Phosphorus availability in soils
Phosphorus is an essential macroelement with a wide range of structural and regulatory functions. It is often a limiting nutrient in terrestrial ecosystems.
Key Facts:
- P is a building block of nucleic acids (DNA, RNA) & phospholipids in cell membranes
- P plays a key role in energy metabolism (ATP, NADPH)
- Total P concentration in crops ranges from 0.1 to 0.5 %.
Function:
- P plays a role in the light reaction of photosynthesis
- It affects CO2 assimilation rate by the carboxylation of RuBisCo
- ATP and other high-energy P compounds are essential for the active transport of other nutrients
- P deficiency affects the root-to-shoot ratio and changes in root architecture (facilitating uptake of P in the topsoil)
- It is a component of phytin, a major storage form of P in seeds
Availability:
- Plants take up P as the inorganic orthophosphate ions H2PO4 and HPO4, depending on soil pH
- In acidic soils, P is fixed by iron compounds
- In the alkaline pH range, P reacts with calcium and becomes inaccessible for a plant
- Soils with inherent pH values between 6 and 7.5 are ideal for P availability
Plant-growth-promoting bacteria (PGPB) could increase plant tolerance to P deficiency. Microbes (genera Pseudomonas, Bacillus, Rhizobium, Enterobacter, Penicillium, Aspergillus) are involved in converting insoluble soil P into plant-available forms by the excretion of organic acids, hydroxyl ions and CO2.
