A lichen is a living organism formed by the symbiosis of a fungus and an algae. Algae can be green algae or blue-green algae. Blue green algae are actually bacteria, they are called cyanobacteria. So a lichen can be a symbiosis of 1) fungus and algae, or 2) fungus, algae and cyanobacteria, or 3) fungus and cyanobacteria.

Lichens grow incredibly slowly, the fastest growing at only 30 mm per year. however, the symbiosis allows it to survive for very long periods of time. In fact, the species found in western Greenland is thought to be around 500 years old. During periods of drought, the lichen survives because the fungus can store two to three times its weight in water in the hyphae. They can also store sugars and extra nutrients taken up by algae during times of drought.

Although they survive together, the algae and fungus reproduce separately. Alga reproduces asexually through mitosis, which is the division of a cell into two identical daughter cells. The fungus reproduces sexually; hyphae contain two additional strands called plus and minus. The strings are fused to create a core that is divided several times into shapes. When mature, the spores are carried by the wind to germinate in a new location.

The number of different types of lichens is about 25 thousand species. Lichens are found on all continents of the Earth, even in Antarctica.

Lichens are ubiquitous and have been used by people since ancient times for a variety of purposes (as pet food, as medicine and food, to dye fabrics). However, people did not know for a long time what kind of organism it was. It became known only in the middle of the 19th century.

It is common to find crusts greenish in walls, rocks, and tree trunks. These are lichens. They can come in a variety of hues, from greyish green to a stronger and more vibrant color, with hints of red and yellow. Here you can see other photos of various lichens.

The special structure of lichens does not make it possible to unambiguously identify them to any one kingdom of the living world. They can be attributed both to the kingdom of plants and to the kingdom of fungi.

Lichens grow very slowly, but live a very long time. Lichen can live for hundreds or even thousands of years.

The body of the lichen is a thallus. In different types of lichens, the thallus is different, it differs in shape and structure, color, size. Most lichens have a thallus several centimeters long, but there are lichens about a meter long.

The photobiont "part" of a lichen can be an algae formed by a single cell or a cyanobacterium. It is this organism that produces the food that will be used by the lichen as a whole. Thus, the algae or cyanobacteria are inside the lichen, protected on the outside by a fungus that forms a thin layer that prevents water loss.

There are three types of lichens depending on the appearance of the thallus: scale, leafy and bushy. Crustaceous lichens are like crusts stuck to a surface, usually rock or stone. Leafy lichen has a thallus in the form of plates. The thallus of the foliose lichen is attached to the surface with a thick short stalk. Bushy lichen looks like a bush. The bush can rise above the surface or hang.

Lichen reproduction occurs with the release of small grains formed by some algae and part of the fungus. These grains are called breasts. Since the lichen is composed of two different organisms, we cannot classify them into biological groups, and even their identification is very difficult. Classification of lichen species is made mainly according to the type of fungi and lichen forms. But this classification is of little biological value, since we have two completely different genomes from an evolutionary standpoint.

Lichens come in white, green, yellow, blue, gray and other colors.

The symbiosis of the fungus and algae in the body of the lichen is very close, which results in a single organism. The hyphae of the fungus are intertwined in the thallus, cells of green algae or cyanobacteria are located between them. These cells can be located both singly and in groups.
The structure of a lichen using the example of Sticta fuliginosa: a - cortical layer, b - gonidial layer, c - core, d - lower cortex, e - rhizins

It is much better to see the lichen as an interaction between two organisms. Lichens are formed by an association of fungi and algae or fungi and cyanobacteria. In most lichens, fungi are ascomycetes and algae are chlorophytes. The outer layers of lichens are formed by fungal hyphae, while the innermost layer is formed by algae cells as well as fungal hyphae.

Algae have the ability to do photosynthesis and, thanks to this, can produce substances that are used in the nutrition of the fungus. In contrast, the fungus provides protection against algae, in addition to providing water and minerals. When the fungus is associated with cyanobacteria, atmospheric nitrogen can be used in its diet.

The lichen thus combines two very different organisms. The fungus feeds heterotrophically (absorbs ready-made organic substances), and the algae feeds autotrophically (synthesizes organic substances from inorganic ones). You can draw an analogy. Mycorrhiza is a symbiosis between higher plants and fungi, and lichen is a symbiosis between lower plants and fungi. However, in lichen, the symbiosis is much closer. After all, the types of fungi that are part of lichens cannot exist at all without algae. Although most lichen algae are found separately in nature.

Hyphae of the fungus absorb water with dissolved minerals, and algae or cyanobacteria carry out photosynthesis and form organic substances.

Lichens reproduce by patches of thallus and spores.

