Lichens represent a complex object for physiological research, since they consist of two physiologically opposite components - a heterotrophic fungus and an autotrophic algae. Therefore, we first have to separately study the life activity of 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 “triple physiology” is a difficult path of research, and it is not surprising that there is still a lot of mystery hidden in the life activity of lichens. However, the general patterns of their metabolism have still been clarified.

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.

As measurements have shown, the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.

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. In this case, it is very significant that many species of lichens, especially in dry habitats, are rarely or at least very irregularly supplied with the optimal amount of intrathallal water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plants, which have a special apparatus capable of controlling the receipt and consumption of water. Lichens absorb water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively through the entire surface of their body and partly through 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 capable of absorbing water in very large quantities, usually up to 100 - 300% of the dry mass of the thallus, and some mucous lichens (collemas, leptogiums, etc.) even up to 800 - 3900%.

The minimum water content in lichens is natural conditions constitutes 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 lose all their water after 30–60 minutes and become fragile, i.e., the water content in the thallus becomes below the minimum required for active photosynthesis. This results in a peculiar “arrhythmia” of photosynthesis in lichens - its productivity varies throughout the day, season, and 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 thin snow cover.

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and they are the majority) accept nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens take some of the nitrogen compounds directly from the substrate - soil, tree bark, etc. Ecologically interesting group are 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. (species of xanthoria, physcia, caloplaca, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are capable of fixing atmospheric nitrogen, since the algae they contain have this ability. In experiments with such species (from the genera Collema, Leptogium, Peltigera, Lobaria, Stykta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogen compounds. Most of the nitrogen fixed by the algae is sent 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 absorption and distribution of nitrogen compounds fixed from the atmosphere by the phycobiont.

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 the slow growth is that the photobiont, often accounting for less than 10% of the lichen volume, takes upon itself to provide the mycobiont with nutrients. 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 crustacean forms is located along the edge of the lichen, in leafy and bushy ones at each tip.

Lichens are among the longest-lived organisms and can reach ages of several hundred years, and in some cases more than 4,500 years, such as Rhizocagron geographicum, living in Greenland.

Lichens are unique complex organisms, the thallus of which is a combination of a fungus and an algae that are in a complex relationship with each other, more often in symbiosis. Over 20 thousand species of lichens are known.

They differ from other organisms, including free-living fungi and algae, in shape, structure, nature of metabolism, special lichen substances, methods of reproduction, and slow growth (from 1 to 8 mm per year).

Structural features

Thallus lichens consists of intertwined fungal threads - hyphae, and algae cells (or threads) located between them.

There are two main types of microscopic structure of the thallus:

Homeomeric;
heteromeric.

On a cross section of a lichen homeomeric type there is an upper and lower cortex, which consists of a single layer of fungal cells. All inner part filled with loosely arranged fungal threads, between which are located algae cells without any order.

In lichen heteromeric type of algae cells are concentrated in one layer, which is called gonidial layer. Below it is the core, consisting of loosely arranged threads of the fungus.

The outer layers of the lichen are dense layers of fungal filaments called cortical layers. With the help of fungal threads extending from the lower cortical layer, the lichen is attached to the substrate on which it grows. In some species, the lower bark is absent and it is attached to the substrate by pith threads.

The algal component of lichen consists of species belonging to the blue-green, green, yellow-green and brown divisions. Representatives of 28 genera of them enter into symbiosis with fungi.

Most of these algae may be free-living, but some are found only in lichens and have not yet been found in a free state in nature. While in the thallus, the algae change greatly in appearance, and also become more resistant to high temperatures and can withstand prolonged drying. When cultivated on artificial media (separately from fungi), they acquire the appearance characteristic of free-living forms.

The thallus of lichens is varied in shape, size, structure, and colored in different colors. The color of the thallus is due to the presence of pigments in the hyphal membranes and fruiting bodies of lichens. There are five groups of pigments: green, blue, violet, red and brown. A prerequisite for the formation of pigments is light. The brighter the lighting in places where lichens grow, the brighter they are colored.

The shape of the thallus can also be varied. By external structure thallus lichens are divided into:

Scale;
leafy;
bushy.

U crustose lichens the thallus has the appearance of a crust, tightly fused with the substrate. The thickness of the crusts varies - from barely noticeable scale or powdery deposits to 0.5 cm, diameter - from a few millimeters to 20-30 cm. Scale species grow on the surface of soils, rocks, the bark of trees and shrubs, and exposed rotting wood.

