The Nitrogen Cycle
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems.
Important processes in the nitrogen cycle include:
1. fixation,
2. ammonification,
3. nitrification,
4. denitrification.
Nitrogen becomes available to plants through the action of nitrogen-fixing bacteria that change atmospheric nitrogen into nitrates, which are used by the plants for protein synthesis.
Nitrogen fixation is the conversion of N to ammonia (NH ) by several species of aquatic or terrestrial bacteria, either symbiotic with plants or living in the soil.
Ammonification occurs when bacteria convert nitrogen from wastes or decomposition to NH, which again is dissolved to form ammonium.
Nitrification is the process of converting some of the ammonium in the soil into nitrates or nitrites that can then be assimilated by plants or animals. Denitrification occurs when other bacteria convert nitrates back to N, which is then released into the atmosphere.
Most of the air you breathe is nitrogen. Essential to living organisms, nitrogen is a critical component of proteins and nucleic acids and is often in short supply. Despite their dependence on nitrogen, very few organisms can make any use of the atmospheric N2 form of nitrogen. They depend on the nitrogen cycle and the role of specific organisms to supply the nitrogen needed. There are several components of the nitrogen cycle, which convert atmospheric nitrogen to a usable form and eventually back to N2.
Nitrogen fixation is the conversion of N2 to ammonia (NH3) by several species of aquatic or terrestrial bacteria, either symbiotic with plants or living in the soil. NH3 can dissolve quickly in water and is converted to ammonium, which is then taken into the tissues of plants, such as soybeans, as well as organisms feeding on these plants in a process called assimilation. Nitrogen is also released through waste products when these organisms die and decompose. Thus, without the essential nitrogen-fixing organisms, modern agriculture often must add sufficient nitrogen to soils for food crops to grow.
Ammonification occurs when bacteria convert nitrogen from wastes or decomposition to NH3, which again is dissolved to form ammonium. Nitrification is the process of converting some of the ammonium in the soil into nitrates or nitrites that can then be assimilated by plants or animals. Denitrification occurs when other bacteria convert nitrates back to N2, which is then released into the atmosphere.