is oxidized to sulfate. If the root dies due to lack of oxygen, then compounds containing sulfur break down into hydrogen sulfide, which is poisonous to living roots. This is one of the reasons for the death of the entire root system due to lack of oxygen and its flooding. If there is a deficiency of sulfur, then, just like with nitrogen, chlorophyll is resolved, but the leaves of the upper layers are the first to experience a deficiency of sulfur.

This element is absorbed only in oxidized form with the help of salts of phosphoric acids. The element is also found in (complex) proteins - nucleoproteins; they are the most important substances in the plasma and nucleus. Phosphorus is also part of fat-like substances and phosphatides, which play a critical role in the formation of membrane surfaces in cells and are part of some enzymes and other active compounds. The element plays an important role in aerobic respiration and glycolysis. The energy that is released during these processes accumulates in the form of phosphate bonds, and is subsequently used for the synthesis of many substances.

Phosphorus also takes part in the process of photosynthesis. In a plant, phosphoric acid cannot be reduced; it can only bind with other organic substances, forming phosphorus esters. Phosphorus is found in large quantities in the natural environment, and it accumulates in cell sap with the help of mineral salts, which are a reserve fund of phosphorus. The buffering properties of phosphoric acid salts are able to regulate acidity in the cell, maintaining a favorable level. The element is very necessary for plant growth. If at first the plant lacks phosphorus, and then after feeding with phosphorus salts, the plant may suffer from an increased supply of this element and a disturbance in nitrogen metabolism due to this. Therefore, it is very important to provide good conditions for phosphorus nutrition throughout the entire life cycle of the plant.

Calcium, magnesium and potassium are absorbed by the plant from various salts (soluble), the anions of which do not have a toxic effect. They are accessible when they are in absorbed form, namely, associated with some insoluble substance that has acidic properties. When they enter a plant, calcium and potassium do not undergo chemical transformations, but they are necessary for nutrition. And they cannot be replaced by other elements, just as sulfur, nitrogen or phosphorus cannot be replaced.

The main role of magnesium, calcium and potassium is that when they are adsorbed on colloidal particles of protoplasm, they form special electrostatic forces around them. These forces play an important role in the formation of the structure of living matter, without which neither the synthesis of cellular substances nor the joint activity of various enzymes can occur. At the same time, the ions hold a certain number of water molecules around them, which is why the total volume of the ions is not the same. The forces that hold the ion directly on the surface of the colloidal particle are also not equal. It is worth noting that the calcium ion has the smallest volume - it is able to adhere to the colloidal surface with greater force. The potassium ion has the largest volume, which is why it is able to form less strong adsorption bonds, and the calcium ion can displace it. The magnesium ion occupied an intermediate position. Since during adsorption, ions try to retain the water shell, they determine the water-holding force and water content of colloids. If there is potassium, then the water-holding power of the tissue increases, and with calcium it decreases. From the above it follows that in the creation of internal structures, the important thing is the ratio of various cations, and not their absolute content.

In plants, the element is contained in greater quantities than other cations, especially in vegetative parts. Most often found in cell sap. There is also a lot of it in young cells, which are rich in protoplasm, a significant amount of potassium in the adsorbed state. The element is able to influence plasma colloids; it liquefies protoplasm (increases its hydrophilicity). Potassium is also a catalyst for many synthetic processes: it usually catalyzes the synthesis of simple high-molecular substances, promoting the formation of starch, proteins, sucrose and fats. If observed, a lack of potassium may disrupt synthesizing processes, and amino acids, glucose and other breakdown products will begin to accumulate in the plant. If there is a lack of potassium, a marginal fuse forms on the leaves of the lower layer - this is when the edges of the leaf blade die off, after which the leaves acquire a dome-shaped shape and brown spots form on them. Necrosis or brown spots are associated with the formation of cadaveric poison in plant tissues and a violation of nitrogen metabolism.

The element must be supplied to the plant during its full life cycle. A considerable part of this element is found in cell sap. This calcium does not take much part in metabolic processes; it helps to neutralize excess acids of organic nature. The other part of calcium is in the plasma - here calcium works as a potassium antagonist, it works in the opposite direction compared to potassium, i.e. increases viscosity and reduces the hydrophilic properties of plasma colloids. In order for processes to proceed normally, the ratio of calcium and potassium directly in the plasma is important, since this ratio determines the colloidal characteristics of the plasma. Calcium is found in the nuclear substance and is therefore very important in the process of cell division. It also plays an important role in the formation of various cell membranes, with the greatest role in the formation of walls of root hairs, where it enters as pectate. If calcium is absent in the nutrient substrate, the growth points of the root and aerial parts are affected at lightning speed, due to the fact that calcium is not transported from old parts to young ones. The roots become slimy, and their growth proceeds abnormally or stops altogether. When grown in artificial culture using tap water, the absence of calcium is rare.

The element reaches the plant less than calcium or potassium. However, its role is very important, because the element is part of chlorophyll (1/10 of all magnesium in a cell is in chlorophyll). The element is vitally necessary for chlorophyll-free organisms, and its role does not end with photosynthetic processes. Magnesium is an important element necessary for respiratory metabolism; the element catalyzes many different phosphate bonds and transports them. Since phosphate bonds, which are rich in energy, are involved in many synthesizing processes, they simply cannot proceed without this element. If there is a lack of magnesium, chlorophyll molecules are destroyed, but the veins of the leaves remain green, and the areas of tissue located between the veins become paler. This is called spotty chlorosis, and it is quite common when the plant is deficient in magnesium.

The element is absorbed by the plant with the help of complex, organic compounds, as well as in the form of salts (soluble). The total iron content of the plant is small (hundredths of a percent). In plant tissues, iron is represented by organic compounds. It is also worth knowing that the iron ion can freely move from the ferrous form to the oxide form, or vice versa. Consequently, being present in various enzymes, iron participates in redox processes. The element is also part of respiration enzymes (cytochrome, etc.).

There is no iron in chlorophyll, but it is involved in its creation. If there is a lack of iron, chlorosis may develop - with this disease, chlorophyll is not formed, and the leaves become yellow. Due to the low mobility of iron in old leaves, it cannot be transported to young leaves. Therefore, chlorosis usually begins with young leaves.

If there is a lack of iron, photosynthesis also undergoes a change - plant growth slows down. To prevent chlorosis, you need to add iron to the nutrient substrate no later than 5 days after the onset of this disease; if you do this later, the likelihood of recovery is very low.