Ecology: the Biology of Interactions. 3.05. Ecological Balance

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3.04. Classification of Biomes

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.06. Ecosystem Productivity and its Measurement

3.05. Ecological Balance. The origin of life on Earth and its maintenance are the result of the transformation of a small part of solar energy. Living organisms can exist only by utilizing the energy flow passing through them. What processes ensure this flow? The main group of organisms on Earth can be considered phototrophs – bacteria and plants capable of photosynthesis. They draw the energy they need directly from the sun's radiation and convert it into a form accessible to other organisms. For heterotrophs (many bacteria, fungi, and animals), this form is various organic compounds. Our share of the energy flow from the sun passes through us with our food. The mechanisms that ensure the existence of chemotrophs are more complex. Consider, for example, the biocenosis of a "black smoker" – a place where hot water containing hydrogen sulfide emerges from the Earth's interior at the bottom of the ocean (Fig. 3.5.1). Where water from the interior, containing hydrogen sulfide, mixes with ocean water containing oxygen, chemosynthetic bacteria live, obtaining energy by oxidizing hydrogen sulfide. They live not only in water but also inhabit the bodies of large bivalve mollusks and worm-like animals of the group pogonophores – riftia (pogonophores were previously considered a separate phylum, but are now classified as annelid worms). These and other animals are fed upon by crustaceans and even fish. Can we conclude that such an ecosystem exists independently of the solar energy flow? Fig. 3.5.1. General view of a "black smoker," as well as riftia (Riftia pachyptila) and associated fauna in close-up. Of course not. The "black smoker" ecosystem uses dissolved oxygen, which is a product of photosynthesis. Using solar energy, phototrophs created a redox potential difference between the oxygen-rich atmosphere and the reducing interior. It is from this difference in chemical potentials that chemotrophs draw energy. It turns out that phototrophs somehow "feed" chemotrophs! However amazing such an interrelationship between two groups of organisms may seem, the most common interrelationships can appear even more amazing. Our planet is inhabited by two groups of living beings, for each of which the waste products or metabolic products of the other group are resources. This refers to autotrophs in general (including phototrophs) and heterotrophs, who correspond to each other like two halves of a broken plate. Naturally, such a correspondence cannot be accidental: it reflects an important regularity in the functioning of the biosphere. Since autotrophs and heterotrophs are inextricably linked, the most important characteristic of the biosphere is the ratio between their main functions: the creation and destruction of organic matter (Fig. 3.5.2). This ratio is called ecological balance (Table 3.5.1). Of course, the relationships shown in the figure are simplified. Organic matter is also created during chemosynthesis, and destroyed during glycolysis (anaerobic breakdown of carbohydrates in tissues; it is the consequences of this that cause muscle pain after strenuous exercise), fermentation, and combustion. Oxygen is not released, and sometimes even consumed in some bacterial types of chemosynthesis. During aerobic (oxygen) respiration, the rate of organic matter decomposition is much higher; the other two pathways of organic matter breakdown involve the work of a whole complex of functionally different transforming organisms. Fig. 3.5.2. Ecological balance in the biosphere is based on the equilibrium between photosynthesis and respiration. Table 3.5.1. Components of ecological balance.

Fig. III-5.2. The ecological balance in the biosphere is based on the equilibrium between photosynthesis and respiration

Table III-5.1. Components of the ecological balance

Photosynthesis

Anaerobic respiration (using other oxidizers)

CAM

Anaerobic respiration (using other oxidants)

Bacterial

Fermentation (restructuring of the substrate molecule)

Chemosynthesis

Despite the diversity of phenomena affecting the creation and destruction of organic matter, the ecological balance in the biosphere can be sufficiently accurately represented by the balance of the two most powerful processes that change the amount of organic matter – photosynthesis and respiration. Thus, to some extent, this balance can also be expressed through the equilibrium between oxygen and carbon dioxide in the atmosphere. A fundamental property of the biosphere is a positive balance sum. The oxygen-rich (i.e., oxidizing), rather than reducing, atmosphere on Earth is the result of a shift in balance in favor of prevailing photosynthesis. Part of the oxygen released during this process is consumed in the oxidation of reducing substances coming from the Earth's interior, and also dissipates into outer space. What happens to the organic matter equivalent to this oxygen? It accumulates in the ecosystem in the form of detritus (from Latin deterere – to grind) – organic matter in the process of decomposition. A component of detritus is humus – one of the products of organic matter decomposition. Its components, humic acids, have a variable composition; they include aromatic rings, nitrogen-containing groups, and hydrocarbon residues. The fate of the formed detritus can be varied. Part of it will be consumed by detritivores, which will oxidize it during their respiration. Another part of the detritus may end up in conditions where it becomes inaccessible for oxygen oxidation. Over time, such detritus will turn into fossil fuels: peat, shale, coal, and even gas and oil. Due to the fact that in the ecological balance, photosynthesis prevails over respiration, a significant amount of biogenic organic matter has accumulated in the Earth's crust, and a corresponding amount of oxygen has entered the atmosphere. The oxygen equivalent to the accumulated organic matter has already been consumed in chemical reactions and dispersed into space. From this, it follows that humanity fundamentally cannot burn all the reserves of organic matter accumulated in the Earth's crust – there simply won't be enough oxygen in the atmosphere for this. Conditions for the burial of organic matter varied in different periods of Earth's history. For example, in the Carboniferous period, swamps covered a large part of the planet, where large clubmosses and horsetails grew. Falling into the swampy liquid, trees ended up in anoxic conditions and eventually turned into coal (one of the resources on which our civilization exists). Is it a coincidence that during this time the largest terrestrial arthropods existed – dragonflies of the genus Meganeura with a wingspan of half a meter, as well as millipedes of the genus Arthropleura, which reached two meters in length? One of the factors limiting the maximum size of arthropods is the decrease in the efficiency of tracheal respiration with increasing body size. The high oxygen content in the Carboniferous atmosphere mitigated this limitation.

3.04. Classification of Biomes

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.06. Ecosystem Productivity and its Measurement