Phosphorus Cycle: Definition, Steps, and Human Impact

The phosphorus cycle is a biogeochemical cycle. It is a movement of phosphorus in the form of different chemicals by biosphere, hydrosphere, and lithosphere. The phosphorus cycle is made up of a variety of chemical, biological, and microbiological processes, all of which take place over a long period. The cycle consists of processes such as weathering that take centuries to complete; therefore, the phosphorus cycle is considered to be one of the slowest biogeochemical cycles.

Keyterms: Phosphorus, Phosphorous cycle, Earth, Atmosphere, Biosphere, Biogeochemical cycle, Living organisms, Plants, Animals

Read More: Decomposition

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Definition of Phosphorus Cycle

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The phosphorus cycle is a biochemical process that transports phosphorus from its source to rocks through a variety of organisms into living organisms. Phosphorus moves between the biosphere to maintain balance in its concentration. However, a large amount of phosphorus is present in the lithosphere, where it is present in rocks and sedimentary particles. The phosphorus cycle is considered to be a closed system because the transfer of phosphorus between the biosphere and the soil is much greater than the gain and loss in the whole system.

• Phosphorus is an important nutrient for living things.
• It is an essential component of nucleic acids, such as DNA and phospholipids that form the cell membrane.
• Like calcium phosphate, it also forms the supporting components of our bones.
• Many animals also need large quantities of phosphorus to make shells, bones, and teeth. 
• A natural phosphorus reservoir is a rock, which contains phosphorus in the form of phosphates.
• When rocks are put together, small amounts of these phosphates dissolve in soil solution and are absorbed by the roots of plants (Shown below). 
• Herbivores and other animals get this phosphorus from the plants.
• Trash and dead organisms rot by bacterial-solubilizing phosphate releases phosphorus.
• Unlike the carbon cycle, there is no respiratory release of phosphorus into the atmosphere.

• As phosphorus is a highly effective compound, it is most commonly found in a combination of other substances.

Therefore, acid-producing microorganisms are essential for the production of soluble phosphate from unmixed chemicals. The filtration of phosphorus in various reservoirs changes over time with the phosphorus in the ground running into the sea and phosphorus in the sea, which has led to intoxication. 

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Steps of Phosphorus Cycle

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There are four steps in the phosphorus cycle:

1. Weathering 

The rocks are one of the main sources and reserves of phosphorus, where they remain in contact with other nutrients. Then, the phosphorus reaches the soil by the action of rain, or by acid produced by different microorganisms. Various microorganisms such as actinomycetes, pseudomonas, bacillus, aspergillus, penicillium, etc. are involved in the formation of phosphorus in the soil. In addition, rainfall also causes the dissolution of inanimate phosphorus to be released into the oceans. Natural processes such as volcanic activity and asteroid activity also help to extract phosphorus from the soil.

2. Absorption by plants

Phosphorus is found in the soil and is absorbed by various living organisms such as plants and microorganisms. The amount of phosphorus found in soil plants is very small. Therefore, a phosphorus-containing fertilizer should be added to improve plant growth and soil fertility.

• Marine plants also absorb phosphorus from the lower parts of aquatic life.
• However, certain phosphorus salts may not dissolve in water well, so phosphorus content in water can also be limited.
• Plants can absorb phosphorus directly from the soil, or phosphorus can be made available to plants by various symbiotic microorganisms.

3. Absorption by animals

Plant-absorbed phosphorus is used to create various natural compounds for producers. Organic compounds then move through the food chain as animals feed on the plants, leading to the movement of phosphorus from one species to another. This organic phosphorus also changes as it passes through animals. The phosphorus consumed by animals is used in the production of biomolecule-like nucleotides and connective tissue-like bones. 

4. Decomposition

Organic phosphorus can be recycled into the lithosphere pond by the action of bacterial decay on dead plants and animals. In this process, living phosphorus species are transformed into their unusual forms by the process of mineralization. Various decaying or saprophytic microorganisms such as fungi and bacteria are involved in this measure of phosphorus concentration in the ecosystem. Ground phosphorus is also carried into the sea during the rainy season or when soil evaporates into water bodies. Phosphorus in the sea continues to be absorbed, forming layers of organisms that will lead to the rock formation and the cycle will continue.

Read More: Fragmentation

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Difference Between Phosphorus Cycle and Carbon Cycle

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There are some differences between phosphorous cycle and carbon cycle.

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Human Impact on the Phosphorus Cycle

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Humans activities, such as mining, use of artificial fertilisers, soil run off impact the phosphorus cycle in the following manner:

• Addition of phosphorus in the form of fertilisers to the soil affects the cycle.
• Commercial activities such as mining of phosphate rich rocks reduces phosphorus levels in certain ecosystems.
• Phosphorus rich soil run off in oceans leads to algal blooms, which in turn leads to fall in the oxygen availability of oceans.

Read More: Tundra Ecosystem

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Things to Remember

• Phosphorus cycle is a biochemical process where phosphorous moves into different spheres of the ecosystem.
• Phosphorus cycle is considered to be a closed system.
• The largest source of phosphorus on the Earth is present in the lithosphere, which is composed of oceanic soil and freshwater. 
• The terrestrial biosphere and the sea phosphorus also play an important role in the phosphorus cycle.
• Phosphorus is one of the major components of nucleic acid, biological membranes, and cellular energy transfer systems.
• Phosphorus is also one of the rarest elements in nature that makes it one of the finest inventions.
• Phosphorous cycle is one of the slowest biogeochemical cycle.
• Phosphorus cycle is important as it serve as an essential component of plant nutrient.

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Previous Year Questions

1. Upper part of sea/aquatic ecosystem contains...[NEET 1988]
2. Vertical distribution of different species occupying different...[NEET 2015]
3. What is true of ecosystem?...[NEET 1988]
4. Which ecosystem has the maximum biomass ?...[NEET 2017]
5. Which of the following aquatic plant does not show pollination by water? … (KCET 2021)
6. Aquatic reptiles are … (NEET 1999)
7. Upper part of sea/aquatic ecosystem contains … (NEET 1988)
8. An ecosystem which can be easily damaged but can recover … (NEET 2004)
9. Energy transfer from one trophic level to other...[NEET 1999]
10. An ecosystem which can be easily damaged but can….[NEET 2004]
11. The biomass available for consumption by the herbivores...[NEET 2010]
12. Both hydrarch and xerarch successions lead to...[NEET 2011]
13. During ecological succession...[NEET 2015]
14. In a biotic community, the primary consumers are...[NEET 1995]
15. In an ecosystem, which one shows one-way passage...[NEET 1988]
16. Trichoderma species are potentially useful as….[DPMT 2010]
17. Full name of professor Misra, who is known as the Father of Ecology in India is​...[AMUEEE 2013]
18. In a lake phytoplankton grow in abundance in….​[JKCET 2015]
19. In an ecosystem, the cycling of nutrients is known as...[AMUEEE 2010]
20. In ecological succession, the climax community is best recognized by the following state....[AMUEEE 2010]