Phosphorus is an essential mineral nutrient for all plants and animals. Phosphorus forms the ions the of phosphates and hydrogen phosphates. These phosphates are important parts of DNA molecules and are also a part of energy storing molecules like the ATP and ADP and also fat molecules of the cell membranes. Phosphorus is also a building block of certain parts like bones and teeth in humans and animals.
Phosphorus is found in water, soil and sediments, it cannot be found in air in the gaseous state like other compounds of matter cycles. It is found mainly cycling through soil, sediments and water. The phosphorus cycle is the slowest of the biogeochemical cycles. Phosphorus enters the environment from rocks and from deposits. Phosphate rock is commercially known as apatite and other deposits from the fossilized bone or bird droppings. Weathering of rocks releases phosphorus as ions which are soluble in water. Terrestrial plants need phosphate as fertilizers in the form of nutrients.
The phosphorus cycle is defined as the biogeochemical cycle which describes the movement of phosphorus through the spheres of the ecosystem that is through lithosphere, hydrosphere and biosphere. Atmosphere does not have an important role in the phosphorus cycle as phosphorus and phosphorus based compounds are usually in solid form in typical temperature range.
The phosphorus cycle process is as follows:
- The phosphorus enters the soil and water through the weathering of rocks.
- Plants take in these phosphorus ions from the soil.
- The phosphates are then transferred from plants to herbivores animals.
- These herbivores animals are eaten by carnivores.
- The phosphates that are absorbed by the animals are returned to the soil through excretion and from decomposition of plants and dead material by microbes.
- The dead plant materials and other waste products are decayed through the action of bacteria.
- The phosphate is released out to the environment by this process.
- The phosphate in the soil is leached out or eroded into water.
- The water is again utilized by algae and plants as nutrients.
The lack of phosphate results in slow growing or stunted plant growth. If there is more of phosphate in the plant, there is excess growth seen in the some algae.
- Human impacts on the phosphorus cycle are from the introduction of synthetic fertilizers.
- Plants may not be able to use the phosphate in the form of fertilizers; most of the nutrients is lost through water run-off.
- The phosphate present in the water sediments at bottom of water body.
- Manure when applied to the frozen ground most of it will be lost during the spring thaw.
- In certain large feed application, it may result in excessive run-off of phosphate into streams.
- Other source of phosphates due to human activity is the out flow from sewage plants.
- The phosphate from the sewage is not removed, if it is not treated and extra amount of phosphate enters the water body.
High concentration of phosphate in water system can lead to eutrophication of fresh and inshore marine waters, which leads to algal blooms.
Let us understand, why is phosphorus cycle important. The following statements describe the importance of phosphorus cycle.
- Plants and animals require phosphorus as an essential nutrient, but it is a limiting nutrient for aquatic organisms.
- Some of the important life sustaining molecules is composed of phosphorus.
- Most of the phosphorus that is mined is used to make fertilizers.
- Weathering of rocks and minerals releases phosphorus to the environment which is taken up by plants and is processed into organic compounds.
- Phosphate is biologically important as it is a component of nucleotides and nucleic acids like DNA and RNA.
- It is also a part of energy storage molecules like ATP, ADP, GDP, etc.
- The double helical form of the DNA is possible only because the phosphate molecules forms a phosphate ester bridge that binds the double helix.
- Phosphorus is found in bones in the form of calcium phosphate.
- It is also present in the enamel of teeth of mammals, in the exoskeleton of insects.
- It is also present in the form of phospholipids which is found in all biological membranes.
- Phosphorus also functions in maintaining the acid base homeostasis in the human body acting as a buffering agent.
- It is also essential for metabolic reactions to release energy.
- It is also required to encode information on genes.
The following is the illustration of phosphorus cycle: