Phosphorus Solubilization: Mechanisms, Recent Advancement and Future Challenge

Phosphorus deficiency is the limiting factor for crop productivity on more than 40% of arable lands worldwide and using fertilizers is counted as the most popular way to face this problem. The increasing food demand and searching for efficient, cost-effective, and environmental friendly approaches to sustainable agriculture made scientists and farmers take biofertilizers to account for a potent solution. Phosphate-solubilizing microorganisms (PSMs) with the potential of transforming insoluble forms of phosphate to soluble and bioavailable forms are good choices for promoting plant growth with increasing soil soluble P as a major limiting macronutrient. A variety of bacterial and fungal species belongs to PSMs. These organisms are either free organisms in the rhizosphere or live endophytic in external or internal parts of plant tissues. These organisms can act either as free organisms in the rhizosphere or live endophytic in external or internal parts of plant tissues. PSMs use several mechanisms for solubilization and mineralization of inorganic and organic phosphates such as organic acid production, chelation, siderophore production, and excretion of phosphatase and phytase enzymes. Phosphate-solubilizing microorganisms stimulate plant growth by several mechanisms including solubilization of organic P and mineralization of inorganic P, which release soluble P as a nutrient for plants, production of growth-promoting phytohormones such as Indole acetic acid (IAA), ACC deaminase, gibberline and cytokinins; and release of biocontrol agents such as siderophores, antifungal agents and antibiotic. Preparation of profitable microbial inoculants from PSMs, their field application, and challenges in the way of microbial biofertilizer application are from the contents discussed in this chapter. To prevent using biofertilizers failure, an appropriate amount of used inoculants for different plant-soil conditions and different microbial interactions between applied PSMs and other soil inhabitants should be investigated before application.