ABSTRACT
In most terrestrial ecosystems, phosphorus (P) is the macronutrient that has the lowest concentration in the soil solution, and for most soil types this is highly buffered. In most terrestrial ecosystems, P is the macronutrient that has the lowest concentration in the soil solution, and for most soil types this is highly buffered. Fertilization has increased the quantity of P in many agricultural soils more than it has increased P availability. In contrast to the high P-use efficiency of many natural ecosystems, there is therefore low P-use efficiency in many agricultural systems. P deficiency stunts the growth first of primary roots and then of shoots, and in Ricinus communis and many other species it induces the production of anthocyanins, so plants tend to become purple-green in color. P starvation increases the P-uptake capacity of many plants by increasing the numbers of transporters with a high affinity for P, whereas low-affinity transporters are generally constitutively expressed.
