Phosphorus (P) is an important macronutrient necessary for plant photosynthesis. When present in sufficient quantities, it has been shown to benefit plants by stimulating the formation of oils, sugars and starches, fostering rapid tissue growth and development, increasing stalk and stem strength, improving resistance to disease, enhancing crop quality, aiding flower and seed production, and benefiting a host of other growth- and development-related factors and processes. Out in the real world, however, P availability is often limited. Consequently, plants have developed multiple adaptive mechanisms (morphological, physiological and molecular) to help them cope with P insufficiency (Pi).
Despite such adaptive mechanisms, there are concerns that Pi will increase in the future as atmospheric CO2 concentrations rise. This hypothesis is based upon the recognition that elevated CO2 stimulates plant photosynthesis and growth. Such stimulation, however, is expected to require additional amounts of P in order for plants to sustain the projected CO2-induced growth enhancements. Otherwise, if P is limiting in the growth medium, or if plant adaptive mechanisms cannot compensate for the increased P demand, the growth benefits of CO2 enrichment may be reduced, and possibly wholly overcome, by Pi.