Phosphorus

Phosphorus is an essential part of genetic material, playing a structural role in the diester bonds present in the nucleic acids DNA and RNA. Therefore, P is especially necessary during times when a large number of cells are dividing in the plant, since the genetic material is duplicated with each division.

Phosphorus plays a key role in energy metabolism, photosynthesis, and respiration by forming the energy-rich anhydride bonds in ATP or ADP molecules.

It is also a fundamental part of phospholipids, essential in the activation of enzymes and in the structure of the cell membrane.

ABSORPTION

Phosphorus can be absorbed by both roots and leaves, with root absorption being the most common method in nature. P is absorbed preferentially as H2PO4- in soils with a pH below 7, and as HPO4-2 in alkaline soils with a pH above 7.

Mycorrhizae, a symbiotic association between soil fungi and plant roots, facilitate the absorption of phosphorus from the soil.

When phosphorus is deficient, the plant moves phosphorus from one organ to another, accumulating in flowers, developing seeds, and young leaves. Consequently, the first symptoms appear on older leaves. These symptoms consist of a blackish-brown coloration on the upper leaves or a purplish coloration on the underside, with the entire leaf darkening. As P deficiency progresses, plant growth is severely reduced.

EXCESS

Unlike nitrogen, excess phosphorus causes the plant to develop roots in excess of the aerial part, resulting in a low aerial part-to-root ratio.