The influence of Shewanella oneidensis MR-1 on the transformation of iron oxides and phosphorus in a red soil

Abstract

In this study, Shewanella oneidensis MR-1, an iron (Fe)-reducing bacterium, was inoculated to a red soil, which was then incubated. Soil samples were taken regularly to analyse the variation of iron oxides and phosphorus (P) fractions. The results showed that the MR-1 inoculation increased the content of the free iron oxides, but decreased the activity of the iron oxides in the soil, and had no significant influence on the amorphous iron oxides. The MR-1 inoculation increased the resin-P and residual-P, decreased the NaHCO<sub>3</sub>-extracted inorganic P (NaHCO<sub>3</sub>-P<sub>i</sub>) and NaOH-extracted inorganic P (NaOH-P<sub>i</sub>), but did not significantly influence the diluted HCl-extracted inorganic P (D.HCl-P<sub>i</sub>) and concentrated HCl-extracted inorganic P (C.HCl-P<sub>i</sub>). The presence of MR-1 influenced the correlation between the free iron oxides and NaOH-P<sub>i</sub>. In the CK where deactivated MR-1 was applied, there was a significant positive correlation between the free iron oxides and the NaOH-P<sub>i</sub>; in the treatment with the live MR-1 inoculation, there was no correlation between them. In addition, there was a significant positive correlation between the free iron oxides and the C.HCl-P<sub>i</sub>, and there was a significant negative correlation between the NaHCO<sub>3</sub>-P<sub>i</sub>, resin-P, and residual-P. Therefore, the MR-1 inoculation improved the P availability by decreasing the activity of the iron oxides and consequently improved the P use efficiency in the red soil.