Organic Acids in the Rhizosphere: Their Role in Phosphate Dissolution

Phosphorus is an essential plant nutrient that is made available to plants primarily from the soil phosphorus reserves. But its limited mobility in the soil and high fixation capabilities within in the soil matrix necessitate the use of fertilizer forms of phosphorus, which are again prone to fixation, thereby reducing the availability of this crucial element for plant nutrition. Soil microbes play a crucial role in mobilizing various forms of phosphorus (inorganic and organic) and making them available for plant nutrition. Microbe-mediated phosphorus mobilizing processes involve either organic acids that solubilize the inorganic forms of phosphorus or enzymes that mobilize the organic sources of phosphorus. The organic acids that play a crucial role in the dissolution of phosphates can be of plant and microbial origins and vary in their nature and properties depending on the soil, plant, and microbial species involved. Besides playing a crucial role in P cycling, they also perform assorted functions that have a direct bearing on the plant growth and development. This chapter attempts to capture the information on the nature, properties, and functions of organic acids in the rhizosphere.