Foliaceous lichens have the shape of a leaf-shaped plate located horizontally on the substrate (parmelia, wall goldenrod). Usually the plates are round, 10-20 cm in diameter. A characteristic feature of leafy species is the unequal color and structure of the upper and lower surfaces of the thallus. In most of them, on the lower side of the thallus, organs of attachment to the substrate are formed - rhizoids, consisting of hyphae collected in strands. They grow on the surface of the soil, among mosses. Foliage lichens are more highly organized forms compared to crustose lichens.

Fruticose lichens have the form of an erect or hanging bush and are attached to the substrate by small sections of the lower part of the thallus (cladonia, Icelandic lichen). In terms of level of organization, bushy species are the highest stage of thallus development. Their thalli come in different sizes: from a few millimeters to 30-50cm. Hanging thalli of fruticose lichens can reach 7-8 m. An example is the lichen that hangs in the form of a beard from the branches of larches and cedars in taiga forests (bearded lichen).

Reproduction

Lichens reproduce mainly by vegetative means. In this case, pieces are separated from the thallus, carried by wind, water or animals and, under favorable conditions, give rise to new thalli.

In leafy and fruticose lichens, for vegetative propagation, special vegetative formations are formed in the surface or deeper layers: soredia and isidia.

Soredia look like microscopic glomeruli, each of which contains one or more algae cells surrounded by fungal hyphae. Soredia are formed inside the thallus in the gonidial layer of foliose and fruticose lichens. The formed soredia are pushed out of the thallus, picked up and carried by the wind. Under favorable conditions, they germinate in new places and form thalli. About 30% of lichens reproduce by soredia.

Nutrition

The nutritional characteristics of lichens are associated with the complex structure of these organisms, consisting of two components that receive nutrients different ways. The fungus is a heterotroph, and the algae is an autotroph.

The algae in the lichen provides it organic substances produced by photosynthesis. The lichen fungus receives high-energy products from the algae: ATP and NADP. The fungus, in turn, with the help of filamentous processes (hyphae) acts as a root system. This is how the lichen gets water and mineral compounds, which are adsorbed from the soil.

Also, lichens are able to absorb water from the whole body environment, during fogs and rains. To survive they need nitrogen compounds. If the algal component of the thallus is represented by green algae, then nitrogen comes from aqueous solutions. When blue-green algae act as phycobionts, nitrogen fixation from atmospheric air is possible.

For the normal existence of lichens they are needed in sufficient quantities light and moisture. Insufficient lighting interferes with their development, as photosynthetic processes slow down and the lichens do not receive enough nutrients.

Light pine forests have become the optimal place for their life. Although lichens are among the most drought-resistant species, they still need water. Only in a humid environment do respiratory and metabolic processes take place.

The importance of lichens in nature and human life

Lichens are very sensitive to harmful substances, so they do not grow in places with high dust and air pollution. So, they are used as indicators of pollution.

They take part in the cycle of substances in nature. Their photosynthetic part is capable of producing organic matter in places where other plants cannot survive. Lichens play an important role in soil formation; they settle on lifeless rocky surfaces and, after dying, form humus. This creates favorable conditions for plant growth.

Feeding lichens are an important link in the food chain. For example, deer, roe deer, and moose feed on reindeer moss or moss. Serve as material for bird nests. Lichen manna or Aspicilia edible is used in cooking.

The perfume industry uses them to make perfumes last longer, and the textile industry uses them to dye fabrics. There are also known species with antibacterial properties, which are used in the manufacture of medicines to combat tuberculosis and furunculosis.

The natural world is unique and incredibly diverse. Every year, scientists make more and more new discoveries that reveal to us extraordinary prospects for studying the world around us. But even quite familiar living organisms, which people have known about since time immemorial, are still capable of surprising. Take lichens, for example. They are simple, but the features of their life 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, since they represent 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 we have to study the biochemistry and vital functions of each organism separately. This method of studying their physiology gives many errors and errors, and therefore scientists have a huge number of questions, not all of which have answers. However, the researchers were still able to identify general 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, science distinguishes the following types of lichens:

Homeomeric varieties (Collema). Cells of photobiont colonies (algae) are scattered in a chaotic manner throughout the body.
Heteromeric (Peltigera canina). In a cross section, the layers of thalome (hyphae) and algae can be clearly seen.

Most of all there are lichens, the structure of which is based on the last principle. In this case, the entire top layer is formed by a particularly dense plexus of fungal tissue, which protects the lichen body from negative impacts external environment. In addition, the mushroom prevents drying out too quickly (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 cord of intertwined hyphae of the fungus and autotroph colony. 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 a given organism. In the lower part there are rubbers. These are a kind of fastenings 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 their structure contains highly localized colonies of cyanalgae. In these species, the division into layers is especially well expressed. So how do lichens eat? The answer to this question is directly related to their characteristics.

