Nutrient Cycles
- There is a finite supply of nutrients on Earth, which are recycled within natural ecosystems.
- The Nitrogen cycle:
- The Phosphorus cycle:
Microorganisms in Nutrient Cycles
- Microorganism play a vital role in nutrient cycles
Microoragnism | Role |
Mycorrhizae | Certain types of fungi associate with roots of plants to increase the surface area for absorption of water and mineral ions, including phosphate ions. |
Free-Living Nitrogen-Fixing Bacteria | In the soil, they reduce nitrogen gas to ammonia. |
Mutualistic Nitrogen-Fixing Bacteria | Use nitrogen gas to produce amino acids |
Saprobiontic organisms | Break down dead organism to release phosphate, ammonia or ammonium compounds |
Nitrifying bacteria | Free living in soil, oxidise ammonium ions into nitrites and nitrites into nitrates |
Anaerobic denitrifying bacteria | Use nitrates in respiration to produce nitrogen gas |
The Use of Fertilisers
- Fertilisers can be used to provide plants with minerals, particularly nitrates, to support their growth
- In agriculture systems, the harvesting of crops prevents the reintroduction of minerals to the soil
- Natural ferilisers consist of dead and decaying remains of plants, animals and their waste
- Artificial fertilisers are mined from rocks before being converted into different forms with their composition tailored for specific crops.
Effects of using fertilisers | Description |
Reduced species diversity | Nitrogen-rich soils favour rapidly growing species |
Leaching (pollutes waterways) | Rainwater dissolves soluble nutrients (e.g. nitrates) and carries them deep into the soil and into waterways such as streams, rivers and lakes. |
Eutrophication | Nitrate levels increase in rivers and lakes due to leaching. The increased plant growth blocks light reaching the water underneath the surface, killing plants at a lower depth. The population of saprobiontic bacteria increase, respiring and reducing oxygen levels, killing other aerobic organisms like fish. |
- Europhication
