Nitrogen cycle Definition Process and Steps

 Nitrogen Cycle

Nitrogen (N) is an abundant chemical element, found in many areas. In the total volume of the earth’sNitrogen Cycle atmosphere, its percentage is almost 78%, far exceeding oxygen. For this reason, the nitrogen cycle is, the biogeochemical of nature, considered significant in the stability of existence.

Nitrogen cycle – an Overview

The nitrogen cycle is the process by which nitrogen circulates and recirculates through the globe. It comprises a biogeochemical circulation of organic and abiotic processes that provides nitrogen to living forms. In addition, it allows this element to continue to be maintained in the biosphere. It shows interrelationships between living beings, autotrophs and heterotrophs, the tiny decomposing organisms of organic matter, and the large volume of atmospheric N.

  • What is the nitrogen cycle?
  • features
  • Process
  • Stages
  • The nitrogen cycle in water
  • Alterations
  • Consequences
  • Profits
  • Organisms that participate in the nitrogen cycle
  • Importance

What is the nitrogen cycle?

The nitrogen cycle encompasses a group of episodes on which the constitutive dynamic equilibrium of the biosphere is based. A brief summary is as follows:

Nitrogen is attached to plants by germs and other prokaryotes using metabolic processes. It becomes usable organic aggregates, such as ammonia, which plants use for the production of organic molecules.

This component of plants reaches herbivorous animals and then carnivores, distributing itself to the various rungs of the food pyramid. When expelled from the body by urine, rich in ammonia, nitrogen returns to the soil, restarting the cycle again.

The ammonia deposited on the ground, either by the urine of the animals or by the work of the fixing miasmas, is used. It will serve as sustenance for other microorganisms with nitrifying action. These break down ammonia and mold it into nitrites and nitrates.

Said oxidized chemical combinations will serve as food for different prokaryotes with de-nitrifying assimilation, which will alter their molecules. Thus they will acquire the vigor to exist and release again, to the atmosphere, the volatile nitrogen. In this way the cycle restarts.


Among the characteristics of the nitrogen cycle, the following stand out:

  • The ability to appear with different chemical aspects is caused by the depletion of electrons. Thanks to this, he presents varied “behaviors”,
  • The chemical aspects of this compound can be: Of organic origin, they are found in the amino acids and proteins of the body. Of inorganic origin: There are ammonia, ammonium ion, nitrites, and nitrates. Ammonia is essential in the development of plants and tissues of all living things.
  • Another remarkable characteristic is its relationship with germs and microbodies in the nitrogen cycle. The job of these little individuals is to be fixers, nitrifiers, and denitrifiers of N.

Nitrogen cycle Process

Viruses and single-celled germs play an important role in the nitrogen cycle. They cause this unit to enter the world of the living, converting atmospheric N, and N2, into usable biological components. This element does not last long in the bodies of living beings.

When the bacteria transform organic nitrogen into atmospheric N2, they capture it by transmuting it into ammonia, and NH3. This is absorbed and used by plants in the production of organic molecules.

These nitrogenous particles go to animals when they consume plants. Already in the body, they are attached to it or deposited and defecated as waste. An example is a urea in urine.

Stages of the Nitrogen cycle

Six progressive complex stages are observed in the nitrogen cycle:

  • Fixation. Plants attract nitrogen from the earth’s atmosphere. This hitch in the cycle allows plants to use nutrients to maintain life.
  • Nitrification. It is the procedure by which the bacteria in the earth oxidize ammonia, forging ammonia. This is corroded by other bacteria, transmuting it into nitrate.
  • Assimilation. Phase in which plants are impregnated with ammonia or nitrate. They start the process of exploiting nitrogen. They change it to nutrients, used quietly by the living beings that devour it.
  • Amonificación. This stage, of special importance, disintegrates organic matter. Once the waste has been degraded, the microorganisms are activated, which change it to simple compounds. By metabolizing them, they release excess nitrogen in the form of ammonia.
  • Immobilization. In this stage, similar to that of the metabolic methods of bacteria in the use of N, organic nitrogen is formed.
  • Denitrification. Here the microorganisms intervene, which will be in charge of de-oxidizing nitrate and ammonium. In this way, they favor their return to the atmosphere, like gas.

