Similarly to nitrogen, near all phosphorus present in the plants is found in organic form, being part of structures such as the chloroplast or some metabolite. Very little of P is in an ionic form which is absorbed from the soil:
• Nucleic acids.
• Stimulating role of the roots´ growing.
The main role of phosphorus is structural, being part of the so-called energetic metabolites (ATP). These components storage the energy coming from the photosynthesis and this is liberated in the specific plant sites which is required. Metabolites are fundamental in all processes in which there are active cellular divisions such as apical and root meristems, in the foliar primordia or at the fruit set moment.
In these tissues the local P concentration could be 10 times the plant average, which indicates the high energy supply requirement of them.
Absorption and metabolism form:
In the soil pH of acid type, P is preferable absorbed as H2PO4-, and in the neutral and alkaline pH the predominant form is the H2PO4-. Both forms are used by the plant, even though the most efficient form is H2PO4-. Any way, P is actively absorbed via diffusion and by direct interception mechanisms in the root rhyzosphere. When reaching the leaves, P is incorporated without being reduced to the so-called energetic metabolite components (ATP, ADP and AMP), from where is rapidly mobilized via phloem towards the high required sites mentioned before.