The
phosphorus cycle is the
biogeochemical cycleIn ecology and Earth science, a biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth...
that describes the movement of
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
through the
lithosphereThe lithosphere is the rigid outermost shell of a rocky planet.- Earth's lithosphere :...
,
hydrosphereA hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet....
, and
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
. Unlike many other biogeochemical cycles, the
atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.
Phosphorus is an essential nutrient for plants and animals in the form of ions.
The
phosphorus cycle is the
biogeochemical cycleIn ecology and Earth science, a biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth...
that describes the movement of
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
through the
lithosphereThe lithosphere is the rigid outermost shell of a rocky planet.- Earth's lithosphere :...
,
hydrosphereA hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet....
, and
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements...
. Unlike many other biogeochemical cycles, the
atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.
Phosphorus in the environment
Phosphorus is an essential nutrient for plants and animals in the form of ions. Phosphorus forms parts of important life sustaining molecules but is not very common in the biosphere. Phosphorus does not enter the atmosphere, remaining mostly on land and in rock and soil minerals. 80 percent of the phosphorus is used to make fertilizers and a type of phosphorus such as dilute phosphoric acid is used in soft drinks. Phosphates may be effective in such ways but they also cause pollution problems in lakes and streams. Over enrichment of phosphate can lead to algae bloom, because of the excess of nutrients. This causes more algae to grow, bacteria consumes the algae and causes more bacteria to increase in numbers. They use all the oxygen in the water during cellular respiration, causing many fish to die.
Phosphorus normally occurs in nature as part of a
phosphateA phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
ion, consisting of a phosphorus
atom and some number of oxygen atoms, the most abundant form (called orthophosphate). Most phosphates are found as salts in ocean
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
s or in rocks. Over time, geologic processes can bring ocean sediments to land, and
weatheringWeathering is the decomposition of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice,...
will carry these phosphates to terrestrial habitats.
PlantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s absorb phosphates from the soil, then bind the phosphate into organic compounds. The plants may then be consumed by
herbivoreA herbivore is an animal that is adapted to eat plants and not meat.Herbivory is a form of predation in which an organism consumes principally autotrophs such as plants, algae and photosynthesizing bacteria....
s who in turn may be consumed by
carnivoreA carnivore , meaning 'meat eater' , is an animal that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of vertebrate and/or invertebrate animal tissue, whether through predation or scavenging...
s. After death, the animal or plant decays, and the phosphates are returned to the soil. Runoff may carry them back to the
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
or they may be reincorporated into rock.
The primary biological importance of phosphates is as a component of
nucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides play central roles in metabolism...
s, which
serve as energy storage within cells (
ATPAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
) or when linked together, form the nucleic acids
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
and
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
. Phosphorus is also found in bones, whose strength is derived from
calcium phosphateCalcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions.It is the principal form of calcium found in bovine milk...
, and in
phospholipidPhospholipids are a class of lipids and are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from...
s (found in all
biological membraneA biological membrane or biomembrane is an enclosing or separating amphipathic layer that acts as a barrier within or around a cell. It is almost invariably a lipid bilayer, composed of a double layer of lipid molecules and proteins that may constitute close to 50% of membrane...
s).
Phosphates move quickly through plants and animals; however, the processes that move them
through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest
biogeochemical cycles.
Unlike other cycles of matter compounds, phosphorus cannot be found in air as a gas. This is because at normal temperature and circumstances, it is a solid in the form of red and white phosphorus. It usually cycles through water, soil and sediments. Phosphorus is typically the limiting nutrient found in streams, lakes and fresh water environments. As rocks and sediments gradually wear down, phosphate is released. In the atmosphere phosphorus is mainly small dust particles.
Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by leaching through the action of rain are balanced in the gains from weathering rocks. In soil, phosphate is absorbed on clay surfaces and organic matter particles and becomes incorporated (immobilized). Plants dissolve ionized forms of phosphate. Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores. Herbivores and carnivores excrete phosphorus as a waste product in urine and feces. Phosphorus is released back to the soil when plants or animal matter decomposes and the cycle repeats.
Human interference
Human interference in the phosphorus cycle occurs by overuse or careless use of phosphorus fertilizers. This results in increased amounts of phosphorus as pollutants in bodies of water resulting in
eutrophicationEutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem...
.