The Phosphorus Cycle

Phosphorus is a chemical element used by all living creatures primarily in the creation of energy molecules. Phosphorous is largely unavailable to organisms and is mostly stored in marine sediments and terrestrial soils, which over time form sedimentary rock.

Almost all the phosphorus used by terrestrial organisms is derived from the weathering of these sedimentary rocks; moving phosphorus into the soil where plants can uptake it, and therefore entering the ecosystem. However, only a small fraction of this phosphorous can actually be used by organisms, and so much of it is transferred to the oceans and deposited as marine sediments again forming  sedimentary rock. This rock then re-enters the cycle after millions of years of tectonic uplift raising it above sea level where it undergoes weathering.

Due to phosphorus being largely unavailable to organisms and consequently a limiting factor to growth, some plants have formed a symbiotic relationship known as mycorrhiza with fungi, wherein plants provide the fungi with energy in return for nutrients such as phosphorus and nitrogen.

Due to the mining of phosphorus rich rock deposits, and increased organic waste and industrial discharge, the availability of phosphorus in ecosystems has increased; leading to eutrophication in freshwater systems.

Figure 1- a visual representation of the phosphorus cycleNWK Phosp cycle.png

“Untitled”, 2013, Wikimedia Commons, source: (accessed 5/12/18)


Key Terms

Organism – An individual plant, animal or cell.

Marine – Referring to, or found in the sea.

Terrestrial – Referring to, or found on land.

Sedimentary rock – One of the three main rock types formed by the consolidation of sediments.

Weathering – The breaking down of surface rocks due to environmental conditions.

Ecosystem – A biological system of interacting plants, animals and cells, and the physical environment in which they are contained.

Tectonic uplift – The raising of an area as a result of processes occurring within the Earth.

Mycorrhiza – A symbiotic relationship between some plants and fungi that provides the plants with nutrients and the fungi with energy.

Eutrophication – The excessive richness of nutrients in a water body causing a damagingly dense growth of plant life.







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