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Nitrogen Cycle

Last updated: August 12, 2018

What Does Nitrogen Cycle Mean?

The nitrogen cycle is the most important nutrient cycle in our ecosystem. It is the process in which nitrogen is transformed to its various chemical forms through biological and physical processes. All living organisms use nitrogen to produce organic substances including amino acids, proteins and nucleic acids that are vital for metabolism, growth, reproduction and the life cycle. It is the primary nutrient, essential for the survival of all living organisms. Plants obtain nitrogen as inorganic nitrate from the soil solution. Animals receive the required nitrogen by consuming organic matter containing nitrogen.

Safeopedia Explains Nitrogen Cycle

Nitrogen go through different transformations in the ecosystem. Nitrogen cycle is the key to productivity in the biosphere and it is highly influenced by the activities of a diverse accumulation of microorganisms, such as bacteria and fungi. Major transformations and stages of nitrogen cycle are outlined below:

  • Fixation - Nitrogen gas in the atmosphere is transformed to nitrate by nitrogen-fixing bacteria in soil or root nodules or lightning. The Haber process converts nitrogen gas into ammonia used in fertilizers
  • Nitrification – Ammonia is converted to nitrates by nitrifying bacteria in the soil. It is the process that converts ammonia to nitrite and then to nitrate
  • Assimilation - Plants absorb nitrates from the soil and use these to build up proteins. The plant may be eaten by an animal, and its biomass used to produce animal protein
  • Ammonification - Decomposers break down the bodies of dead animals and organisms resulting in nitrogen being returned to the soil as ammonia. Urea and ingested material is broken down by decomposers
  • De-nitrification - Denitrifying bacteria in the soil break down nitrates and return nitrogen back to the air

Human activities like fuel burning, use of fertilizers have an impact on the nitrogen cycle. These increase the amount of biologically available nitrogen in an ecosystem. Large changes in the amount of nitrogen can affect the nitrogen cycle in ecosystems. The additional nitrogen may lead to nutrient imbalance in plants and, subsequently, changes in biodiversity, carbon storage, etc.. Uncontrolled use of fertilizers in the form of nitrate may ultimately mix into drinking water causing danger to human health. Alterations to the nitrogen cycle may lead to an increased risk of parasitic and infectious diseases among humans and wildlife and increased acidification in freshwater ecosystems.


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