Every year a person more and more depletes the resources of the planet. It is not surprising that in recent years an assessment of how many resources one or another biocenosis can give is of great importance. Today, ecosystem productivity is crucial when choosing a management method, since the economic feasibility of work directly depends on the amount of products that can be obtained.
Here are the main questions that scientists face today:
- How much solar energy is available and how much is assimilated by plants, how is it measured?
- Which types of ecosystems have the highest productivity and which give the most primary products?
- What factors limit the amount of primary production locally and worldwide?
- What is the efficiency with which energy is converted by plants?
- What are the differences between assimilation efficiency, clean production, and environmental efficiency?
- How do ecosystems differ in biomass or autotrophic organisms?
- How much energy is available to people and how much do we use?
We will try to at least partially answer them within the framework of this article. First, let's deal with the basic concepts. So, ecosystem productivity is the process of accumulation of organic matter in a certain volume. What organisms are responsible for this work?
Autotrophs and heterotrophs
We know that some organisms are capable of synthesizing organic molecules from inorganic precursors. They are called autotrophs, which means "self-feeding." Actually, the productivity of ecosystems depends on their activity. Autotrophs are also referred to as primary producers. Organisms that are able to produce complex organic molecules from simple inorganic substances (water, CO2) most often belong to the class of plants, but some bacteria possess the same capabilities. The process by which they synthesize organics is called photochemical synthesis. As the name implies, photosynthesis requires sunlight.
We must also mention the pathway known as chemosynthesis. Some autotrophs, mainly specialized bacteria, can convert inorganic nutrients to organic compounds without access to sunlight. There are several groups of chemosynthetic bacteria in sea and fresh water, and they are especially common in environments with high levels of hydrogen sulfide or sulfur. Like chlorophyll-bearing plants and other organisms capable of photochemical synthesis, chemosynthetic organisms are autotrophs. However, the productivity of an ecosystem is more likely called the activity of vegetation, since it is it that is responsible for the accumulation of more than 90% of organic matter. Chemosynthesis plays an incomparably smaller role in this.
Meanwhile, many organisms can receive the necessary energy only by eating other organisms. They are called heterotrophs. In principle, they include all the same plants (they also “eat” the finished organics), animals, microbes, fungi and microorganisms. Heterotrophs are also called "consumers."
The role of plants
As a rule, the word "productivity" in this case refers to the ability of plants to store a certain amount of organic matter. And this is not surprising, since only plant organisms can convert inorganic substances to organic. Without them, life on our planet would be impossible, and therefore the productivity of the ecosystem is viewed from this perspective. In general, the question is posed extremely simply: so what mass of organic matter can plants store?
What biocenoses are the most productive?
Oddly enough, but human-created biocenoses are far from the most productive. The jungle, swamps, selva of large tropical rivers in this regard are far ahead of them. In addition, it is these biocenoses that neutralize a huge amount of toxic substances, which, again, fall into nature as a result of human activity, and also produce more than 70% of the oxygen contained in the atmosphere of our planet. By the way, many textbooks still claim that the oceans of the Earth are the most productive “granary”. Oddly enough, but this statement is very far from the truth.
Ocean Paradox
Do you know what the biological productivity of ecosystems of the seas and oceans is compared to? With semi-deserts! Large volumes of biomass are explained by the fact that it is water expanses that occupy most of the planet's surface. So the repeatedly predicted use of the seas as the main source of nutrients for all of humanity in the coming years is hardly possible, since the economic feasibility of this is extremely low. However, the low productivity of this type of ecosystem does not in any way detract from the importance of the oceans for the life of all living things, so they must be protected as carefully as possible.
Modern ecologists say that the possibilities of agricultural land are far from exhausted, and in the future we will be able to get more abundant crops from them. Particular hopes are placed on rice fields, which can give a huge amount of valuable organic matter due to their unique characteristics.
Biological Productivity Essentials
In general, ecosystem productivity is determined by the rate of photosynthesis and the accumulation of organic substances in a particular biocenosis. The mass of organic matter that is created per unit of time is called primary production. It can be expressed in two ways: either in Joules, or in the dry mass of plants. Gross production is called its volume, created by plant organisms for a certain unit of time, at a constant rate of photosynthesis. It should be remembered that part of this substance will go to the vital activity of the plants themselves. The organic matter left after this is the net primary productivity of the ecosystem. It is she who feeds heterotrophs, among which we are among you.
