the three steps of the nitrogen cycle in order, starting with nitrogen gas in the atmosphere are
1. Nitrogen Fixation: This step involves the conversion of nitrogen gas (N2) from the atmosphere into a usable form by certain types of bacteria. These bacteria, known as nitrogen-fixing bacteria, can be free-living or symbiotic with plants. Nitrogen fixation can occur through biological or industrial processes, such as lightning or Haber-Bosch process.
2. Nitrification: In this step, the usable form of nitrogen, which is now ammonia (NH3) or ammonium (NH4+), is converted by nitrifying bacteria into nitrite (NO2-) and then further converted into nitrate (NO3-). It involves two separate reactions: oxidation of ammonia to nitrite and oxidation of nitrite to nitrate. The nitrifying bacteria responsible for this process are Nitrosomonas and Nitrobacter.
3. Denitrification: This step involves the conversion of nitrate (NO3-) back into nitrogen gas (N2), completing the nitrogen cycle. Denitrifying bacteria carry out this process in anaerobic conditions, where oxygen is limited. These bacteria, such as Pseudomonas and Achromobacter, use nitrate as an alternative electron acceptor in respiration. This process releases nitrogen gas back into the atmosphere and starts the cycle anew.