Cycle of nitrogen
The nitrogen is the most abundant element in the atmosphere (78%), where N is as N2, although most of living beings can not be used directly. Only some bacteria, fixed to the roots of some plants, are capable of fixing nitrogen so that it can be used by plants and introduce it into the trophic chain.
The nitrogen cycle can be summarized in the following steps:
- The nitrogen fixing bacteria aspirated soil use nitrogen to create nitrates that plants can absorb through their roots and synthesize their own proteins.
- Herbivores, and later carnivores, will get the necessary nitrogen through their diet. With this nitrogen they will be able to create their own proteins and nucleic acids.
- The decomposing microorganisms transform the nitrogenous substances originated in the excretion of living beings, such as urea, and the remains of dead organisms, so that they can be used again by plants.
- The nitrifying bacteria convert ammonium produced by microorganisms decomposers in plants absorb nitrates. The denitrifying bacteria transformed part of these nitrates in nitrogen which is returned to the atmosphere.
Nitrogen is a limiting factor for plant development, since its scarcity causes problems in plant development. Excess fertilizers or fertilizers used in agriculture can cause eutrophication of lakes and rivers.