Is there an “upper limit” to primary production?
In short, yes. Let us briefly review how photosynthesis is effective in principle. Remember that the intensity of solar radiation reaching the earth's surface is highly dependent on location: the maximum energy return is characteristic of equatorial zones. It decreases exponentially as it approaches the poles. About half of the solar energy is reflected by ice, snow, oceans or deserts, absorbed by gases in the atmosphere. For example, a layer of atmospheric ozone absorbs almost all ultraviolet radiation! Only half of the light that enters the leaves of plants is used in the photosynthesis reaction. So the biological productivity of ecosystems is the result of converting an insignificant part of the sun’s energy!
What is secondary products?
Accordingly, the secondary product is called the growth of consumers (that is, consumers) over a certain period of time. Of course, ecosystem productivity depends on them to a much lesser extent, but it is this biomass that plays a crucial role in human life. It should be noted that secondary organics are separately counted at each trophic level. Thus, ecosystem productivity types are divided into two types: primary and secondary.
The ratio of primary and secondary products
As you might guess, the ratio of biomass to total plant mass is relatively small. Even in the jungle and swamps, this indicator rarely exceeds 6.5%. The more herbaceous plants in the community, the higher the rate of accumulation of organic matter and the greater the discrepancy.
On the rate and volume of formation of organic substances
In general, the limiting rate of formation of organic matter of primary origin depends entirely on the state of the photosynthetic apparatus of plants (PAR). The maximum value of photosynthesis efficiency, which was achieved in laboratory conditions, is 12% of the PAR value. Under natural conditions, a value of 5% is considered extremely high and practically does not occur. It is believed that on Earth the assimilation of sunlight does not exceed 0.1%.
Distribution of primary products
It should be noted that the productivity of the natural ecosystem is extremely uneven on a global scale. The total mass of all organic matter, which is formed annually on the surface of the Earth, is about 150-200 billion tons. Remember what we said about ocean productivity above? So, 2/3 of this substance is formed on land! Just imagine: gigantic, incredible volumes of the hydrosphere form three times less organic matter than the scanty part of the land, a considerable part of which is desert!
More than 90% of the accumulated organic matter in one form or another is eaten by heterotrophic organisms. Only an insignificant part of solar energy is stored in the form of soil humus (as well as oil and coal, the formation of which is even taking place today). In our country, the increase in primary biological production varies from 20 c / ha (near the Arctic Ocean) to more than 200 c / ha in the Caucasus. In desert areas, this value does not exceed 20 kg / ha.
In principle, on five warm continents of our world, the intensity of production is practically the same, almost: in South America, vegetation accumulates one and a half times more dry matter, due to excellent climatic conditions. There the productivity of natural and artificial ecosystems is maximum.
What provides nutrition to people?
Approximately 1.4 billion hectares are occupied on the surface of our planet by plantations of man-cultivated plants that provide us with food. This is approximately 10% of all ecosystems on the planet. Oddly enough, but only half of the output goes directly to people. Everything else is used as pet food and goes to the needs of industrial production (not related to the production of food). Scientists have been sounding the alarm for a long time: the productivity and biomass of the ecosystems of our planet are able to provide no more than 50% of human needs for protein. Simply put, half of the world's population lives in conditions of chronic protein starvation.
Record biocenoses
As we have already said, equatorial forests are characterized by the highest productivity. Just think about it: one hectare of such a biocenosis can account for more than 500 tons of dry matter! And this is far from the limit. In Brazil, for example, one hectare of forest produces from 1200 to 1500 tons (!) Of organic matter per year! Just think: up to two centners of organic matter per square meter! In the tundra on the same area no more than 12 tons are formed, and in the forests of the middle zone - within 400 tons. Agricultural enterprises in those parts are actively using this: the productivity of the artificial ecosystem in the form of a sugarcane field, which can accumulate up to 80 tons of dry matter per hectare, nowhere else can such crops yield physically. However, the gulfs of Orinoco, Mississippi, and also some areas of Chad differ slightly from them. Here, over a year, ecosystems “give out” up to 300 tons of matter per hectare of land!