The symbiosis of algae and fungus allows the lichen to live in a variety of environmental conditions that are unsuitable for life. Lichens are able to grow on rocks, walls of houses, in the desert and tundra. And, of course, they are ubiquitous in forests. However, lichens are very sensitive to pollution. If the air is smoky, harmful gases are present in it, then the lichens die. Therefore, lichens can serve as indicators of purity. environment.

But there is some controversy about these studies, since lichens are considered pioneers, which means that they settle first in new conditions, thereby creating conditions for other organisms to live. We also know that lichens can withstand extreme temperatures, as well as water scarcity, in rocks exposed to the sun, ice, deserts, bare soil, dry trunks, etc. this ability to survive in inhospitable places is exclusively a fungus. This is an association with a fungus that allows algae to survive in rather unfriendly places.

Lichens are the first to colonize rocky ground. Subsequently, they participate in the destruction of rocks, dissolving the substrate. When dying, lichens participate in the formation of soil, along with other organisms.

Yagel is a lichen that serves as food for reindeer. Some types of lichens are edible to humans, others have antimicrobial properties and are used in medicine.

Lichens are organisms that reproduce asexually through small fragments that have fungal hyphae and associated algal cells. These fragments are called dreams and can be carried by the wind to distant places. These organisms are extremely sensitive to environmental changes, which is why they are considered bioindicators of pollution because they can easily absorb toxic substances that are present in the air. Thus, the presence of lichens is indicative of a low level of pollution, while its disappearance is indicative of worsening environmental pollution.

Lichen feeding methods

Lichens are a complex object for physiological studies, since they consist of two physiologically opposite components - a heterotrophic fungus and an autotrophic algae. Therefore, it is first necessary to separately study the vital activity of the myco- and phycobiont, which is done with the help of cultures, and then the life of the lichen as an integral organism. It is clear that such a “triple physiology” is a difficult path of research, and it is not surprising that there is still a lot of mystery in the life of lichens. However general patterns their metabolism is still elucidated.

The lichen thallus, the plant apparatus of the lichen, devoid of root, stomata, and cuticle, depends entirely and exclusively on the atmosphere, water, and sun for its nourishment. Thanks to this feature, lichens managed to introduce and colonize all existing territories. Their decomposition provides humus and allows other plants to settle. Then the animals will graze on these plants and the life cycle will settle. This phenomenon is observed in lava fields after a volcanic eruption, the first pioneers are actually lichens.

Another characteristic feature of lichens is the origin of their expansion: rebirth, the ability to quickly, reversibly and periodically change from a dry state to a hydrated state. When climatic conditions are not favorable, they stop or slow down the metabolism. Algae and fungi, protecting each other, have colonized all environments for millennia, arid zones, tropical or even frosty. Some lichens can stay submerged for up to 9 months while others grow out of the rain; of the species are calcicoli of other calcifications, some, like others, prefer the shade.

Quite a lot of research is devoted to the process of photosynthesis in lichens. Since only a small part of their thallus (5 - 10% of the volume) is formed by algae, which, nevertheless, is the only source of supply of organic substances, a significant question arises about the intensity of photosynthesis in lichens.

Measurements have shown that the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.

All these features are of particular interest for studying various ecological conditions with the help of lichens. These are unmistakable indicators. Depending on the substrate, very different types of lichens are found: soil on the ground, corticols on tree bark, lignicols on dead wood, saxicols on rocks, walls and various compact materials. They do not release nutrients from these carriers, but are very sensitive to their mechanical and chemical properties. From a primary crustacean, picky or leafy thallus, and minor secondary deposits, more or less branched, bearing fruiting bodies. thallous gelatinous, when wet it has a gelatinous consistency due to the presence of cyanobacteria evenly distributed in the thallus.

For normal photosynthetic activity, the thallus must contain a certain amount of water, depending on the anatomical and morphological type of lichen. In general, in thick thalli, the optimal water content for active photosynthesis is lower than in thin and loose thalli. At the same time, it is very significant that many species of lichens, especially in dry habitats, are generally rarely or at least very irregularly supplied with an optimal amount of intrathallus water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plantshaving a special apparatus that can control the receipt and consumption of water. Lichens assimilate water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively with the entire surface of their body and partly with the rhizoids of the underside. This absorption of water by the thallus is a simple physical process, such as the absorption of water by filter paper. Lichens are able to absorb water in very large quantities, usually up to 100 - 300% of the dry mass of the thallus, and some slimy lichens (kollems, leptogiums, etc.) even up to 800 - 3900%.

When dry, it is hard and crumbly. These different morphologies can be found on all types of substrates, soil, rocks, trees, branches and dead wood. Sponges and algae live together in symbiosis What is symbiosis? Answer Mutual coexistence of 2 or more organisms. Which lichen does not tolerate photosynthesis? The response to photosynthesis is not a fungus.

