Management of soil phosphorus and plant adaptation mechanisms to phosphorus stress for sustainable crop production: a review

Abstract

Phosphorus is one of the seventeen essential nutrients required for plant growth.Despite its importance, it is limiting crop yield on more than 40% of the world's arable land.Moreover, global P reserves are being depleted at a higher rate and according to some estimates there will be no soil P reserve by the year 2050.This is a potential threat to sustainable crop production.Most of the P applied in the form of fertilizers may be adsorbed by the soil, and is not available for plants lacking specific adaptations.Available soil P and hence crop yield can, however, be increased through applying P containing fertilizers to feed the ever increasing world population.The P contained in crop residues if left in the field can be recycled by incorporating the residues into the soil whereas part of P in crop residues fed to livestock can be returned back to the soil in the form of manure and as bone meal.Additionally, plants have evolved a diverse array of strategies to obtain adequate P for their growth under P limiting conditions (a term called as P-efficiency mechanisms).Plant P-efficiency mechanisms include both improved uptake efficiency (the ability of a plant to take up more P under P limiting condition) and improved utilization efficiency (the ability of a plant to produce higher dry matter yield per unit P taken up).Uptake efficiency mechanisms include modification of root architecture, development of large root system, longer root hairs and thinner roots, exudation of low molecular weight organic acids, protons and enzymes such as phosphatases and phytases, association with mycorrhiza, production of cluster roots and expression of high affinity P transporters all of which contribute to increased P uptake efficiency of the plant.Other mechanisms include the use of alternative P-independent enzymes and glycolytic pathways, efficient cytoplasmic P homeostasis and higher ability to remobilize P from other plant parts all of which are part of enhanced P utilization efficiency.Traits related to the above morphological, physiological, biochemical and molecular adaptation mechanisms under P stress can be utilized in improving cultivated crops for P efficiency through breeding programs.