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What is the Natural Nitrogen Cycle?

What is the Natural Nitrogen Cycle?

Nitrogen is found in every living organism, be it a bacterium, plant, fungus or animal, as it is found in proteins, amino acids and DNA as an important building material. Since the cells must be renewed regularly, they must accordingly be re-supplied with necessary substances such as nitrogen.

The natural nitrogen cycle:

  • Ammonification
  • Nitrification
  • Nitrogen assimilation
  • Denitrification
  • Nitrogen fixation
  • Nitrification

The Ammonification

The nitrogen cycle "starts" with the ammonification. In this process, the nitrogen, which is contained in all compounds in organic matter, released by destructors such as bacteria and fungi. These destructors decompose the organic parts and thus gain energy. However, amonification can not only be effected by destructors but also by other chemical processes such as e.g. the hydrolysis of urine.

Ammonia makes nitrogen available again in the form of NH3 or NH4 + to the ecosystem.

The Nitrification

Nitrification is a two-step process involving two groups of bacteria, nitrite bacteria and nitrate bacteria. The two groups of bacteria are interdependent because ammonia must first be converted into nitrite and then into nitrate.

The first step is through the nitrite bacteria. These oxidize ammonia with molecular oxygen to nitrite to gain energy from this process.

NH3 + 1,5 O2 → NO2- + H2O

For the next step, nitrate bacteria such as the Nitrobacter are necessary because nitrite is converted into nitrate by oxidation.

NO2- + 0.5 O2 → NO3-

Nitrogen Assimilatio

Nitrate and ammonia are inorganic compounds and are taken up by plants and other organisms to produce nitrogen-containing organic compounds, e.g. Amino and nucleic acids or proteins to form.

On plants both ammonia and nitrate fertilizes and stimulates growth.

Many plants store more nitrate than they need, which is why it can be health-threatening to warm up nitrate-storing vegetables such as chard or spinach more than once. In artificial nitrification by heat, e.g. nitrite is formed in the cooking pot, which can be poisonous especially for children.

The excretions and remnants of microorganisms, plants, fungi and animals also contain nitrogen. This is either converted to ammonia by ammonification or released by other chemical processes.


Various anaerobic bacteria can use nitrate or nitrite for oxidation and thus gain energy for themselves. In this process, nitrate or nitrite N2 is released in several intermediate steps, which largely escapes into the atmosphere.

Nitrogen Fixation

Very few living things are able to bind nitrogen in its original form and thus make it accessible to plants and microorganisms. The rare species include cyanobacteria, bacteria of the genus Frankia and various other bacteria such as the nodule bacteria.

These usually live in symbiosis with plants, where they benefit from the mass transfer.

Nitrification by Energy

Nitrogen, which occurs in the atmosphere, is bound to nitrate during a thunderstorm.