Phosphorus is widely unavailable because it rapidly forms insoluble complexes with cations, particularly aluminum and iron under acid conditions
Thus, although bound P is quite abundant in many soils, it is largely unavailable for uptake. As such, P is frequently the most limiting element for plant growth and development.
Plants have evolved a diverse array of strategies to obtain adequate P under limiting conditions, including modifications to root architecture, carbon metabolism and membrane structure, exudation of low molecular weight organic acids, protons and enzymes, and enhanced expression of the numerous genes involved in low-P adaptation
Plants have evolved two broad strategies for P acquisition and use in nutrient-limiting environments: (1) those aimed at conservation of use; and (2) those directed toward enhanced acquisition or uptake (Lajtha & Harrison, 1995; Horst et al., 2001; Vance, 2001). Processes that conserve the use of P involve decreased growth rate, increased growth per unit of P uptake, remobilization of internal Pi, modifications in carbon metabolism that bypass P-requiring steps, and alternative respiratory pathways (Schachtman et al., 1998; Plaxton & Carswell, 1999; Raghothama, 1999;Uhde-Stone et al., 2002a,b). By comparison, processes that lead to enhanced uptake include increased production and secretion of phosphatases, exudation of organic acids, greater root growth along with modified root architecture, expansion of root surface area by prolific development of root hairs, and enhanced expression of Pi transporters (Marschner et al., 1986; Duff et al., 1994; Schachtman et al., 1998; Gilroy & Jones, 2000; Lynch & Brown, 2001).
Allan, D., Uhde-Stone, C., Vance, C., 2003, Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource, New Phytologist, Volume 157, Issue 3, pages 423–447
Deficiency of soil phosphorus is the most important chemical factor restricting plant growth in New South Wales
Colwell, J.D., 1963, The estimation of the phosphorus