Attaches to the substrate, holding water, supplying water, do photosynthesis by adding organic matter, algae, mushroom fibers. Rice. 1: cut the lichen. Representative: geographical lichen Fig. 2: Geographical lichens. Representative: Tertiary bubble Fig. 3: Tertiary blister Fig. 5: Tertiary bubbling.

The minimum water content in lichens under natural conditions is approximately 2 - 15% of the dry mass of the thallus.

The release of water by the thallus also occurs quite quickly. Lichens saturated with water in the sun after 30-60 minutes lose all their water and become brittle, i.e., the water content in the thallus becomes lower than the minimum required for active photosynthesis. From this follows a kind of “arrhythmia” of lichen photosynthesis - its productivity changes during the day, season, a number of years, depending on general environmental conditions, especially hydrological and temperature ones.

On the stumps on the branches of mountain forests, representatives: deer deer, cupcake; strands Fig. 6: Rope Fig. 4: Reindeer deer. Reproduction: Insoles of insoles or algae clusters: pioneers of life, biological weathering, reindeer herding, shelters sensitive to polluted air. How can you find worlds according to lichens? Answer Lichens grow predominantly on the north side.

What is the relationship between these organisms? Name a representative with a crust insole. Name a deputy with a lingering insole. Name a representative with a sleeve insole. How many million lichens will grow annually? What is the function of fungi in lichen? What is the function of algae in lichen? fungal algae, cyanobacteria symbiosis lichen geographic gecko bubble mesh reindeer 1mm-10mm shape, fixation, water photosynthesis, supplied org. substances.

There are observations that many lichens photosynthesize more actively in the morning and evening hours and that photosynthesis continues in them in winter, and in ground forms even under a thin snow cover.

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and most of them) perceive nitrogen compounds from aqueous solutionswhen their thalli are saturated with water. It is possible that lichens also take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. Ecologically they make up the so-called nitrophilic lichens growing in habitats rich in nitrogenous compounds - on "bird stones", where there is a lot of bird excrement, on tree trunks, etc. (types of xanthoria, fiscia, caloplaki, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are able to fix atmospheric nitrogen, since the algae contained in them have this ability. In experiments with such species (from the genera collema, leptogium, peltiger, lobaria, stikta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogenous compounds. Most of the nitrogen fixed by the algae goes to the mycobiont, and only a small part is used by the phycobiont itself. There is evidence that the mycobiont in the lichen thallus actively controls the assimilation and distribution of nitrogenous compounds fixed from the atmosphere by the phycobiont.

Natural History for Primary Schools: Zoology and Botany. The imperceptible and ubiquitous porch of the lichen world that surrounds us in almost every earthly environment is completely ignored. At first glance, lichens are something completely ordinary, which is not even worth noticing. And yet it is a brilliant combination of two life forms, a plant that can cope with very harsh conditions. From hot deserts, inhospitable rocks to weevils. In fact, it is sometimes difficult to understand, but for inquisitive eyes that almost never look back, the miniature world opens the door to great secrets.

The rhythm of life described above is one of the reasons for the very slow growth of most lichens. Sometimes lichens grow only a few tenths of a millimeter per year, mostly less than one centimeter. Another reason for slow growth is that the photobiont, often making up less than 10% of the lichen volume, takes over the supply of nutrients to the mycobiont. In good conditions, with optimal humidity and temperature, for example in foggy or rainy tropical forests, lichens grow several centimeters per year.

The growth zone of lichens in scale forms is located along the edge of the lichen, in foliose and fruticose forms at each top.

Lichens are among the longest living organisms and can be several hundred years old, and in some cases over 4500 years old, such as Rhizocapron geographicum living in Greenland.

Lichens are a group of living organisms.

Their body is built using a combination of two microorganisms that are in a symbiotic relationship: a fungus (mycobiont) and an algae (phycobiont or cyanobacteria).

general characteristics

The science of lichenology, which is a department of botany, is engaged in the study of this species.

For a long time, lichens were a mystery to scientists, although their use was widespread throughout various sectors of human life. And only in 1867 the structure of this species was scientifically proven. Scientists-lichenologists were engaged in this.

On the this moment scientists have discovered more than 25 thousand species, but they all have a similar external and internal structure. The features by which each species should be distinguished are based on structural features.

What does a lichen look like

As already mentioned, the main part of the species is the body, which is distinguished by a variety of shapes and colors. In this case, growth can be a plate, a crust that looks like a leaf, in the form of a bush, tube or ball.

The height of the plant also varies within fairly large limits: from 3 centimeters to the height of a person.

Types and names of lichens

Lichenology has divided lichens into several groups in connection with the shape of the thallus:

In addition, based on the place where they grow, there are:

• epigeic (mainly on a land basis);
• epiphytic (on a tree base);
• epilithic (on stone).

Features of the internal structure

It seems possible to see the structure of the lichen under a magnifying device. A lichen is an organism consisting of a part of a fungus - a mycelium and algae, intertwined with each other.

Depending on how the cells of algae and fungi are distributed among themselves, another classification is distinguished:

• homeomeric, in which the phycobiont is located randomly among the cells of the mycobiont;
• heteromeric, in which there is a clear separation into layers.

Lichens with a layered structure are found everywhere and have the following layer structure:

1. The cortical layer is composed of mycobiont cells and protects from external influences, especially from drying out.
2. Superficial or gonidial: contains only phycobiont cells.
3. The core consists of a fungus, performs the function of a skeleton, and also contributes to the retention of water.
4. The lower cortex performs the function of attachment to the base.

It is worth noting: in some species, some types of layers may be absent or have a modified structure.

Where do they live

Lichens are distinguished by their ability to adapt to absolutely any conditions of existence. For example, they grow on bare stones, rocks, walls and roofs of buildings, tree bark, etc.

This is due to the mutually beneficial cooperation of the myco- and phycobionts included in the composition. The vital activity of one complements the existence of the other, and vice versa.

How do lichens eat

Nutrition is provided by symbiotes. Since fungi do not have the function of autotrophic nutrition, in which the process of converting organic components from inorganic ones takes place, algae supply the body with the necessary elements.

This happens through photosynthesis. And the fungus supplies the lichen with mineral salts, which it absorbs from the incoming fluid. In this way, the process of symbiosis occurs.

How they breed

They reproduce in two ways:

1. Sexual - is carried out due to spore formation.
2. Vegetative - for this, there are soredia (an algae cell braided with a thread of mycelium, which is carried by the wind) and isidia (outgrowths that form the surface layer of the thallus).

The value of lichens in nature and human life

They have the following positive effects:

Lichens are famous for their longevity, because only the growth period can reach 4 thousand years.

As a result, they can be used to approximately determine the age of the rock.

It is popular to use them as a fertilizer in the agricultural industry. In addition, their use began in ancient times. Lichens were used as natural dyes.

Lichens are unique view, carrying a mass useful properties and qualities applicable in virtually any area of ​​human life.

Lichen feeding methods

Lichen feeding methods

Lichens are a complex object for physiological research, since they consist of two physiologically opposite components - a heterotrophic fungus and an autotrophic algae. Therefore, it is first necessary to separately study the vital activity of the myco- and phycobiont, which is done with the help of cultures, and then the life of the lichen as an integral organism. It is clear that such a “triple physiology” is a difficult path of research, and it is not surprising that there is still a lot of mystery in the life of lichens. However, the general patterns of their metabolism are still elucidated.

Quite a lot of research is devoted to the process of photosynthesis in lichens. Since only a small part of their thallus (5-10% of the volume) is formed by algae, which nevertheless is the only source of supply of organic substances, a significant question arises about the intensity of photosynthesis in lichens.

Measurements have shown that the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants. So, for example, the ratio of assimilation productivity in foliose lichens to assimilation productivity in potatoes is on average 1: 16. But this intensity still ensures the normal life of lichens, which is easily explained if we take into account the presence of frequent periods of significant environmental depression (drying) and greater plasticity the entire metabolic apparatus of lichens, which allows them to endure these periods and quickly return to life even under conditions of low temperature, low carbon dioxide content, etc., in which other plants die or cease to live. This, of course, should also explain the slow growth of lichens.

The process of photosynthesis in lichens depends on many environmental factors (light, temperature, humidity, etc.). The chloroplasts of algae cells in the thallus under the hyphae crust receive somewhat less light than the chloroplasts under the epidermis in the leaves of higher plants. But this difference is small, but the crustal layer covering the thallus performs the function of protecting against excessively intense radiation in open places. The maximum intensity of photosynthesis is observed in lichens at illumination in the range of 4000-23,000 lux - such illumination indicators are typical for most of their habitats in the tundra, forest tundra, light coniferous forests. And where the illumination is higher, the thallus is protected by dark pigments contained in the crustal layer (for example, parietin) and lichen substances (for example, atranorin).

