Contribution of Iron in Clay Minerals to Redox Cycle in Paddy Soils: Enhancement of Nitrogen-fixation by Iron-reducing Bacteria

Abstract

Iron (Fe) is the most abundant element on Earth and the redox reactions between Fe(II) and Fe(III) are very important from a geochemical point of view. The redox state of Fe has a significant influence on the behavior of various elements in the surface soil environment (e.g., arsenic and potassium. However, until now, redox reactions of structural Fe in clay minerals (Stucki, 2011) and ferrihydrite in paddy soils have been focused on only separately. In this study, we investigated to what extent structural Fe in clay minerals contributes to the overall redox reactions in paddy soils. This study also focused on microbial Fe interactions, in particular, catabolic reduction of Fe by Fe-reducing bacteria in paddy soils and the associated nitrogen-fixation (Masuda et al., 2017). In this study, we investigated whether structural Fe(III) in clay minerals, in addition to hematite and ferrihydrite investigated by Masuda et al. (2021), is available to Fe-reducing bacteria, and whether structural Fe(III) in clay minerals enhances their nitrogen-fixing activity.