The natural world is unique and inconceivably diverse. Each year, scientists make more and more discoveries that reveal to us the extraordinary prospects of studying the world around us. But even quite familiar living organisms, which people have known about since time immemorial, are still able to surprise. Take, for example, lichens. 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 should be described in detail.
Difficulty learning
In general, they are quite difficult to study, since they are a symbiosis of completely different organisms. Each lichen is formed by a symbiosis of autotrophic algae and heterotrophic fungus. It is clear that first you have to study the biochemistry and life of each organism individually. This method of studying their physiology gives a lot of errors and errors, and therefore scientists have a huge number of questions, not all of which have answers. However, the researchers still managed to identify general patterns.
Internal structure
In general, the entire body of the 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). The cells of the photobiont colonies (algae) are randomly scattered throughout the body.
- Heteromeric (Peltigera canina). In the cross section, you can clearly see the layers of thalom (hyphae) and algae.
Most of all there are lichens, the structure of which is based on the last 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 mushroom prevents excessively quick drying (but it does not always help).
On the next layer is a colony of autotrophic algae. At the very center is the core of the lichen, which is a tight strand of intertwined fungal hyphae and autotroph colonies. This “core” has a dual function: on the one hand, lichen stores water in the core. On the other hand, it is a kind of skeleton of this organism. In the lower part there are rizins. This is a kind of mount with which the lichen clings to the substrate. It should be remembered that the complete set is not found in all species.
Some lichen species (cyanolic lichens) are characterized by the fact that their structure contains highly localized colonies of cyanogen algae. In these species, the separation into layers is especially well expressed. So how do lichens eat? The answer to this question is directly related to the features of
the photosynthesis process in them.
About the process of photosynthesis
There are thousands of studies 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 all the nutrients, 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 ordinary potatoes, the ratio will be 1:16.
But how to explain a completely comfortable life in such a Spartan environment? In general, there is nothing particularly complicated about this. The fact is that autotrophic higher plant organisms spend most of their lives awake, while lichens in some places stay almost half a year in a half-dried state, in suspended animation. Of course, a tiny amount of nutrients is enough for them to support life.
This is how lichens feed. Grade 7 in biological schools can study this topic in more detail, but even in this case, the standard educational program does not provide answers to many important questions. For example, when the process of formation of organic substances for nutrition is slower, and when - 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, when 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 be aware 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, bright northern forests. In those places where the light intensity is much higher, in the body of the symbiotic organism begins the intensive production of dark organic pigment (parietin), as well as substances specific only to lichens (atranorin, for example).
Organic substances obtained as a result of photosynthesis are completely similar to those of higher plants. They are used for trophic purposes. This is how lichens feed. The 7th grade of a comprehensive school studies the processes of their life activity very superficially, although this topic is large and extremely interesting. We bring to your attention extended information that may turn out to be not only interesting, but also useful.
Breathing process
It is easy to guess that the production of nutrients is directly dependent on respiration. Unlike photosynthesis in lichens, it is intense: 0.2–2.0 mg of ₂ per hour releases only one gram of a symbiotic organism. If you carefully read the information at the top of the article, then you probably understood that about 85-90% of the lichen mass is accounted for by the weight of the mycobiont. Simply put, it is the mushroom part that needs oxygen more than the autotrophic algae. Since lichens do not eat 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 respiration process directly depends 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, is preserved by the lichen under almost any conditions (suitable for life, of course). This process is possible at the following temperature ranges: from -15 to +30, +50 ° . But the optimal temperature regime is in the range from +15 to +20 ° . With cooling, the use of oxygen begins to prevail. And when the temperature rises above +35 degrees, both processes approximately equalize.
There is a known case when a lichen (a photo of this type is in the article), brought to one of the Moscow museums by the expedition of the Tsar’s Archaeological Society, calmly restored its activity by being placed by one of the employees in a flower pot with slightly moist soil. But by that time for almost 90 years he was in an absolutely dry, closed box for exhibits and most of the time he was deprived of even light!
It is not surprising that modern biology is so interested in these organisms. Lichens probably still have many secrets, the disclosure of which, perhaps, will significantly spur the development of medicine.
Scientists have proved that the basic principles of lichen respiration obey the same laws 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 the effects of drying, low and high temperatures. No wonder mosses and lichens can grow even in the Arctic.
Temperature mode
The temperature range from +10 to +25 degrees Celsius is most favorable for photosynthesis in lichens. But their ability to absorb carbon dioxide is preserved up 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 assimilation is almost greater than under 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 (crackling frosts) feel great when the warm season sets in.
Features of water metabolism
Researchers concluded 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 the 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, which will be sufficient for normal life, depends on the family. So, bushy lichens are capable of photosynthesis and the production of organic substances for nutrition with 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 more or less regular water supply is completely not guaranteed. In such conditions, any plant would die. Lichen, on the other hand, feels rather well even in the conditions of real deserts and the Arctic.
Fluid exchange regulation
It can be understood that the regulatory function of water metabolism in these organisms is structured in a completely different way than in higher plants. Since they practically have no specialized systems for this. For example, the assimilation of water in them occurs extremely quickly, but only due to its ordinary absorption by the entire surface of the body. You can do the simplest experiment: pour a small amount of water on the table and put a piece of napkin or toilet paper on the puddle.
As you can see, the water was immediately absorbed, since the structure of the paper has a good adsorption capacity. The same thing happens with lichens. So, we examined an episode with a long-dried specimen that was once brought by the expedition. When an employee put the lichen in a flower pot, he simply instantly absorbed such a volume of liquid that he had enough to restore his life.
Some bushy lichens are capable of absorbing a huge amount of liquid, the weight of which is up to 300% of their own. Other species (colems, leptogiums) thus increase in size by 400-3900%! If we talk about the minimum water content, then it is approximately 2% of the dry matter weight of lichen. Such a lichen (the photo you will find in this material) in appearance does not look like a living organism.
About the rate of return of water
As with toilet paper, the body of a symbiotic organism gives water quite quickly. In just an hour, the lichen, which has just absorbed almost a liter of liquid, can dry to a brittle condition. Thus, the "productivity" of these organisms is extremely cyclical: the production of trophic substances can dramatically change not only during the season, but also over one to two hours!
In recent years, scientists have learned that some species of lichens that live in the tundra (Evernia prunastri) may well use literally “crumbs” of 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 reproduction methods at once:
- Vegetative.
- Sexual.
- Asexual.
The fungus, that is, mycobiont, can multiply in all ways, while algae is capable of exclusively vegetative division. The spores of the fungus are located in special bags. Ascomycetic lichens for the breeding process use two main groups of fruiting bodies: apothecia and perithecy. Their characteristics are as follows:
- Apothecia is an ordinary bed of a rounded shape. On it are bags that are located between regular, endless hyphae. This openly located layer is called hymenium.
- Peritius resembles an almost completely closed structure of a spherical shape. Spores are released through special openings that are located on the surface of the fruit sphere.
Some species can also form asexual spores, pycnospores (pycnoconidia). The place of their formation are pycnidia. These are bags of a spherical or several pear-shaped, which are highly specialized hyphae. Pycnidia are easy to recognize because they look like black dots located on a bed.
When disputes wake up, they in suitable conditions quickly give rise to new hyphae, forming the body of a new lichen. They (hyphae) also penetrate the cells of autotrophic algae, after which the formation of a new organism actually ends.
Value
In general, mosses and lichens are of great importance. In the tundra and the Arctic desert, they are often the only
autotrophic organisms that can accumulate nutrient organic matter in extremely adverse 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 us to survive the winter, for example, moose and roe deer.