About the process of photosynthesis

There are thousands of studies that are devoted specifically to the characteristics 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, 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 ordinary potatoes, the ratio will be 1:16.

But how can one explain a completely comfortable life in such spartan conditions? In general, there is nothing particularly difficult about this. The fact is that autotrophic higher plant organisms are “awake” for most of their lives, while lichens in some areas remain in a half-dried state, in suspended animation, almost the entire year. Of course, they only need a tiny amount of nutrients to maintain their vital functions.

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

What determines the intensity 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 light intensity is much higher, the body of the symbiotic organism begins intensive production of a dark organic pigment (parietin), as well as substances specific only to lichens (atranorin, for example).

Those obtained as a result of photosynthesis are completely similar to those of They are used for trophic purposes. This is how lichens feed. 7th grade secondary school studies the processes of their life activity very superficially, although this is a large and extremely interesting topic. We bring to your attention expanded information that may prove not only interesting, but also useful.

Breathing process

It’s easy to guess that the production of nutrients directly depends on breathing. Unlike photosynthesis in lichens, it is intense: 0.2-2.0 mg of CO₂ per hour is released by just one gram of the 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 a lichen is the weight of the mycobiont. Simply put, it is the fungal part that needs oxygen more, and not the autotrophic algae. Since lichens do not feed very regularly under normal conditions (the reason is harsh climatic conditions), a considerable part of the nutrients is stored in their tissues.

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

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

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

It is not surprising that modern biology is so interested in these organisms. Lichens probably still have many secrets, the revelation of which may significantly stimulate the development of medicine.

Scientists have proven that the basic principles of lichen respiration are subject to the same laws as in the case of higher autotrophic plants. But there are also differences, the main one being 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. It is not for nothing that mosses and lichens can grow even in Arctic conditions.

Temperature

The most favorable temperature range for photosynthesis in lichens is from +10 to +25 degrees Celsius. But they retain the ability to absorb carbon dioxide down to -25 degrees. This is a very remarkable feature of lichens, which distinguishes them from higher plants and even algae. At temperatures 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, whose trunks are literally torn apart by the harsh northern climate (biting frosts), feel great when the warm season begins.

Features of water exchange

The researchers came to the conclusion that lichens are distinguished by a special, extremely specific type of water metabolism. The fact is that the water in their body is contained in the spaces between the strong hyphae. When it freezes, it does not cause much harm, and the process of photosynthesis and nutrition continues to occur. However, when the temperature rises to +35 degrees Celsius or more, the process of photosynthesis practically stops, which fundamentally 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 when almost completely dehydrated. 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 at all guaranteed. Under such conditions, any plant would die. Lichen feels good even in real deserts and the Arctic.

Regulation of fluid metabolism

It can be understood that the regulatory function of water metabolism in these organisms is organized in a completely different way than in higher plants. Since they practically do not have any specialized systems for this. For example, their absorption 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 good adsorbing ability. The same thing happens in the case of lichens. So, we looked at an episode with a long-dried specimen that was once brought by an expedition. When the employee put the lichen in a flower pot, it simply instantly absorbed such a volume of liquid that it was enough to restore its vital functions.

Some fruticose lichens are capable of absorbing huge amounts of liquid, up to 300% of their own weight. Other species (collemas, leptogiums) increase in size by 400-3900% in this way! 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 water release

As in the case of toilet paper, the body of the symbiotic organism releases water quite 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 within one or two hours!

IN last years Scientists have learned that some species of lichen living in the tundra (Evernia prunastri) may well use literally “crumbs” sunlight, occasionally breaking through the layer of snow. Simply put, their photosynthesis does not stop even in winter.

Reproduction of lichens

In addition, the peculiarities of lichens are the presence of three methods of reproduction:

Vegetative.
Sexual.
Asexual.

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

The apothecium is a regular rounded bed. It contains bags that are located in the spaces between ordinary, ending-less hyphae. This open layer is called the hymenium.
The perithecia resembles an almost completely closed spherical structure. 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 spherical or somewhat pear-shaped sacs that represent highly specialized hyphae. Pycnidia are easy to recognize as they look like black dots located on the bed.

When the spores wake up, under suitable conditions they quickly give rise to new hyphae, forming the body of the 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 enormous importance. In the tundra and arctic desert They are often the only ones that can accumulate nutrient organic matter in extremely unfavorable conditions. Simply put, these organisms 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, for example, moose and roe deer to survive the winter.

