Phosphorus Cycle
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.
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 role of phosphorus in animals and plants
Phosphorus is an essential nutrient for animals and plants. It plays a critical role in cell development and is a key component of molecules that store energy, such as ATP (adenosine triphosphate), DNA and lipids (fats and oils). Insufficient phosphorus in the soil can result in a decreased crop yield.
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
Most phosphorus is unavailable to plants
Since most of our phosphorus is locked up in sediments and rocks, it’s not available for plants to use. A lot of the phosphorus in soils is also unavailable to plants.
Soil phosphorus becomes unavailable to plants through several routes:
• Bacteria: Bacteria convert plant-available phosphate into organic forms that are then not available to plants. Although other bacteria make phosphate available by mineralisation, the contribution of this is small.
• Adsorption: Inorganic (and available) phosphorus can be chemically bound (adsorbed) to soil particles, making it unavailable to plants. Desorption is the release of adsorbed phosphorus from its bound state into soil solution.
• pH: Inorganic phosphorus compounds need to be soluble to be taken up by plants. This depends on the acidity (pH) of the soil. If soils are less than pH 4 or greater than pH 8, the phosphorus starts to become tied up with other compounds, making it less available to plants.
Phosphate fertilisers replenish soil phosphorus
Many farmers replenish phosphorus through the use of phosphate fertilisers. The phosphorus is obtained by mining deposits of rock phosphate. Locally produced sulfuric acid is used to convert the insoluble rock phosphate into a more soluble and usable form – a fertiliser product called superphosphate.
Water pollution
Phosphates are effective fertilizers, but they also cause pollution problems in lakes streams. Because phosphorus is often the nutrient in limited supply, even a small increase in availability can cause a significant effect. Over-enrichment of phosphate can lead to algae blooms. This excess of algae causes increased consumption by bacteria, which then leads to even higher bacterial concentrations. In the process the bacteria use up much of the dissolved oxygen in the water during cellular respiration and thereby cause the death of fish due to oxygen deprivation.
Human Impact
• 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.
Interesting Phosphorus Cycle Facts:
• The element phosphorous was discovered in 1669 by Hennig Brand in Germany.
• Once phosphorus gets lost during runoff, it remains lost from the cycle forever.
• Phosphorus is essential for plant growth.
• Phosphorus can most likely be found underground in soil and rocks.
• When too much phosphorus containing fertilizer is washed into the ocean, it causes an increase in algae growth called an algae bloom.
• After rocks break down underground, phosphorus is usually released and absorbed by plants.
• Once an animal or plant dies and decays, phosphorus is returned to the ground.
• Once phosphorus enters a plant or animal, it moves through the organism very quickly.
• Phosphorus is responsible for holding DNA together.
• Animals receive phosphorus directly by eating plants or indirectly by eating plant eating animals.
• If released phosphorus from marine animals becomes part of the underwater sediment, it may remain there forever.