The stages of the nitrogen cycle
1. Nitrogen-fixation
Legume plants such as peas, beans and clover contain nitrogen-fixing bacteria. These bacteria live in swellings in the plant roots called noduleA small swelling on the roots of plants such as peas, beans and clover that contains nitrogen-fixing bacteria.. Nitrogen-fixing bacteria convert nitrogen gas from air into a form that plants can use to make proteins.
Free-living nitrogen-fixing bacteria are also found in the soil. When they die the nitrogen they have fixed into their biomass is converted into ammoniumA nitrogen-containing waste product formed by the decomposition of protein by bacteria..
2. Feeding
Animals consume plant protein, digest it using specific enzymes and absorb the free amino acids.
3. Production of nitrogenous waste products
Animals cannot store excess protein in their bodies. They break it down and turn it into waste products and excrete them from their bodies.
4. Decomposition
decomposerAn organism which eats dead organisms, fallen leaves, animal droppings, etc, and breaks them down into simpler materials. (some free-living bacteria and fungiNon-green plants that obtain their energy by decomposing dead organic remains.) break down animal and plant proteins (from dead organisms) and nitrogenous waste products to release energy. As a result of decompositionThe process of breaking down material to release nutrients back into the soil. nitrogen is released into the soil in the form of ammonium.
5. Nitrification
A group of free-living soil bacteria called nitrifying bacteriaThe bacteria that produce nitrate which is released into soil. convert ammonium into nitrates in order to obtain energy.
6. Uptake of nitrates
Non-legume plants absorb nitrates from the soil into their roots and use the nitrates to produce their proteins.
7. Denitrification
This is when bacteria in the soil convert the nitrate back into nitrogen gas which then gets released back into the atmosphere.