As measurements have shown, the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.

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

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and they are the majority) accept nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. An ecologically interesting group consists of the so-called nitrophilous lichens, growing in habitats rich in nitrogenous compounds - on “bird stones”, where there is a lot of bird excrement , on tree trunks, etc. (species of xanthoria, physcia, kaloplaka, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are capable of fixing atmospheric nitrogen, since the algae they contain have this ability. In experiments with such species (from the genera Collema, Leptogium, Peltigera, Lobaria, Stykta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogen compounds. Most of the nitrogen fixed by the algae is sent 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 absorption and distribution of nitrogen compounds fixed from the atmosphere by the phycobiont.

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 the slow growth is that the photobiont, often accounting for less than 10% of the lichen volume, takes upon itself to provide the mycobiont with nutrients. In good conditions with optimal humidity and temperature, such as in foggy or rainy tropical forests, lichens grow several centimeters per year.

The growth zone of lichens in crustacean forms is located along the edge of the lichen, in leafy and bushy ones at each tip.

Lichens are among the longest-lived organisms and can reach ages of several hundred years, and in some cases more than 4,500 years, such as Rhizocagron geographicum, living in Greenland.

Reproduction of lichens

Lichens reproduce either by spores, which are formed by the mycobiont sexually or asexually, or vegetatively - by fragments of the thallus, soredia and isidia.

During sexual reproduction on the thalli of lichens, as a result of the sexual process, sexual sporulations are formed in the form of fruiting bodies. Among the fruiting bodies of lichens, apothecia, perithecia and gasterothecium are distinguished. Most lichens form open fruiting bodies in the form of apothecia - disc-shaped formations. Some have fruiting bodies in the form of a perithecia - a closed fruiting body that looks like a small jug with a hole at the top. A small number of lichens form narrow, elongated fruiting bodies called gasterothecium.

In apothecia, perithecia and gasterothecium, spores develop inside the bags - special sac-like formations. Lichens that form spores in bags are combined into large group marsupial lichens. They originated from fungi of the ascomycete class and represent the main evolutionary line of development of lichens.

In a small group of lichens, spores are formed not inside the bags, but exogenously, at the top of elongated club-shaped hyphae - basidia, at the ends of which four spores develop. Lichens with such spore formation are united in the group of basidiomycetes.

The female genital organ of lichens, the archicarp, consists of two parts. The lower part is called ascogon and is a spirally twisted hypha, thicker than other hyphae and consisting of 10 - 12 single or multinuclear cells. The trichogyne extends upward from the askogon - a thin elongated hypha that passes through the algae zone and the crustal layer and emerges on the surface of the thallus, rising above it with its sticky tip.

The development and maturation of the fruiting body in lichens is a very slow process that lasts 4–10 years. The formed fruiting body is also perennial, capable of producing spores for a number of years. How many spores can lichen fruiting bodies produce? It is estimated, for example, that in the lichen solorina, 31 thousand bursae are formed in an apothecia with a diameter of 5 mm, and 4 spores usually develop in each bursa. Therefore, the total number of spores produced by one apothecia is 124,000. During one day, from 1200 to 1700 spores are released from such an apothecia. Of course, not all spores ejected from the fruiting body germinate. Many of them, once in unfavourable conditions, die. For spores to germinate, they first need sufficient humidity and a certain temperature.

Asexual sporulation is also known in lichens - conidia, pycnoconidia and stylospores, which arise exogenously on the surface of conidiophores. In this case, conidia are formed on conidiophores developing directly on the surface of the thallus, and pycnoconidia and stylospores in special containers - pycnidia.

Of the asexual sporulations, lichens most often form pycnidia with pycnoconidia. Pycnidia are often found on the thalli of many fruticose and foliose lichens; less often they can be observed in crustose forms.

In each of the pycnidia, small single-celled spores - pycnoconidia - are formed in large quantities. The role of these widespread sporulations in the life of the lichen has not yet been clarified. Some scientists, calling these spores spermatia and pycnidia spermagonia, consider them male reproductive cells, although there is still no experimental or cytological data proving that pycnoconidia actually participate in the sexual process of lichens.

Vegetative propagation. If crustose lichens, as a rule, form fruiting bodies, then among the more highly organized foliose and bushy lichens there are many representatives that reproduce exclusively by vegetative means. In this case, formations that simultaneously contain fungal hyphae and algal cells are more important for the reproduction of lichens. These are soredia and isidia. They serve to reproduce the lichen as a whole organism. Once in favorable conditions, they directly give rise to a new thallus. Soredia and isidia are more common in foliose and fruticose lichens.