The temperature optimum for photosynthesis for most lichens is in the range from +10 to +25 °C, but they absorb carbon dioxide at both higher (up to +35 °C) and lower temperatures (even down to -25 °C). Particularly noteworthy is the ability of lichens to assimilate CO2 at low temperatures. Many experiments have confirmed the intensive absorption of carbon dioxide by lichens at -5, -10 ° C and even at lower temperatures. Under such conditions, assimilation does not occur in most higher plants, ice accumulates in the intercellular spaces, dehydration and cell damage occur. Apparently, in the thalli of lichens there is a completely different type of water regime, and the water, which is mainly between the hyphae, turning into ice, does not serve as an obstacle to their vital activity and the absorption of carbon dioxide. At the same time, high temperatures (above +35 ° C) stop their photosynthesis process, and in this respect, lichens are very different from higher plants, in which photosynthesis continues even at temperatures from +30 to +50 ° C.

For normal photosynthetic activity, the thallus must contain a certain amount of water, depending on the anatomical and morphological type of lichen. In general, in thick thalli, the optimal water content for active photosynthesis is lower than in thin and loose thalli. At the same time, it is very significant that many species of lichens, especially in dry habitats, are generally rarely or at least very irregularly supplied with an optimal amount of intrathallus water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plants that have a special apparatus that can control the receipt and consumption of water. Lichens assimilate water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively with the entire surface of their body and partly with the rhizoids of the underside. This absorption of water by the thallus is a simple physical process, such as the absorption of water by filter paper. Lichens are able to absorb water in very large quantities, usually up to 100-300% of the dry mass of the thallus, and some slimy lichens (kollems, leptogiums, etc.) even up to 800-3900%.

The minimum water content in lichens in natural conditions is approximately 2-15% of the dry weight of the thallus.

The release of water by the thallus also occurs quite quickly. Lichens saturated with water in the sun after 30-60 minutes lose all their water and become brittle, that is, the water content in the thallus becomes lower than the minimum required for active photosynthesis. From this follows a kind of "arrhythmia" of lichen photosynthesis - its productivity changes during the day, season, a number of years, depending on general environmental conditions, especially hydrological and temperature.

There are observations that many lichens photosynthesize more actively in the morning and evening hours and that photosynthesis continues in them in winter, and in ground forms even under a thin snow cover.

The respiration of lichens is directly related to photosynthotic activity. It is shown that it is generally lower than that of higher plants, and averages 0.2-2.0 mg of CO2 released per 1 g of dry mass per 1 hour. Since in most lichens in the thallus, the fungal component , then it is believed that the intensity of respiration is mainly determined by the vital activity of the mycobiont. Respiration, like photosynthesis, depends on the water content in the thallus and on temperature. In general, an increase in water content to maximum saturation is accompanied by a successive increase in the intensity of respiration, and, conversely, with a decrease in water content, respiration weakens, still remaining with very small amounts of water in the thallus, even in its air-dry state. The temperature range at which lichen respiration is possible is wide: from -15 to +30, +50 °С, while the optimum respiration is usually observed in the range from +15 to +20 °С. With an increase in temperature from 0 to +35 °C, the intensity of respiration increases, and at +35 °C, the absorption and release of CO2 are balanced.

AT general processes respiration in lichens obey the same patterns as in other autotrophic plants, but there are also some features. The main one is low respiration rate. On the other hand, lichens are characterized by high respiration resistance to desiccation and low temperatures. This can be considered an adaptation to life in unfavorable habitats - the polar arctic deserts, on the one hand, and true arid deserts, on the other hand.

It is generally accepted that organic substances synthesized in the lichen thallus by the phycobiont are used by the fungal component of the lichen. But how the transfer of assimilates from phycobiont to mycobiont proceeds and in the form of what compounds was not known until recently. Only the use of radioactive carbon C14 brought some clarity to this complex issue. It has now been established that in the cells of a phycobiont from blue-green algae (mainly in nostoc) glucose is formed during photosynthesis (according to some recent data, glucosan, which, under the influence of some fungal enzyme, turns into glucose), which is absorbed by the fungus, turning into mannitol. In lichens with a phycobiont of green and yellow-green algae, polyhydric alcohols are mobile carbohydrates: in trebuxia(Trebouxia) and myrmecia(Myrmecia) - ribit, at trentepolie(Trentepohlia) and phycopeltisa(Phycopeltis) - erythritol, heterococcus(Heterococcus), hyalococcus(Hyalococcus) and trochiscia(Trochiscia) - sorbitol. Interestingly, only lichen phycobionts secrete polyhydric alcohols; they were not found in free-living algae. This indicates that the symbiosis alters the algae's metabolism. Further, it is obvious that the mycobiont actively affects algal cells, stimulating the release of assimilates necessary for their nutrition. But how? There is no definite answer to this question yet. It is believed that the fungus secretes organic acids that lower the pH, which in turn causes an increase in the permeability of the algal cells. But it can also be some kind of enzyme that hydrolyzes the products of assimilation, which under other conditions would be used to build the cell walls of algae. There are observations that lichen substances (for example, usnic acid - see more in the section "Chemical composition of lichens") also increase the permeability of algal cells.

