Nitrogen is constantly being cycled, just like carbon and water
Nitrogen Cycle
1. Nitrogen in the atmosphere is 78% nitrogen gas
2. Nitrogen gas is turned into mineral ions like nitrates that plants can use
3. Plants take up nitrogen ions and incorporate them into proteins
4. Decomposers break down proteins and return nitrogen to the soil
5. Nitrogen fixation turns atmospheric nitrogen into nitrogen-containing ions in the soil
Types of bacteria in the nitrogen cycle
Decomposers
Nitrifying bacteria
Nitrogen-fixing bacteria
Denitrifying bacteria
Decomposers
Decompose proteins and urea and turn them into ammonia
Nitrifying bacteria
Turn ammonia into nitrites and then into nitrates
Nitrogen-fixing bacteria
Turn atmospheric nitrogen into nitrogen-containing ions in the soil
Denitrifying bacteria
Turn nitrates back into nitrogen gas
Some nitrogen-fixing bacteria live in the soil, others live in nodules on the roots of legume plants
When legume plants decompose, the nitrogen stored in them and their nodules is returned to the soil
Nitrogen-containing ions can also leak out of the nodules during plant growth
Mutualistic relationship
Between legume plants and nitrogen-fixing bacteria - the bacteria get food (sugar) from the plant, and the plant gets nitrogen-containing ions from the bacteria to make into proteins
Crops take up nitrates from the soil as they grow, but when harvested the nitrogen they contain isn't returned to the soil, leading to depletion over time
