PHOSPHORUS CYCLE

Phosphorous Cycle:

• The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.
• Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on earth.
• The production of phosphine gas occurs only in specialized, local conditions.
• Phosphorous is a chemical element found on Earth in numerous compound forms, such as the phosphate ion (PO₄^3-), located in water, soil and sediments.
• The quantities of phosphorus in soil are generally small, and this often limits plant growth.
• That is why people often apply phosphate fertilisers on farmland. Animals absorb phosphates by eating plants or plant-eating animals.

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.

Key steps of the phosphorus cycle:

• Over time, rain and weathering cause rocks to release phosphate ions and other minerals. This inorganic phosphate is then distributed in soils and water.
• Plants take up inorganic phosphate from the soil. The plants may then be consumed by animals. Once in the plant or animal, the phosphate is incorporated into organic molecules such as DNA. When the plant or animal dies, it decays, and the organic phosphate is returned to the soil.
• Within the soil, organic forms of phosphate can be made available to plants by bacteria that break down organic matter to inorganic forms of phosphorus. This process is known as mineralisation.
• Phosphorus in soil can end up in waterways and eventually oceans. Once there, it can be incorporated into sediments over time.

Figure: Phosphorus Cycle

Role of Microorganisms in Phosphorous Cycle:

• The residues of animal, man, plants, birds, etc. contain several phosphates. When they reach the soil, they are acted upon by several microorganisms.
• These organisms break down the P-containing compounds, with the liberation of minerals elements, such as Ca, Fe, Na and this process is known as mineralization.
• Sometimes, the bacteria remove soluble phosphates in soil and use them for cell synthesis. On the death of the bacteria, the phosphate is made available for plants.
• The activity of microorganisms in phosphate solubilization is influenced by various soil factors such as pH, moisture, and aeration.
• Many fungi and bacteria (e.g. Aspergillus, Penicillium, Bacillus etc.) are potential solubilizers of bound phosphates.
• These organisms produce organic acids like citric, glutamic, succinic, oxalic, maleic, fumaric etc. which are responsible for solubilization of insoluble forms of phosphorous.
• These organisms have a role in completing the phosphorous cycle in nature.