1. Nitrogen Fixation: This is the conversion of atmospheric nitrogen gas (N2), which is unusable by most organisms, into a usable form. This is primarily done by nitrogen-fixing bacteria, found in soil and aquatic environments. They convert N2 into ammonia (NH3).
2. Nitrification: Ammonia is further converted into nitrite (NO2-) and then nitrate (NO3-) by nitrifying bacteria. Nitrate is the form of nitrogen most readily used by plants.
3. Assimilation: Plants absorb nitrate from the soil and use it to build proteins and nucleic acids (DNA and RNA). Animals then obtain nitrogen by consuming plants or other animals.
4. Ammonification: When organisms die, decomposers (bacteria and fungi) break down their organic matter and release nitrogen back into the soil as ammonia (NH3).
5. Denitrification: Under anaerobic conditions (without oxygen), denitrifying bacteria convert nitrate back into nitrogen gas (N2), which is released into the atmosphere. This completes the cycle.
6. Industrial Nitrogen Fixation: Human activities, such as the production of fertilizers and burning fossil fuels, add significant amounts of nitrogen to the environment. These activities can lead to increased nitrogen pollution in water and air.
These six steps form a continuous cycle, ensuring that nitrogen is constantly moving through the environment, available for life, and regulated.