Finally, some scientists suggest that stimulation of the phycobiont by fungal hyphae in the thallus occurs simply through physical contact.

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and most of them) perceive nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens also take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. An ecologically interesting group is the so-called nitrophilic lichens growing in habitats rich in nitrogenous compounds - on "bird stones", where there is a lot of bird excrement , on the trunks of roadside trees, etc. (types of xanthoria, fiscia, kaloplaki, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are able to fix atmospheric nitrogen, since the algae contained in them have this ability. In experiments with such species (from the genera collema, leptogium, peltiger, lobaria, stikta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogenous compounds. Most of the nitrogen fixed by the algae goes to the mycobiont, and only a small part is used by the phycobiont itself. There is evidence that the mycobiont in the lichen thallus actively controls the assimilation and distribution of nitrogenous compounds fixed from the atmosphere by the phycobiont.

As for other nutritional components involved in the metabolism of lichens, especially mineral elements, the ability of lichens to accumulate in their thallus those substances that, in such quantities, would seem to be unnecessary for its normal activity, is striking. So, for example, the definitions showed that the common ground lichen diplochistes(Diploschistes scruposus) can contain in its thallus 10 times more zinc (9.34% dry matter) than is available in the same volume of soil from a given habitat. The biological meaning of such a selective accumulation of individual substances has not been established.

Plant life: in 6 volumes. - M.: Enlightenment. Edited by A. L. Takhtadzhyan, Chief Editor Corresponding Member USSR Academy of Sciences, prof. A.A. Fedorov. 1974 .

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The natural world is unique and inconceivably diverse. Every year, scientists make more and more new discoveries that open up extraordinary prospects for studying the world around us. But even quite familiar living organisms, which a person has known from time immemorial, are still capable of surprising. Take, for example, lichens. They are simple, but the features of their life activity are very unusual.

Do you know how lichens eat? This is a truly unique process that is worth describing in detail.

Difficulties of cognition

In general, they are quite difficult to study, as they are a symbiosis of completely different organisms. Each lichen is formed by a symbiosis of an autotrophic algae and a heterotrophic fungus. It is clear that first you have to study the biochemistry and vital activity of each organism separately. This method of studying their physiology gives many errors and inaccuracies, and therefore scientists have a huge number of questions, not all of which have answers. However, the researchers still managed to identify common patterns.

Internal structure

In general, the entire body of a lichen is a massive interweaving of fungal hyphae, inside which colonies of autotrophic algae are located. Today in science, the following types of lichens are distinguished:

• Homeomeric varieties (Collema). Cells of photobiont colonies (algae) are randomly scattered throughout the body.
• Heteromeric (Peltigera canina). On the cross section, the layers of thalom (hyphae) and algae can be clearly seen.

Most of all there are lichens whose structure is based on the latter principle. In this case, the entire upper layer is formed by a particularly dense plexus of fungal tissue, which protects the body of the lichen from the negative effects of the external environment. In addition, the fungus prevents excessively rapid drying (but this does not always help).

The next layer contains a colony of autotrophic algae. In the very center is the core of the lichen, which is a tight strand of intertwined hyphae of the fungus and the colony of the autotroph. This “rod” has a dual function: on the one hand, the lichen stores water in the core. On the other hand, it is a kind of skeleton of this organism. Risins are located in the lower part. This is a kind of attachment with which the lichen clings to the substrate. It should be remembered that the complete set is not found in all species.

Some types of lichens (cyanolichens) are characterized by the fact that in their structure there are highly localized colonies of cyanoalgae. In these species, the division into layers is especially pronounced. So how do lichens eat? The answer to this question is directly related to their features.

About the process of photosynthesis

There are thousands of studies that are devoted specifically to the features of photosynthesis in these symbiotic organisms. Since about 10-15% of their volume is occupied by algae, which gives them almost everything, many questions arise about the intensity of the process. Oddly enough, but the simplest measurements clearly showed that the intensity of photosynthesis in lichens is much lower when compared with higher autotrophic plants. So, when drawing an analogy with an ordinary potato, the ratio will be 1:16.

But how to explain a completely comfortable life in such Spartan conditions? In general, there is nothing particularly difficult in this. The fact is that autotrophic higher plant organisms are “awake” for most of their lives, while lichens in some areas are in a half-dried state, in suspended animation, for almost the entire year. Of course, a meager amount of nutrients is quite enough for them to maintain their vital activity.

This is how lichens eat. Grade 7 in biological schools can study this topic in more detail, but even in this case, the answers to many important questions are standard educational program does not give. For example, when is the process of formation of organic matter for nutrition slower, and when is it a little faster?

What determines the rate of photosynthesis in lichens?

