Role of phosphorus solubilizing microorganisms and dissolution of insoluble phosphorus in soil

Phosphorus is the second important key element after nitrogen as a mineral nutrient in terms of quantitative plant requirement and most commonly limiting the growth of crops. Although abundant in soils, in both organic and inorganic forms, its availability is restricted as it occurs mostly in insoluble forms On average, the phosphorus content of soil is about 0.05% (w/w); however, only 0.1% of this phosphorus is available for plant use. The majority of the applied fertilizer phosphorus is not available to plants and the addition of inorganic fertilizers in excess of the amount that is commonly employed to overcome this effect can lead to environmental problems such as, groundwater contamination and waterway eutrophication. It is therefore of great interest to investigate management strategies that are capable of improving phosphorus fertilization efficiency, increase crop yields and reduce environmental pollution caused by phosphorus loss from the soil. Soil microorganisms enhance plant nutrient acquisition. They are involved in a wide range of biological processes including the transformation of insoluble soil nutrients. In the natural environment numerous microorganisms in the soil and rhizosphere are effective in releasing phosphorus from insoluble soil phosphorus through solubilization and mineralization. These groups of microorganisms are referred to as Phosphorus Solubilizing Microorganisms (PSM). Many species of soil fungi and bacteria are able to solubilize phosphorus in vitro and some of them can mobilize phosphorus in plants. PSM increase the bioavailability of soil insoluble phosphorus for plant use. They solubilize insoluble inorganic (mineral) phosphorus. Phosphate solubilizing/mineralizing microorganisms is therefore a promising strategy for the improvement of plant absorption of phosphorus and thereby reducing the use of chemical fertilizers that have a negative impact on the environment. Production of different types of organic acids by PSM and indirectly by other soil organisms in the main cause of phosphorus solubilization. Phosphorus solubilizers benefits cereals as well as legumes inoculation with Rhizobium.