Effect of Nitrogen Form on the Effectiveness of a Phosphate-Solubilizing Fungus to Dissolve Rock Phosphate

Mitiku Habte Nelson Walter

doi:10.4172/2155-6202.10000127

Abstract

An in vitro experiment was carried out to evaluate the effect of nitrogen (N) form (NH4+ and/or NO3-) on the dissolution of rock phosphate (RP) by a phosphate solubilizing fungus (PSF) identified as Mortierella sp. In the presence of NH4Cl or NH4NO3, the solution of pH significantly decreased from an initial value of 7.6 to 3.4 and 3.7 respectively. In the presence of KNO3, the pH went down only to 6.7. As a result, significantly more P was detected in solution in the presence of NH4Cl (129.65 mg/L) than in the presence of NH4NO3 (109.25 mg/L). The concentration of P in solution in the presence of KNO3 was only 0.08 mg/L. The excess of NH4+ adversely affected the growth of Mortierella sp. However, this may have promoted a more active H+-pumping that decreased solution’s pH. In the presence of NO3- as the only source of N, Mortierella sp. not only dissolved a small amount of Pi from the RP but also immobilized most of it into its mycelia. In contrast, in the presence of NH4Cl, Mortierella sp. was effective to dissolve RP and the Pi released remaining in solution while only a little portion was immobilized by the fungal mycelia.

Highlights

Soil phosphate deficiency is globally a major constraint for agriculture, in the tropical regions [1,2,3]
Given the limited N supply of most soils [23,24], the N applied either as NO3- or NH4+ fertilizers can control the extent of acid production by phosphatesolubilizing microorganisms (PSM), which is crucial in the efforts to evaluate the suitability of Mortierella sp. as an effective rock phosphate (RP) solubilizer in the rhizosphere or for its use in the biotechnological production of bio-acidulated RP [25]
When the fungus grew in the presence of NH4Cl or NH4NO3, the pH went down to 3.4 and 3.7, respectively; while in the presence of KNO3 the pH went down only to 6.7

Summary

Introduction

Soil phosphate deficiency is globally a major constraint for agriculture, in the tropical regions [1,2,3]. There is an increasing interest in developing strategies to improve the effectiveness of RP as a direct source of Pi for plant growth in parts of the tropics endowed with local deposits of the material [4,6,7,8,9,10]. One of the biotechnological strategies involve the use of phosphatesolubilizing microorganisms (PSM) [2,11,12,13,14,15,16,17]. Given the limited N supply of most soils [23,24], the N applied either as NO3- or NH4+ fertilizers can control the extent of acid production by PSM, which is crucial in the efforts to evaluate the suitability of Mortierella sp. As an effective RP solubilizer in the rhizosphere or for its use in the biotechnological production of bio-acidulated RP [25] Given the limited N supply of most soils [23,24], the N applied either as NO3- or NH4+ fertilizers can control the extent of acid production by PSM, which is crucial in the efforts to evaluate the suitability of Mortierella sp. as an effective RP solubilizer in the rhizosphere or for its use in the biotechnological production of bio-acidulated RP [25]

Methods

Results

Conclusion