Soredia are tiny formations in the form of dust particles, consisting of one or more algae cells surrounded by fungal hyphae. Their formation usually begins in the gonidial layer. Due to the massive formation of soredia, their number increases, they put pressure on the upper bark, tear it and end up on the surface of the thallus, from where they are easily blown away by any movement of air or washed off with water. Clusters of soredia are called sorals. The presence and absence of soredia and sorals, their location, shape and color are constant for certain lichens and serve as a defining feature.

Sometimes, when lichens die, their thallus turns into a powdery mass consisting of soredia. These are the so-called leprosy forms of lichens (from the Greek word “lepros” - “rough”, “uneven”). In this case, it is almost impossible to identify the lichen.

Soredia, carried by wind and rainwater, once in favorable conditions, gradually form a new thallus. The regeneration of a new thallus from the soredia occurs very slowly. Thus, in species from the genus Cladonia, normal scales of the primary thallus develop from the soredia only after a period of 9 to 24 months. And for the development of a secondary thallus with apothecia it takes from one to eight years, depending on the type of lichen and external conditions.

Isidia are found in fewer lichen species than Soredia and Soralia. They are simple or coral-like branched outgrowths, usually densely covering the upper side of the thallus (see figure). Unlike sorals, isidia are covered on the outside with bark, often darker than thallus. Inside, under the bark, they contain algae and fungal hyphae. Isidia easily break off from the surface of the thallus. Breaking off and spreading with the help of rain and wind, they, like soredia, can, under favorable conditions, form new lichen thalli.

Many lichens do not form apothecia, soredia and isidia and reproduce by sections of the thallus, which are easily broken off from the fragile lichens in dry weather by the wind or animals and are carried by them. The reproduction of lichens by sections of the thallus in the Arctic regions is especially widespread, representatives of the genera Cetraria and Cladonia, many of which almost never form fruiting bodies.

Lichen is a single organism containing unicellular algae and a fungus. This symbiosis is extremely beneficial for the existence of the entire organism as a whole. After all, while the fungus absorbs water and dissolved mineral salts, the algae produces organic substances from carbon dioxide and water through the process of photosynthesis under the influence of sunlight. Lichen- an unpretentious organism. This gives lichens the opportunity to settle first in places where there is no other vegetation. After them, humus appears, on which other plants can live.

Lichens found in nature are extremely varied in appearance and color. On old spruce trees you can often see hanging tousled beards of lichens called lichen, or bearded lichen. And on the bark of some trees, in particular aspen, orange round-shaped plates of wall goldenrod lichen are sometimes attached. Deer lichen is a grayish whitish small bush. This plant grows in dry pine forests, and in dry weather it makes a characteristic crunching sound if you walk on it.

Lichens are widespread. They are unpretentious, so they live in various, sometimes harsh conditions. Lichens can be found on bare rocks and stones, on the bark of trees, on fences, and sometimes even on the soil. In the northern regions, and more specifically, in the tundra, lichens inhabit vast areas, for example, deer lichen. You can also often find lichens in the mountains.

In the structure of lichens There are features that allow you to combine them into a separate group. If you examine a thin section of a lichen under a microscope, you will notice that it structural elements are transparent threads, between which there are rounded green cells. Scientists have found that the colorless threads are the mycelium of the fungus, and the green cells are nothing more than unicellular algae. Thus, one lichen organism combines two different organisms- an algae and a fungus that interact so closely that they form a whole organism.

The relationship between two organisms in the body of a lichen allows it to adapt favorably to environmental conditions. Thanks to the mycelium, water and carbon dioxide are absorbed, and organic substances are formed in the algae’s body. In some cases, the fungus can feed on algae that are found in the body of the lichen. Lichen absorbs liquid over the entire surface of the body, mainly after rain, but also from dew and fog. And nutrients are absorbed from everywhere - from the air, soil and even from settling dust. All types of lichen do not need to create special favorable conditions for life. They are unpretentious and hardy. During a period of drought, the lichen dries out to such an extent that it breaks at the slightest touch, and after rain it comes to life again. It is in connection with such features of life that lichens are found in such barren areas where other plants are not able to survive.

Lichens play an important role in nature and human economy. Since lichens are unpretentious, they are the first to settle in areas where there is no other vegetation. Having finished my life cycle on bare rocks and stones, lichens die, leaving behind humus on which other representatives of the plant kingdom can develop. Thus, in this case, the importance of lichens is that they create the soil for the life of other plants. Deer lichen has highest value in the human economy. This lichen, which grows over a vast area in the tundra, is the main food for reindeer.

