Plant mechanisms and mycorrhizal symbioses to increase phosphorus uptake efficiency

The tendency of phosphorus (P) to undergo adsorption and precipitation reactions in soil makes it one of the most immobile of the essential plant nutrients. As a result, the concentration of available P in soil solution is usually very low even though the total P content of soils is generally high. Consequently, P is second only to N in limiting crop productivity. In areas of the world such as the North America and Europe in which P fertilizers are applied liberally to agricultural fields, the loss of this nutrient through its transport in particulate and soluble forms from agricultural fields to lakes and rivers is of concern due to accelerated eutrophication. The need to provide crops with adequate P combined with the desire to minimize the adverse effect of P on the environment will require strategies to reduce P inputs and to maximize the efficiency of P uptake mechanisms in plants. Recent advances in molecular biology offer opportunities to manipulate plants to increase uptake efficiencies of P. Integration of arbuscular mycorrhizal fungi into cropping systems provides an alternative means of maintaining yields while reducing P inputs. To realize the potential of these new technologies, however, a thorough understanding of both soil and plant factors involved in P uptake, and the effects of cultural practices on arbuscular mycorrhizal associations are needed. A review of the literature was undertaken to summarize the relevant state of knowledge on P uptake processes in plants and the mechanisms by which P uptake efficiencies could be enhanced, with particular emphasis on arbuscular mycorrhizal fungi.