It should be noted that the intensity of this process depends on many different factors. It is also important that chloroplasts, being covered with a dense layer of hyphae, receive much less light than similar formations in higher autotrophic plants and even algae. In principle, this difference is not so significant.

You should know that the maximum value of the photosynthesis process is observed at illumination in the range of 4000-23000 lux. This can be found in the main habitats of lichens: tundra, forest-steppe, light northern forests. In those areas where the intensity of illumination is much higher, in the body of a symbiotic organism, intensive production of a dark organic pigment (parietin), as well as substances specific only to lichens (atranorine, for example), begins.

Obtained as a result of photosynthesis are completely similar to those of Oni and are used for trophic purposes. This is how lichens eat. 7th grade secondary school studies the processes of their vital activity very superficially, although this topic is large and extremely interesting. We bring to your attention extended information that may be not only interesting, but also useful.

Breathing process

It is easy to guess that the production of nutrients directly depends on breathing. In contrast to photosynthesis in lichens, it is intense: 0.2–2.0 mg CO₂ per hour releases only one gram of a symbiotic organism. If you carefully read the information at the top of the article, you probably realized that about 85-90% of the mass of the lichen falls on the weight of the mycobiont. Simply put, it is the fungal part that needs more oxygen, and not the autotrophic algae. Since lichens do not feed very regularly under normal conditions (the reason is harsh climatic conditions), a large part of the nutrients are stored in their tissues.

Like photosynthesis, the process of respiration is directly dependent on the percentage of water.

You should know that the minimum level of respiration, which is necessary to obtain a certain amount of energy from nutrients, the lichen retains under almost any conditions (suitable for life, of course). This process is possible at the following temperature ranges: from -15 to +30, +50 °С. But optimal temperature regime is in the range from +15 to +20 °С. With cooling, the use of oxygen begins to predominate. And when the temperature rises above +35 degrees, both processes are approximately aligned.

There is a known case when a lichen (a photo of this species is in the article), brought to one of the Moscow museums by an expedition of the Tsarist Archaeological Society, calmly restored its vital activity, being placed by one of the employees in a flower pot with slightly damp earth. But by that time it had been in a completely dry, closed box for exhibits for almost 90 years, and most of the time it was even deprived of light!

It is not surprising that modern biology is so interested in these organisms. Lichens probably still have a lot of secrets, the disclosure of which, perhaps, will significantly spur the development of medicine.

Scientists have proven that the basic principles of lichen respiration follow the same patterns as in the case of higher autotrophic plants. But there are differences, the main of which is a slightly different priority between the absorption of oxygen and the release of carbon dioxide. In addition, they are phenomenally resistant to drying, low and high temperatures. No wonder mosses and lichens can grow even in the Arctic.

Temperature regime

The most favorable for photosynthesis in lichens is the temperature range from +10 to +25 degrees Celsius. But their ability to absorb carbon dioxide remains down to -25 degrees. This is a very remarkable feature of lichens, which distinguishes them from higher plants and even algae. At temperatures ranging from -5 to -10 degrees, the intensity of carbon dioxide absorption is almost greater than in more comfortable conditions. In many plants, in this case, ice forms in the intercellular space, which simply breaks the cells.

In contrast, lichens on trees, the trunks of which are literally torn apart by severe northern climate(bitter frosts), feel great when the warm season comes.

Features of water exchange

The researchers came to the conclusion that lichens are distinguished by a special, extremely specific type of water exchange. The fact is that the water in their body is contained in the spaces between strong hyphae. When it freezes, it does not bring much harm, and the process of photosynthesis and nutrition continues to occur. However, even when the temperature rises to +35 degrees Celsius or more, the process of photosynthesis practically stops, which radically distinguishes lichens from plants.

The amount of water that will be enough for normal life depends on the family. Thus, fruticose lichens are capable of photosynthesis and the production of organic substances for nutrition in almost complete dehydration. The thicker the body, the more moisture can accumulate in it, the less it evaporates.

This is especially important for lichens, since in most cases they grow in very difficult conditions, when a more or less regular supply of water is not guaranteed at all. Under such conditions, any plant would die. Lichen, on the other hand, feels good even in the conditions of real deserts and the Arctic.

Regulation of fluid exchange

It can be understood that the regulatory function of water metabolism in these organisms is arranged in a completely different way than in higher plants. Since they practically do not have any specialized systems for this. For example, their assimilation of water occurs extremely quickly, but only due to its ordinary absorption by the entire surface of the body. You can conduct a simple experiment: pour a small amount of water on the table and place a piece of napkin or toilet paper on the puddle.

As you can see, the water was instantly absorbed, since the structure of the paper has a good adsorbing capacity. The same thing happens in the case of lichens. So, we considered an episode with a dried-up specimen that was once brought by an expedition. When the employee put the lichen into the flower pot, it simply instantly absorbed such a volume of liquid that was enough for him to restore his life.