Aquarium nitrogen cycle 

This cycle is also typical of marine or aquatic ecosystems. Although it varies a bit, ammonification, nitrification, and devitrification techniques are performed by bacteria and archaea from the sea.

Nitrogen reaches the water by running or creeping, resulting from natural fertilizers or those produced by people. Also through the marine trophic links where terrestrial animals approach the sea.

Whatever the mode of entry of nitrogenous organic substances into the water, they are distributed among the various predators. These organisms leave residues of nitrogenous matter at the base of the ocean, where it is corrupted by micro-bacteria. In this way, the microscopic cycle of nitrifying and de-nitrifying is repeated, and the nitro is released back into space.


The Nitrogen cycle is altered in many ways, either by an excess or by a decrease in the amount of nitrogen.

  • Agricultural alterations. It occurs when enormous use is made of artificial humus, whose main component is nitrogen. 50% of the world’s city consumes this type of merchandise.
  • Denitrification. It occurs when this component returns to the atmosphere, completing the cycle. This step is disrupted by the use of fertilizers. In the same way, due to its exportation to various bodies of water, infecting them and making them less drinkable. The minimum requirement should be 10 mg of nitrate per liter of water.
  • Alteration by agricultural means. It is observed when there is an abundance of nitrogen from the use of agricultural fertilizers. The plants do not collect all the elements provided and the excess goes to the environment. Subsequently, N oxides are created that damage stratospheric ozone, causing acid rains that alter ecosystems.


The problems described above have several effects:

  • That there is a loss of biodiversity.
  • A reduction in air quality.
  • An increase in the gases that create global warming.
  • Because nitrogen is a main component in the formation of smog, it causes dyspnoea diseases such as oppression or asthma.


Nitrogen is of great value in an ecosystem, because bacteria use it to transform it and thus acquire energy for their metabolism. The same transformed into ammonium, NH4 +; or nitrate, NO3-, is taken up by plant roots for metabolic tasks. Inclusion in plants benefits herbivorous animals.

This element passes to carnivores when herbivores are consumed by them. At the end of the life cycles of these varieties, the nitro located in their system is restored to the environment, to start the cycle again.

Organisms that participate in the nitrogen cycle

The cycle would not be carried out properly without the intervention or participation of certain sulfur-producing and transporting organisms, such as:

  • Seabirds: Through their excrement, they supply tons of nitrogen annually to the soils and oceans of the entire planet. The very significant contribution of nutrients to the life cycle.
  • Bacteria: Fixing bacteria: Rhizobium, Nostoc, Pasasponia and Frankia. Nitrifying bacteria: Nitrocystis, Nitrosoma, Nitrobacter, Nitrosococcus, and some fungi. Denitrifying bacteria: Thiosphaera, Paracocus, Rhizobium, Pseudomonas, and Thiobacillus.
  • Plants: They are responsible for capturing the nitrogen deposited in the soil and keeping it in its sap. In this way, it can be used by vegetarian animals.


The cycle of this component is very precious for life. Undoubtedly, animals, plants and even humans are not capable of fixing this component, starting from its gaseous state, N2.

It is considered relevant because it is the main element in the multiple transcendental organic methods for organisms. They are the producers of amino acids, nucleic acids, and proteins. Despite being abundant in the atmosphere, it is restrictive because few organisms assimilate it directly.

A process has also been developed that has reacted atmospheric nitrogen, N2, with hydrogen in the form of a gas. In this way, ammonia is obtained, an artificial fertilizer that has made it possible to increase food production internationally.

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