Phosphate-solubilizing fungi for efficient soil phosphorus management

P D S U Kumari,C M Nanayakkara

doi:10.4038/sljfa.v3i2.46

Abstract

Rhizosphere soil extracts obtained from eight cinnamon species and three pepper species cultivated organically were inoculated initially on Pikovskaya (PVK) medium. The twelve fungal isolates that solubilized the insoluble phosphates were further tested on the same medium added with both insoluble tricalcium phosphate and soluble dipotassium hydrogen phosphate to detect the expression of the trait in the presence of soluble phosphates in soil, for which all twelve qualified. The efficiencies of phosphate solubilization were investigated in two liquid media: PVK medium to represent soil phosphate pool and a rock phosphate (RP) medium, by determining the available phosphorus concentration in the liquid media at the end of the 24 h and 72 h incubation periods, respectively. The pH reduction in the medium was measured to ascertain the organic acid production by fungal isolates as a mechanism of solubilization. Three fungal isolates showing the highest efficiencies in phosphate solubilization were taxonomically identified based on the micromorphological characteristics and molecular techniques. Two isolates were identified as Penicillium oxalicum and Trichorderma virens and the other was belonging to the genus Aspergillus. A possible synergism between the three fungal species towards phosphate dissolution was detected using the broth culture procedure. Aspergillus sp. in combination with P. oxalicum dissolved both Ca3(PO4)2 and RP recording the highest significant dissolved phosphate levels of 893.43 (±56.768) mg P/L and 309.42 (±42.52) mg P/L, respectively, within 72 h post inoculation, making them prospective candidates for increased phosphate availability of soil phosphate pool and rock phosphates.

Highlights

Absence of plant available phosphates (Pi) is a global agricultural problem, especially due to rapid fixation of applied soluble phosphates in both acidic and alkaline soils (Shen et al, 2011; Son et al, 2006)
As inorganic phosphate (Pi) solubilizing activity of some microorganisms is suppressed by the presence of soluble phosphates in the medium, the isolates were subjected to a secondary screening on a modified PVK medium where tricalcium phosphate was partially replaced by soluble dipotassium hydrogen phosphate (K2HPO4) (Mikanova and Novakova, 2002)
Evaluating the insoluble phosphate solubilization in broth culture The experiment contained two approaches: investigation of efficiency of solubilizing (1) Ca3(PO4)2, which is a close representation of the Phosphate-solubilizing fungi soil P pool and (2) Eppawala Rock Phosphate (ERP), a locally available rock phosphate source

Summary

Introduction

Absence of plant available phosphates (Pi) is a global agricultural problem, especially due to rapid fixation of applied soluble phosphates in both acidic and alkaline soils (Shen et al, 2011; Son et al, 2006). Highly recommended phosphatic fertilizers are known to contain impurities that pose negative impacts on the environment and health (Barabasz et al, 2002; Son et al, 2006; Taylor, 2007).Value addition to rock phosphate and utilization of soil phosphate pool by using biological means were. The ability of Pi dissolution by microorganisms is attributed to the processes of acidification, chelation, enzymatic dissolution and ion exchange reactions (Illmer and Schinner, 1994). The use of such microorganisms as biofertilizers in agriculture is steadily on the rise with increased concern over the environmental problems associated with agrochemical usage worldwide (Chen et al, 2006). Search for ways of increasing plant availability of the existing fixed P pool and Eppawala Rock Phosphate (ERP), a large natural rock phosphate

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Results

Conclusion