Nitrogen fixation and Nitrification
- Atmospheric nitrogen cannot be used directly by plants and animals.
- Nitrogen fixation occurs when lightning strikes or through the Haber process.
- Nitrogen-fixing bacteria such as Rhizobium live inside the root nodules of leguminous plants such as beans peas and clover.
- Rhizobium converts atmospheric nitrogen into ammonia which the plant can use as its fixed nitrogen source. They have a mutualistic relationship.
- Nitrifying/chemoautotrophic bacteria oxidise ammonium ions to nitrites (Nitrosomonas) and oxidise nitrites into nitrates (Nitrobacter).
- Plants take the nitrates in through their roots from the soil and use them to make amino acids and proteins.
- Animals can then eat the plants to get proteins.
Decomposition and Denitrification
- Process where ammonium ions are produced from ammonium containing compouds such as urea.
- Dead plant and animal waste contains nitrogenous waste.
- Over time, these wastes decay and ammonia is released.
- Nitrifying bacteria convert the ammonia to nitrates.
- Some of the nitrates are taken up by the plants and used again (nitrification).
- Some of the nitrates go through the process denitrification.
- Denitrifying bacteria convert the nitrates back into atmospheric nitrogen which goes back to the atmosphere.
Nitrogen fixation = Nitrogen gas --> Ammonia (Nitrogen-fixing bacteria e.g. Rhizobium)
Nitrification = Ammonia --> Nitrites --> Nitrates (Nitrifying bacteria - Nitrosomonas/Nitrobacter)
Ammonification/Decomposition = Decay and produce ammonia (-->Nitrification/Denitrification)
Denitrification = Nitrates -> Atmospheric nitrogen (Denitrifying bacteria)