Lichens
(lower plants)

Structure

This is a unique group of lower plants, which consist of two different organisms - a fungus (representatives of ascomycetes, basidiomycetes, phycomycetes) and algae (green - cystococcus, chlorococcus, chlorella, Cladophora, palmella are found; blue-green - nostoc, gleocapsa, chroococcus), forming a symbiotic cohabitation , characterized by special morphological types and special physiological and biochemical processes. Some lichens were thought to contain bacteria (Azotobacter). However, later studies did not confirm their presence in lichens.

Lichens differ from other plants in the following ways:

1. Symbiotic cohabitation of two different organisms - a heterotrophic fungus (mycobiont) and an autotrophic algae (phycobiont). Lichen cohabitation is permanent and historically conditioned, and not accidental, short-term. In a true lichen, the fungus and algae come into close contact; the fungal component surrounds the algae and can even penetrate its cells.

2. Specific morphological forms of external and internal structure.

3. The physiology of fungi and algae in the lichen thallus differs in many ways from the physiology of free-living fungi and algae.

4. The biochemistry of lichens is specific: they form secondary metabolic products not found in other groups of organisms.

5. Reproduction method.

6. Attitude to environmental conditions.

Morphology. Lichens do not have a typical green color, they do not have a stem or leaves (this is how they differ from mosses), their body consists of a thallus. The color of lichens is grayish, greenish-gray, light or dark brown, less often yellow, orange, white, black. The coloring is due to pigments that are found in the membranes of the fungal hyphae, less often in the protoplasm. There are five groups of pigments: green, blue, violet, red, brown. The color of lichens may also depend on the color of lichen acids, which are deposited in the form of crystals or grains on the surface of the hyphae.

Lichens are classified as crustacean, or crustaceous, leafy, and bushy.

U scale the thallus has the appearance of a powdery, lumpy or smooth skin that tightly fuses with the substrate; about 80% of all lichens belong to them. Depending on the substrate on which crustose lichens grow, they are distinguished:

epilithic, developing on the surface of rocks;

epiphleoid - on the bark of trees and shrubs;

epigeic - on the soil surface,

epixyl - on rotting wood.

Thallus lichen can develop inside a substrate (stone, tree bark). There are crustose lichens with a spherical thallus (the so-called nomadic lichens).

U leaf lichens the thallus has the form of scales or rather large plates, which are attached to the substrate in several places with the help of bundles of fungal hyphae. The simplest thallus of leaf lichens has the appearance of one large rounded leaf-shaped blade, reaching a diameter of 10-20 cm. Such a thallus is called monophyllous. It is attached to the substrate in its central part with the help of a thick short stalk called a gomph. If the thallus consists of several leaf-shaped plates, it is called polyphilic. A characteristic feature of the leaf thallus of lichens is that its upper surface differs in structure and color from the lower. Among leaf lichens there are also non-attached, nomadic forms.

U fruticose lichens the thallus consists of branched threads or stems, fused with the substrate only at the base; grow upward, to the side, or hang down - “bearded” lichens. The thallus of fruticose lichens has the appearance of an erect or hanging bush, less often of unbranched erect outgrowths. This is the highest stage of development of the thallus. The height of the smallest is only a few millimeters, the largest - 30-50 cm (sometimes 7-8 m - long usnea, hanging in the form of a beard from the branches of larches and cedars in taiga forests). Thallus come with flat and rounded lobes. Sometimes large bushy lichens in tundra and highland conditions develop additional attachment organs (hapters), with the help of which they grow to the leaves of sedges, grasses, and shrubs. In this way, lichens protect themselves from being torn off strong winds and storms.

Internal structure lichens. Based on their anatomical structure, lichens are divided into two types.

· In one of them, the algae are scattered throughout the entire thickness of the thallus and are immersed in the mucus that the algae secretes (homeomeric type). This is the most primitive type. This structure is typical for those lichens whose phycobiont is blue-green algae - nostoc, gleocapsa, etc. They form a group of slimy lichens.

· In another (heteromeric type), several layers can be distinguished under a microscope on a cross section. On top is the upper cortex, which has the appearance of intertwined, tightly closed mushroom hyphae. Underneath it, the hyphae lie more loosely, with algae located between them - this is the gonidial layer. Below, the mushroom hyphae are located even more loosely, the large spaces between them are filled with air - this is the core. The core is followed by the lower crust, which is similar in structure to the upper crust. Bundles of hyphae pass through the lower bark from the pith and attach the lichen to the substrate.