Some fruticose lichens are able to absorb huge amounts of liquid, up to 300% of their own weight. Other species (collems, leptogiums) thus increase in size by 400-3900%! If we talk about the minimum water content, then it is approximately 2% of the weight of the dry matter of the lichen. Such a lichen (you will find a photo in this material) looks completely different from a living organism.

About the rate of return of water

As in the case of toilet paper, the body of the symbiotic organism gives off water rather quickly. In just an hour, a lichen that has just absorbed almost a liter of liquid can dry out to a brittle state. Thus, the "productivity" of these organisms is extremely cyclical: the production of trophic substances can change dramatically not only during the season, but also for one or two hours!

AT last years scientists have learned that some species of tundra lichen (Evernia prunastri) may well use literally "crumbs" sunlight, occasionally breaking through a layer of snow. Simply put, their photosynthesis does not end even in winter.

Lichen reproduction

In addition, the features of lichens are the presence of three methods of reproduction at once:

• Vegetative.
• Sexual.
• Asexual.

A fungus, that is, a mycobiont, can reproduce in all ways, while an algae is capable of exclusively vegetative division. The spores of the fungus are located in special bags. Ascomycete lichens for the reproduction process use two main groups of fruiting bodies: apothecia and perithecia. Their characteristics are as follows:

• Apothecium is a common rounded bed. On it are bags that are located in the intervals between the usual, non-terminating hyphae. This open layer is called the hymenium.
• The perithecium is similar to an almost completely closed structure of a spherical shape. Spores are released through special holes that are located on the surface of the fruit sphere.

Some species can also form asexual spores, pycnospores (pycnoconidia). The place of their formation is pycnidia. These are sacs that are spherical or somewhat pear-shaped and are highly specialized hyphae. Pycnidia are easy to recognize, as they look like black dots located on the bed.

When the spores wake up, they quickly give rise to new hyphae under suitable conditions, forming the body of a new lichen. They (hyphae) also penetrate into the cells of autotrophic algae, after which the formation of a new organism actually ends.

Meaning

In general, mosses and lichens are of great importance. in the tundra and arctic wilderness they are often the only ones that can accumulate nutrient organic matter in extremely unfavorable conditions. Simply put, it is these organisms that are the source of food for those few herbivores that can live in such harsh places. In addition, only lichens on trees, even in our climate, often allow elk and roe deer, for example, to survive the winter.

Lichens- amazing living formations that baffle adherents of strict biological taxonomy. Indeed, to which taxon do organisms belong, which, as if as a result of the experiment of a crazy scientist, are a union mushrooms(also "hanging" between plants and animals) with algae or cyanobacteria? The hyphae of the fungus form the basis of the body of the lichen, while the internal filling is the cells of the algae. Thanks to them, more precisely, their ability to photosynthesis, this strange organism receives energy for the production of nutrients.

Fossilized lichens are a rare find due to the vulnerability of their bodies; Devonian lichens that are about 400 million years old are considered reliable. Now the group has about 25 thousand species. Lichens are extremely unpretentious, they endure cold weather without loss. humid climate but also heat and drought.

So what characteristics do lichens have?

Where do lichens live?

You can meet lichens not only in the forests and mountains of Asia, Europe and both Americas, but even in Antarctica and the Arctic. They are comfortable in huge temperature limits: from -50 to +60 degrees. Photosynthesis does not stop even in the cold! Lichens are able to live on bare stones, being content with a small amount of nutrients. Lichens also live on glass, fabrics and metal!

Everything is suitable for their nutrition: droplets of moisture from fog, dew, particles of dust. True, lichens are extremely sensitive to polluted air - exceeding harmful substances destroys them.

Survive in difficult environmental conditions leafy help lichen species rhizoids, sometimes equipped with special plates or drops of mucus for better attachment to the base.

The structure and nutrition of lichens

1. Lichen wall goldfish(the genus xanthoriaceae) must have been seen by many - it lives on tree trunks, on stones, representing a collection of tiny funnels of bright yellow color. This xanthoria belongs to heteromeric lichens, that is, those whose body is quite clearly divided into several layers. If you make a thin section of xanthoria, you can see woven hyphae of fungi in the upper and lower parts (crusts). The lower hyphae attach the lichen to tree bark and other substrates.
2. Hyphae are also present in the middle part, but they are loosely woven, and unicellular algae are located between them. And the innermost layer is represented by hyphae, between which lie air-filled voids.
3. At homeomeric lichens (kollema, leptogium), algae cells are not localized in one layer, but are distributed randomly, sometimes singly, sometimes forming chains.

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