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Effectiveness of microbial solubilization of phosphate in enhancing plant phosphate uptake in tropical soils and assessment of the mechanisms of solubilization

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Title:Effectiveness of microbial solubilization of phosphate in enhancing plant phosphate uptake in tropical soils and assessment of the mechanisms of solubilization
Authors:Osorio, Nelson Walter
Date Issued:2008
Description:Thesis (Ph.D.)--University of Hawaii at Manoa, 2008.
A series of experiments were carried out in order to evaluate the effectiveness of a phosphate-solubilizing fungus (PSF), identified as Mortierella sp., to enhance plant phosphate (Pi) uptake and growth. The fungus was isolated from the rhizoplane of Leucaena leucocephala grown in a Hawai'ian Andisol. An in-vitro test was developed to test the capacity of this fungus in dissolving rock phosphate (RP) by means of oxalic acid production in the presence of different types of soil. This PSF could desorb sorbed-Pi from soil mineral surfaces. The presence of high Pi sorbing soil minerals impaired the PSF effectiveness to enhance the supply of soluble Pi. The capacity of the fungus to solubilize P was N-source dependent, being enhanced to a greater extent by ammonium than by nitrate. This PSF was aluminum tolerant and moderately tolerant of low solution pH and its capacity to reduce solution pH and absorb Pi was not affected by these factors.
In contrast, Mortierella sp. alone was able to increase plant growth and Pi uptake of mycorrhiza-free leucaena grown in a low Pi-sorbing Mollisol without RP addition. In summary, four major factors can control the effectiveness of PSM to increase soil solution Pi, plant P uptake and growth: soil Pi sorbing capacity, mycorrizal association, calcium phosphate content of soils, and the use of ammonium as nitrogen source.
In very high Pi sorbing soils (Andisols), Mortierella sp. was not able to increase leucaena growth and Pi uptake, even in the presence of the mycorrhizal association and moderate amounts of RP (P: 300 mg/kg).
Under greenhouse conditions was determined the PSF effectiveness to enhance Pi uptake and growth of mycorrhized (Glomus aggregatum and G. fistulosum) leucaena grown in highly weathered Oxisols. The PSF effectiveness was higher if moderate amounts of RP (P: 150-600 mg/kg) were added to the Oxisol. When RP was not added, the effect of PSF inoculation was not significant. With high amounts of RP (P: 1200 and 2400 mg/kg), the effect of the fungus on leucaena was either nil or negative. Moreover, in the absence of mycorrizal association the effect of PSF inoculation was not significant.
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Appears in Collections: CTAHR Ph.D Dissertations
Ph.D. - Agronomy and Soil Science

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