Crusted lichens do not have a lower bark and the fungal hyphae of the cores grow directly with the substrate.

In bushy radially built lichens, at the periphery of the cross section there is a bark, under it there is a gonidial layer, and inside there is a core. The bark performs protective and strengthening functions. Attachment organs are usually formed on the lower crustal layer of lichens. Sometimes they look like thin threads consisting of a single row of cells. They are called rhizoids. Rhizoids can join together to form rhizoidal cords.

In some leaf lichens, the thallus is attached using a short stalk (gomph), located in the central part of the thallus.

The algae zone performs the function of photosynthesis and accumulation of organic matter. The main function of the core is to conduct air to the algae cells containing chlorophyll. In some fruticose lichens, the pith also performs a strengthening function.

The organs of gas exchange are pseudocyphellae (ruptures in the cortex, visible to the naked eye as white spots of irregular shape). On the lower surface of leaf lichens there are round, regular-shaped white depressions - these are cyphellae, also organs of gas exchange. Gas exchange also occurs through perforations (dead sections of the crustal layer), cracks and breaks in the crustal layer.

Nutrition

Hyphae play the role of roots: they absorb water and mineral salts dissolved in it. Algae cells form organic substances and perform the function of leaves. Lichens can absorb water over the entire surface of the body (they use rainwater, moisture from fogs). An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont receive nitrogen compounds from aqueous solutions when their thallus is saturated with water, partly directly from the substrate. Lichens that have blue-green algae (especially nostoc algae) as a phycobiont are capable of fixing atmospheric nitrogen.

Reproduction

Lichens reproduce either by spores, which are formed by the mycobiont sexually or asexually, or vegetatively - by fragments of the thallus, soredia and isidia.

During sexual reproduction, sexual sporulation in the form of fruiting bodies is formed on the lichen thalli. Among the fruiting bodies in lichens, apothecia are distinguished (open fruiting bodies in the form of disc-shaped formations); perithecia (closed fruiting bodies that look like a small jug with a hole at the top); gasterothecium (narrow, elongated fruiting bodies). Most lichens (over 250 genera) form apothecia. In these fruiting bodies, spores develop inside bags (sac-like formations) or exogenia, at the top of elongated club-shaped hyphae - basidia. The development and maturation of the fruiting body lasts 4-10 years, and then for a number of years the fruiting body is capable of producing spores. A lot of spores are formed: for example, one apothecium can produce 124,000 spores. Not all of them germinate. Germination requires conditions, primarily certain temperature and humidity.

Asexual sporulation of lichens - conidia, pycnoconidine and stylospores that arise exogenously on the surface of conidiophores. Conidia are formed on conidiophores developing directly on the surface of the thallus, and pycnoconidia and stylospores are formed in special containers - pycnidia.

Vegetative propagation is carried out by thallus bushes, as well as by special vegetative formations - soredia (specks of dust - microscopic glomeruli, consisting of one or several algae cells surrounded by fungal hyphae, forming a fine-grained or powdery whitish, yellowish mass) and isidia (small, variously shaped outgrowths of the upper surface of the thallus , the same color as it, look like warts, grains, club-shaped outgrowths, and sometimes small leaves).

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

Lichens grow incredibly slowly, the fastest - only 30 mm per year. however, the symbiosis allows it to survive for very long periods of time. In fact, the species discovered in western Greenland is thought to be about 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 additional 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 threads called plus and minus. The strings fuse to create a core that is divided into shapes several times. 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 found everywhere, and people have used them for various purposes since ancient times (as food for pets, as medicine and food, for dyeing fabrics). However, for a long time people did not know what kind of organism it was. This 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 shades, from grayish green to stronger, more vibrant colors, with hints of red and yellow. Here you can see more 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 classified as both the plant kingdom and the fungal kingdom.

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

The body of the lichen is a thallus. Different types of lichens have different thallus, it differs in shape and structure, color, and size. Most lichens have a thallus several centimeters long, but some lichens are 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 food that will be used by the lichen as a whole. Thus, the algae or cyanobacteria are found 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: crustose, foliose and bushy. Crustose lichens look like crusts stuck to the surface, usually of rock or stone. Leafy lichen has a thallus in the form of plates. The foliose lichen thallus is attached to the surface by a thick short stalk. Fruticose lichen looks like a bush. The bush can rise above the surface or hang.

Reproduction of lichens occurs with the release of small grains formed by some algae and part of the fungus. These grains are called breast. Since lichen consists 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 by the type of fungi and lichen forms. But this classification does not have much biological value, since we have two completely different genomes from an evolutionary point of view.

