Phosphorus Cycle

Phosphorus Cycle

The element phosphorus (P) is an essential macro element in all living organisms. They are found in nucleic acids and phosphate esters. It is an essential component of ATP and other high energy phosphates and phospholipids.

Reservoirs of Phosphorus

1. Phosphate rock like apatite, a large inert reservoir

2. Marine and aquatic sediments

3. Dissolved phosphates in soils and waters

4. Organic phosphates in dead and living organisms.

Phosphorous transformations mostly happen as inter conversion of inorganic to organic phosphate and insoluble form to soluble phosphates.

Phosphate solubilizations

Most of phosphates occur in combination with Calcium, Iron, Magnesium and Aluminium (inorganic P) and thus are insoluble and unavailable to plants and micro organisms. Some micro organisms solubilize those insoluble phosphates by producing organic acids. Example: Thiobacillus, Bacillus thus enabling the plants to utilize it.

Phosphate assimilation

Plants and micro organisms can readily assimilate soluble forms of inorganic phosphates like H₂PO₄^-, HPO₄^-2 and HPO₄^-3 and incorporate them as organic forms of phosphates like ATP, nucleic acids.

Phosphate mineralisation

Breakdown of organic phosphates to form soluble inorganic phosphates is called mineralisation. Organisms produce phosphatase enzymes and catalyse mineralisation. The mineralised phosphates can be utilized by plants (Figure 11.5).