Phosphate solubilizing microorganisms Use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants. Introduction Plants acquire P from soil solution as phosphate anion. It is the least mobile element in plant and
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Presentation Transcript
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Phosphate solubilizing microorganisms Use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants.<br>
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Introduction Plants acquire P from soil solution as phosphate anion.
It is the least mobile element in plant and soil.
It precipitates in soil as orthophosphate or is adsorbed by Fe & Al oxides through legand exchange.
P solubilizing microbes play role in phosphorus nutrition by enhancing its availability to plants through release from inorganic and organic soil P pools by solubilization and mineralization.<br>
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Phosphate Solubilization Soil P dynamics is characterized by physicochemical (sorption-desorption) and biological (immobilization-mineralization) processes.
Soil microorganisms play a key role in soil P dynamics and subsequent availability of phosphate to plants.
P forms are tri-calcium phosphate, di-calcium phosphate, hydroxyapatite, and rock phosphate<br>
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Phosphate solubilizing bacteria (PSB) are being used as biofertilizer since 1950s.
Bacteria are more effective in P solubilization than fungi.
PSB constitute 1 to 50 %,
while phosphorus solubilizing fungi (PSF) are only 0.1 to 0.5 % in P solubilization potential.<br>
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Mechanisms of phosphate solubilization Principal mechanism in soil for mineral P solubilization is lowering of soil pH by microbial production of organic acids and mineralization of organic P by acid phosphatases.
Most frequent agent of mineral phosphate solubilization are Gluconic acid & 2-Ketogluconic acid.
Other organic acids produced by bacteria are lactic, isovaleric, isobutyric, acetic acids, glycolic, oxalic, malonic, and succinic acid.<br>
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Microbial strains producing organic acid<br>
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Inorganic forms of P are solubilized by a group of heterotrophic microorganisms excreting organic acids that dissolve phosphatic minerals and/or chelate cationic partners of the P ions i.e. PO43- directly, releasing P into solution.
PSB inoculants/biofertilizers hold great prospects for sustaining crop production with optimized P fertilization.<br>
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Soil P mobilization and immobilization by bacteria<br>
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Microorganisms involved in phosphorus acquisition include mycorrhizal fungi and PSMs.
Among the soil bacterial communities, ectorhizospheric strains from Pseudomonas and Bacilli, and endosymbiotic rhizobia have been described as effective phosphate solubilizers.
Strains from bacterial genera Pseudomonas, Bacillus, Rhizobium and Enterobacter along with Penicillium and Aspergillus fungi are the most powerful P solubilizers.
Bacillus megaterium, B. circulans, B. subtilis, B. polymyxa, B. sircalmous, Pseudomonas striata, and Enterobacter could be referred as the most important strains.
A nematofungus Arthrobotrys oligospora also has the ability to solubilize the phosphate rocks.<br>
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Occurrence of Phosphate Solubilizing Bacteria High proportion of PSM is concentrated in the rhizosphere.<br>
