Every year, people are depleting the resources of the planet more and more. It is not surprising that recently an assessment of how many resources a particular biocenosis can provide has become of great importance. Today, the productivity of the ecosystem is of decisive importance when choosing a way of managing, since the economic feasibility of the work directly depends on the amount of production that can be obtained.
Here are the main questions scientists face today:
- How much solar energy is available and how much is assimilated by plants, how is it measured?
- Which types of ecosystems are the most productive and produce the most primary production?
- What factors limit primary production locally and globally?
- What is the efficiency with which plants convert energy?
- What are the differences between efficiencyassimilation, cleaner production and environmental efficiency?
- How do ecosystems differ in the amount of biomass or the volume of 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, the productivity of an ecosystem 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 activities. 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 have the same ability. The process by which they synthesize organics is called photochemical synthesis. As the name suggests, photosynthesis requires sunlight.
We should also mention the pathway known as chemosynthesis. Some autotrophs, mainly specialized bacteria, can convert inorganic nutrients into organic compounds without access to sunlight. There are several groups of chemosyntheticbacteria in sea and fresh water, and they are especially common in environments with a high content of hydrogen sulfide or sulfur. Like chlorophyll-bearing plants and other organisms capable of photochemical synthesis, chemosynthetic organisms are autotrophs. However, the productivity of the ecosystem is rather the activity of vegetation, since it is she who is responsible for the accumulation of more than 90% of organic matter. Chemosynthesis plays a disproportionately smaller role in this.
Meanwhile, many organisms can only get the energy they need by eating other organisms. They are called heterotrophs. In principle, these include all the same plants (they also “eat” ready-made 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 into organic ones. Without them, life itself on our planet would be impossible, and therefore the productivity of the ecosystem is considered from this position. In general, the question is extremely simple: so how much organic matter can plants store?
Which biocenoses are the most productive?
Oddly enough, but human-made biocenoses are far from being the most productive. Jungles, swamps, selva of large tropical rivers in this regardare far ahead. In addition, it is these biocenoses that neutralize a huge amount of toxic substances, which, again, enter 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 state that the Earth's oceans are the most productive "breadbasket". Oddly enough, but this statement is very far from the truth.
Ocean Paradox
Do you know what the biological productivity of the 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 mankind 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 in no way detracts from the importance of the oceans for the life of all living things, so they need to be protected as carefully as possible.
Modern environmentalists say that the possibilities of agricultural land are far from being exhausted, and in the future we will be able to get more abundant harvests from them. Particular hopes are placed on rice fields, which can produce a huge amount of valuable organic matter due to their unique characteristics.
Basic information about the productivity of biological systems
Overall ecosystem productivityis determined by the rate of photosynthesis and 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 its volume created by plant organisms in a certain unit of time, at a constant rate of the photosynthesis process. It should be remembered that part of this substance will go to the vital activity of the plants themselves. The remaining organic matter is the net primary productivity of the ecosystem. It is she who goes to feed heterotrophs, which include you and me.
Is there an "upper limit" to primary production?
In short, yes. Let's take a quick look at how efficient the process of photosynthesis is in principle. Recall that the intensity of solar radiation reaching the earth's surface is highly dependent on location: the maximum energy return is characteristic of the equatorial zones. It decreases exponentially as it approaches the poles. Approximately half of the solar energy is reflected by ice, snow, oceans or deserts, and absorbed by gases in the atmosphere. For example, the ozone layer of the atmosphere absorbs almost all ultraviolet radiation! Only half of the light that hits the leaves of plants is used in the photosynthesis reaction. So the biological productivity of ecosystems is the result of converting a tiny part of the sun's energy!
What is secondary production?
Accordingly, secondary products are calledthe growth of consumers (that is, consumers) for a certain period of time. Of course, the productivity of the ecosystem depends on them to a much lesser extent, but it is this biomass that plays the most important role in human life. It should be noted that secondary organics are separately calculated at each trophic level. Thus, the types of ecosystem productivity are divided into two types: primary and secondary.
Ratio of primary and secondary production
As you might guess, the ratio of biomass to total plant mass is relatively low. Even in the jungle and swamps, this figure 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.
About the rate and volume of formation of organic substances
In general, the limiting rate of formation of organic matter of primary origin completely depends 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%.
Primary production distribution
It should be noted that the productivity of the natural ecosystem is an extremely uneven thing across the planet. The total mass of all organic matter that is formed annually onsurface of the Earth, is about 150-200 billion tons. Remember what we said about the productivity of the oceans 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 a tiny part of the land, a large part of which are deserts!
More than 90% of the accumulated organic matter in one form or another is used as food for heterotrophic organisms. Only a tiny fraction of solar energy is stored in the form of soil humus (as well as oil and coal, which are being formed even today). On the territory of our country, the increase in primary biological production varies from 20 centners per hectare (near the Arctic Ocean) to more than 200 centners per hectare in the Caucasus. In desert areas, this value does not exceed 20 c/ha.
In principle, on the 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 feeds people?
Approximately 1.4 billion hectares on the surface of our planet are plantations of cultivated plants that provide us with food. This is approximately 10% of all ecosystems on the planet. Oddly enough, but only half of the resulting products go directly to human food. Everything else is used as pet food and goes tothe needs of industrial production (not related to the production of food products). Scientists have been sounding the alarm for a long time: the productivity and biomass of our planet's ecosystems can provide no more than 50% of humanity's needs for protein. Simply put, half of the world's population lives in conditions of chronic protein starvation.
Biocenoses-record holders
As we have already said, equatorial forests are characterized by the highest productivity. Just think about it: more than 500 tons of dry matter can fall on one hectare of such a biocenosis! 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: there are 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 belt - within 400 tons. Agricultural enterprises in those parts actively use this: the productivity of an artificial ecosystem in the form of a sugar cane field, which can accumulate up to 80 tons of dry matter per hectare, nowhere else can physically produce such yields. However, the Orinoco and Mississippi bays, as well as some areas of Chad, differ little from them. Here, for a year, ecosystems “give out” up to 300 tons of substances per hectare of area!
Results
Thus, the evaluation of productivity should be carried out on the basis of the primary substance. The fact is that secondary production is no more than 10% of this value, its value fluctuates greatly, and therefore a detailed analysisthis indicator is simply impossible.
