Saturday, 15 July 2006

Abundance and Distribution of Phosphate Solubilizing Bacteria and Fungi in Some Soil Samples from North of Iran.

Alireza Fallah, SWRI, N. Kargar Ave., Tehran, Iran

Phosphorus ranks third after nitrogen and potassium with regard the extent of its requirement by plants and microorganisms and functions most importantly in energy production and transfer. A great portion of phosphorus from chemical fertilizers becomes insoluble turning into calcium or magnesium salts in calcareous soils and iron or aluminium salts in acid environments all of which are unavailable to plants. To transform the insoluble forms of phosphorus into soluble forms, Phosphorus Solubilizing Microorganisms (PSM) would be essential. The soil bacteria and fungi comprise the greatest percentages of phosphate solublizing microorganisms, known as PSM or Phosphate Solubilizing Bacteria (PSB) and Phosphate Solubilizing Fungi (PSF). These microorganisms are capable of solubilizing insoluble compounds and release phosphorus to soil solution. This research was undertaken to fill the gap that exists in the information about the presence and population densities of phosphate solubilizing microorganisms, total soil bacteria and total fungi in various regions of North of Iran. Fifty soil samples were collected from various locations in soils of Iran. Total populations of the bacteria, PSB, the total populations for fungi as well as PSF were determined in all 50 soil samples. Total bacterial populations varied from 106 to 109 cells /g soil, with an average value of 5.82*107 cells /g. The PSB populations ranged from 0 to 107 cells/g soil with some 94% of the samples containing PSB microorganisms. The soil sample from Berry cultivated region contained the greatest PSB population equaling 3.85* 106 cells/g soil. The average ratios of PSB to total bacteria and to total phosphate solubilizing microorganisms were 3.98% and 88.04% respectively. The total fungi populations varied from 102 to 106 cells/g soil, with the lowest population of 6.4*102 cells/g soil coming from a forest area, and the greatest population of 2.73*106 cells/g soil coming from the fermenting residues of a tea processing plant. The average value for total fungi populations was calculated to be 1.92*105 cells/g soil in the collected samples. The total fungi population in 82% of the samples were below this average value. Eighty six percent of the soil samples contained PSF ranging up to 106 cells/g. the greatest PSF population of 1.8 105 cells/g was also found in the fermenting residues of the tea processing plant. The average ratios of PSF to total fungi populations and the total phosphate solubilizing microorganisms were 15.3% and 9.96% respectively. Bacteria comprised the greatest percentage of phosphate solubilizing microorganisms in the soil samples that were examined.

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