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, resulting in a single organism. The fungal hyphae are intertwined in the thallus, with cells of green algae or cyanobacteria located between them. These cells can be located either singly or 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 - rhizines

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

Algae have the ability to perform 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 a fungus is associated with cyanobacteria, its diet can utilize atmospheric nitrogen.

Thus, lichen 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). An analogy can be drawn. 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 occur separately in nature.

Fungal hyphae absorb water with dissolved minerals, and algae or cyanobacteria carry out photosynthesis and form organic matter.

Lichens reproduce by sections of the 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 can grow on rocks, walls of houses, in the desert and tundra. And, of course, they are found everywhere in forests. However, lichens are very sensitive to pollution. If the air is smoky and contains harmful gases, the lichens die. Therefore, lichens can serve as indicators of environmental cleanliness.

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

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

Reindeer moss is a lichen that serves as food for reindeer. Some types of lichens are edible for humans, others have antimicrobial properties and are used medicinally.

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, so they are considered bioindicators of pollution as they can easily absorb toxic substances present in the air. Thus, the presence of lichens indicates low levels of pollution, while its disappearance indicates worsening environmental pollution.

Methods of feeding lichens

The lichen thallus, the plant apparatus of a lichen, devoid of roots, stomata and cuticle, is completely and exclusively dependent on the atmosphere, water and sun for its nutrition. Thanks to this feature, lichens managed to invade and colonize all existing territories. Their decomposition provides humus and allows other plants to settle. Animals will then graze on these plants and the life cycle will settle down. This phenomenon is observed in lava fields after volcanic eruption, the first pioneers are actually lichens.

Another characteristic feature of lichens is the origin of their expansion: regeneration, 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 metabolism. Algae and fungi, protecting each other, have colonized all environments over the millennia, arid zones, tropical or even frosty ones. Some lichens can remain submerged for 9 months, while others grow out of the rain; of the species are calcicols of other calcifications, some, like others, prefer shade.

As measurements have shown, the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.

All these features are especially interesting for studying different environmental conditions using lichens. These are unmistakable indicators. Depending on the substrates, 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 secondary secondary deposits, more or less branched, bearing fruiting bodies. thallus is gelatinous when in wet it has the consistency of gelatin 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. In this case, it is very significant that many species of lichens, especially in dry habitats, are rarely or at least very irregularly supplied with the optimal amount of intrathallal water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plants, which have a special apparatus capable of controlling the receipt and consumption of water. Lichens absorb water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively through the entire surface of their body and partly through 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 capable of absorbing water in very large quantities, usually up to 100 - 300% of the dry mass of the thallus, and some slimy lichens (collemas, 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 answer to photosynthesis is not a fungus.

Attached to the substrate, holding water, supplying water, doing photosynthesis, 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.

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

What is the connection between these organisms? Name a representative with a crust insole. Name the deputy with a protracted insole. Name a representative with a sleeve insole. How many millions of lichens will grow each year? What is the function of fungi in lichen? What is the function of algae in a lichen? fungal algae, cyanobacteria symbiosis lichen geographic gecko bubble netted reindeer 1mm-10mm shape, fixation, water photosynthesis, supplied by org. substances.

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and they are the majority) accept nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. Ecologically, they are so-called nitrophilic lichens that grow in habitats rich in nitrogenous compounds - on “bird stones”, where there is a lot of bird excrement, on tree trunks, etc. (species of xanthoria, physcia, caloplaca, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are capable of fixing atmospheric nitrogen, since the algae they contain have this ability. In experiments with such species (from the genera Collema, Leptogium, Peltigera, Lobaria, Stykta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogen compounds. Most of the nitrogen fixed by the algae is sent 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 absorption and distribution of nitrogen compounds fixed from the atmosphere by the phycobiont.

Natural history for primary schools: zoology and botany. Completely ignored is the subtle and ubiquitous porch of the lichen world that surrounds us in almost every terrestrial environment. At first glance, lichens are something completely ordinary, which is not even worth noticing. 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 the slow growth is that the photobiont, often accounting for less than 10% of the lichen volume, takes upon itself to provide the mycobiont with nutrients. In good conditions, with optimal humidity and temperature, such as in foggy or rainy tropical forests, lichens grow several centimeters per year.

The growth zone of lichens in crustacean forms is located along the edge of the lichen, in leafy and bushy ones at each tip.

Lichens are among the longest-lived organisms and can reach ages of several hundred years, and in some cases more than 4,500 years, such as Rhizocagron geographicum, living in Greenland.