Phosphorus cycle
In animals, inorganic phosphorus in the form of apatite (Ca5(PO4)3(OH,F)) is also a key component of bones, teeth (tooth enamel), etc.
[5] On the land, phosphorus gradually becomes less available to plants over thousands of years, since it is slowly lost in runoff.
In the long-term global cycle, however, the major transfer is driven by tectonic movement over geologic time and weathering of phosphate containing rock such as apatite.
[7] However, as phosphorus enters aquatic ecosystems, it has the possibility to lead to over-production in the form of eutrophication, which can happen in both freshwater and saltwater environments.
Weathering of rocks and minerals release phosphorus in a soluble form where it is taken up by plants, and it is transformed into organic compounds.
The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA.
Besides making biomolecules, phosphorus is also found in bone and the enamel of mammalian teeth, whose strength is derived from calcium phosphate in the form of hydroxyapatite.
[17][18] The global phosphorus cycle includes four major processes: In terrestrial systems, bioavailable P (‘reactive P’) mainly comes from weathering of phosphorus-containing rocks.
The most abundant primary phosphorus-mineral in the crust is apatite, which can be dissolved by natural acids generated by soil microbes and fungi, or by other chemical weathering reactions and physical erosion.
[21][25] Phytoplankton cell lysis releases cellular dissolved inorganic and organic phosphorus to the surrounding environment.
Plant growth depends on the rapid root uptake of phosphorus released from dead organic matter in the biochemical cycle.
Several of those organic acids are capable of forming stable organo-metal complexes with various metal ions found in soil solutions.
The production and release of oxalic acid by mycorrhizal fungi explain their importance in maintaining and supplying phosphorus to plants.
[17][33] The availability of organic phosphorus to support microbial, plant and animal growth depends on the rate of their degradation to generate free phosphate.
Eutrophication is when waters are enriched by nutrients that lead to structural changes to the aquatic ecosystem such as algae bloom, deoxygenation, reduction of fish species.
It does occur naturally, as when lakes age they become more productive due to increases in major limiting reagents such as nitrogen and phosphorus.
[37] Antrhopogenic effects can also cause phosphorus to flow into aquatic ecosystems as seen in drainage water and runoff from fertilized soils on agricultural land.
[38] Additionally, eroded soils, which can be caused by deforestation and urbanization, can lead to more phosphorus and nitrogen being added to these aquatic ecosystems.
[39] These all increase the amount of phosphorus that enters the cycle which has led to excessive nutrient intake in freshwater systems causing dramatic growth in algal populations.
[42] This increase in phosphorus has led to more eutrophication in ocean waters as phytoplankton blooms have caused a drastic shift in anoxic conditions seen in both the Gulf of Mexico[43] and the Baltic Sea.
[45] This could possibly create a self-sustaining cycle of oceanic anoxia where the constant recovery of phosphorus keeps stabilizing the eutrophic growth.
To remove phosphorus continually, it is necessary to add more new soils within the wetland from remnant plant stems, leaves, root debris, and undecomposable parts of dead algae, bacteria, fungi, and invertebrates.
[46][51] Regardless, humans have had a profound impact on the phosphorus cycle with wide-reaching implications about food security, eutrophication, and the overall availability of the nutrient.
[52] Other human processes can have detrimental effects on the phosphorus cycle, such as the repeated application of liquid hog manure in excess to crops.
[53] In poorly drained soils or in areas where snowmelt can cause periodic waterlogging, reducing conditions can be attained in 7–10 days.
