Nitrogen Cycle (Meaning and Explanation)

We explain what the nitrogen cycle is, what its stages are and its importance. Also, how human activity affects this biogeochemical cycle.

What is the nitrogen cycle?

The nitrogen cycle is the circulation of nitrogen on planet Earth. During this cycle, nitrogen is part of different chemical compounds that move between different ecosystems and the environment that surrounds them.

Nitrogen found in the atmosphere in gaseous form (N₂) cannot be used by plants and animals to perform their vital functions. This is why a set of processes is necessary that transform atmospheric nitrogen into nitrogen-containing chemical compounds such as nitrate ions (NO₃^–) and ammonium (NH₄⁺), and that living organisms can use to perform their functions.

In these processes (necessary to convert nitrogen from the atmosphere into useful forms of nitrogen) Microorganisms called bacteria and fungi are involved. These microorganisms are capable of transforming nitrogen from the atmosphere into chemical compounds that can be used by plants and animals.

This cycle ensures that nitrogen moves between living and non-living organisms, and also allows atmospheric nitrogen to be transformed into forms usable by living beings. For example: nitrogen in the form of NH ions₄⁺ and not₃^–It is absorbed by plants through their roots and then incorporated by animals when they consume the plants.

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Characteristics of the nitrogen cycle

The nitrogen cycle involves different stages and occurs relating different layers of the Earth. Some characteristics of the nitrogen cycle are:

During the cycle, nitrogen is part of different chemical compounds that circulate on the planet.
The cycle ensures that nitrogen is available in chemical forms that can be used by living things, such as nitrate (NO₃^–) and ammonium (NH₄⁺).
The stages of the cycle occur mainly in the biosphere, atmosphere and geosphere.

Stages of the nitrogen cycle

In the nitrogen cycle, the different levels of living beings are interrelated, autotrophic organisms (which produce their organic compounds from simple inorganic compounds and do not feed on other organisms) and heterotrophic organisms (which do not produce their organic compounds from from simple inorganic compounds, but rather they feed on plants or animals), the tiny organisms that decompose organic matter (bacteria and fungi), and nitrogen from the atmosphere (N₂).

The nitrogen cycle is made up of several stages:

Fixation Through fixation, atmospheric nitrogen (N₂) is transformed into chemical compounds that contain nitrogen (nitrate (NO₃^–) and ammonium (NH₄⁺)) and that living organisms can use to carry out their vital functions. This process can occur through the oxidation of N₂which occurs due to the action of rays, and by the action of certain microorganisms that convert N₂ in NH₄⁺.

Nitrification Through nitrification, ammonia (NH₃) or the ammonium ion (NH₄⁺) are transformed into chemical compounds that can be assimilated by plants and animals. This process occurs due to the action of certain microorganisms that can transform NH₃ and the NH₄⁺ into nitrite ions (NO₂^–) and nitrates (NO₃^–), which can then be incorporated into plants through their roots and into animals when they eat the plants.

Assimilation Through assimilation, plants and animals incorporate nitrogen into their organisms. Thus, nitrogen returns to the environment when these organisms die and decompose.

Ammonification Through ammonification, the nitrogen present in living beings is released into the environment as part of ammonia (NH₃) or ammonium ion (NH₄⁺). This occurs when dead organisms decompose, since there are microorganisms (bacteria and fungi) that are capable of decomposing dead plants and animals, and as a result of this process they can release nitrogen into the environment. In addition, the nitrogen present in animals can be released into the environment through their waste, such as urine and excrement.
Denitrification Through denitrification some microorganisms (denitrifying bacteria) can decompose nitrate ions (NO₃^–) and nitrite (NO₂^–), releasing gaseous nitrogen (N₂) to the atmosphere.

Importance of the nitrogen cycle

The nitrogen cycle is very important because during its course atmospheric nitrogen (N₂), which is not usable by living beings, is transformed into chemical forms such as nitrates (NOT₃^–), which these beings can use in their organisms.

Impact of human activity on the nitrogen cycle

The development of activities by human beings has increased nitrogen levels on the planet. Although nitrogen is essential for the correct functioning of different ecosystems, Excess nitrogen contributes to climate change and the pollution of the planet's water.

The human activities that add the most nitrogen to the planet are those related to the excessive use of fertilizers in agriculture. In addition, nitrogen is also released during the burning of fossil fuels to generate energy.

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References

Donald E. Canfield, Alexander N. Glazer, Paul G. Falkowski. (2010) “The Evolution and Future of Earth's Nitrogen Cycle” Science vol 330.
Cerón Rincón, LE, & Ancízar Aristizábal Gutiérrez, F. (2012). Dynamics of the nitrogen and phosphorus cycle in soils. Colombian Journal of Biotechnology, 14(1), 285-295.
Avila, JP, Canul, RP, & Sansores, AC (2002). Analysis of the nitrogen cycle in the environment in relation to groundwater and its effect on living beings. Engineering, 6(3), 73-81.