Cluster root

Proteoid are crowded growing roots that are formed by many plants in phosphate -deficient, to improve phosphate uptake.

Proteoid take their name from the family Proteaceae, where this phenomenon was first observed. This family grows on the very low-phosphorus soils of Australia. The roots are in contrast to most other plants formed close together in a small volume of soil. By the formation of large amounts of organic acids (mainly citric acid), which are supplied as root exudates in the ground, the pH of the soil solution is lowered in this small volume, thereby increasing the solubility of phosphates significantly. This can even be acidified in calcareous soils the rhizosphere, wherein the sparingly soluble calcium phosphate dissolved and converted into calcium citrate.

In addition to phosphorus and iron, manganese and zinc can be mobilized and made ​​available to the plant.

The proteoid may make up 80 percent of the total root mass.

Proteoid expire at the Proteaceae also with representatives of the Myricaceae, the Casuarinaceae, but also in annual legumes such as white lupine ( Lupinus albus). L. albus invests up to 23 percent of their photosynthetic products in the formation of organic acids. If there is sufficient phosphate supply the Proteoid roots are not formed.