Phosphorus Cycle

• Plants and animals need phosphorus to make biological molecules, such as phospholipids, DNA and ATP. Phosphorus is found in rocks and dissolved in oceans in the form of phosphate ions. Phosphate ions dissolved in water in the soil can be assimilated by plants and other producers. The phosphorus cycle shows how phosphorus is passed through the ecosystem.
• PC P1:

  • Phosphate ions in rocks are released into the soil by weathering.
  • Phosphate ions are taken into the plants through the roots. Mycorrhizae greatly increases the rate at which phosphorus can be assimilated.
  • Phosphate ions are transferred through the food chain.
• PC P2:

  • Phosphate ions are lost from the animals in waste products.
  • When plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. These microorganisms also release the phosphate ions from urine and faeces.
• PC P3:

  • Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, such as algae, and passed along the food chain to birds.
  • The waste produced by sea birds is known as guano and contain a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils. It is often used as a natural fertiliser.