Role of Synthesis and Exudation of Organic Acids in Phosphorus Nutrition in Plants in Tropical Soils

Plants have evolved a diverse array of strategies to uptake adequate Phosphorus (P) under limiting conditions in tropical and sub-tropical soils, including modifications to root architecture (e.g. cluster roots in Proteaceae), carbon metabolism and membrane structure, exudation of low molecular weight organic acids, protons and enzymes and enhanced expression of numerous genes involved in low-P adaptation. These adaptations seem to be less pronounced in mycorrhizal-associated plants as mycorrhiza in roots significantly helps plants in P uptake at low P soils. The formation of cluster roots in concert with enhanced exudation of low molecular weight organic acids such as citric, oxalic, malic, fumaric, succinic etc. under P-stress by the non-mycorrhizal plants and the accompanying biochemical changes exemplify many of the plant adaptations that enhance P acquisition and use. Several biotechnological approach are now in progress to increase exudation of organic acids from the roots of economically important crop plants for sustainable crop production in tropical and sub-tropical soils.