Phosphorus (P) is an essential nutrient element and one of the major limiting factors in agricultural production. Because of phosphorus reactivity, it bounds into un-available forms after fertilizer application. We can concur this problem by using of phosphorus-solubilizing microorganisms. Phosphorus-solubilizing microorganisms are group of beneficial microorganisms, which are able of transforming inorganic and organic forms of insoluble phosphorus into soluble forms. Most of soil phosphorus is in unavailable to plants and to transfer in ecosystem. Main mechanism of phosphorus-solubilizing microorganisms is exudation of organic acids that make phosphorus available by lowering the pH of soil. Other mechanisms are exudation of siderophores (Fe3+ chelating molecules), that are responsible for solubility of inorganic phosphorus and enzymes, which are important for solubility of organic phosphorus. In acid soils phosphorus bounds to form iron and aluminum oxides and in alkaline soils it precipitates to form calcium phosphate. The most important genera of phosphorus-soluble bacteria are Bacillus and Pseudomonas and the most important genera of phosphorus-solubilizing fungi are Aspergillus and Penicillium. Arbuscular mycorrhizal fungi can substantially increase supply of phosphorus to plants. Inoculation of Triticum aestivum seeds with Bacillus and Azotobacter can result in higher yields of grain up to 40 %. Most of laboratory studies points toward effectiveness of phosphorus-solubilizing microorganisms. However, scientists in field experiments do not have the same results. The main reason is high buffering capacity of soil and therefore, microorganisms are not able to exudate enough organic acids into the soil to solubilize phosphorus. This thesis focuses on phosphate-solubilizing microorganisms and their mechanisms on phosphorus solubility and their plant growth promotion.
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