PHOSPHORUS CYCLE

• Phosphorus is needed to make phosphate (PO43-)
• Phosphate is needed to make DNA, ATP, phospholipids, etc
• Plants take up phosphate via their root hairs by active transport
• Phosphate is distributed through the food web
• Saprobionts decompose DNA in dead material, releasing phosphate into the soil
• Some phosphate is "leached" in solution into water bodies
• Phosphate is used in aquatic food webs, and dead material sinks
• Phosphate ultimately ends up in marine sediments, which turn into sedimentary rock at the bottom of the ocean
• When uplifted to the surface, these rocks weather down to release phosphate
• Mycorrhizae help to facilitate the uptake of water and inorganic ions by plants
• • A mycorrhiza is an association between a fungus and a plant root.
  • Plural: mycorrhizae.
  • The fungus acts as an extension to the root system, massively increasing the surface area for water and inorganic ion uptake for the plant.
  • This is especially important for phosphate, which is a major limiting factor in plant growth due to the slower nature of the phosphorus cycle.
  • In return, the plant shares some of its carbohydrate with the fungus for respiration: a “mutualistic” relationship where both species benefit.
• • In a natural ecosystem, nutrients can be recycled by saprobiotic decomposition of dead material.
  • On a farm, crops are harvested and livestock are sent for slaughter. This removes nutrients from the area.
  • Fertiliser can be applied to the field to replenish the lost nutrients.
• • Natural “organic” fertilisers include manure (animal faeces). Organic fertilisers have the nitrogen and phosphorus locked up in carbon-containing compounds (organic means carbon-containing).
• Inorganic nitrate and phosphate fertiliser can also be manufactured artificially
• • Fertilisers increase plant growth by, for example, providing more nitrate for making protein and more phosphate for making DNA.