Original articleMethane oxidation in response to iron reduction-oxidation metabolism in tropical soils

•Iron reduction oxidation cycling stimulated methane oxidation in tropical soil ecosystem.•Low crystalline Fe minerals stimulated methane oxidation by enhancing methanotrophs abundance.•Future climate with intense intermittent wet season would alter CH4 cycling in tropical and subtropical soils.

Experiments were carried out to understand how iron (Fe) reduction-oxidation (IRO) influences CH4 oxidation in soil. Soil samples (alluvial and vertisol) were induced to undergo microbial Fe reduction and aerobic oxidation consecutively for three cycles simulating natural wetting-drying soil cycle. After each IRO cycle, soils were incubated to determine CH4 oxidation rate, Fe mineral and methanotrophs abundance. Potential iron reduction rate k (μM Fe2+ produced g−1 soil d−1) increased from 1.26 to 2.16 in vertisol and 1.95 to 3.05 in alluvial soil. Potential iron oxidation (μM Fe2+ oxidized g−1 soil d−1) increased from 2.33 to 5.70 in vertisol and 2.43 to 9.58 in alluvial soil. The iron reduction-oxidation significantly (p < 0.05) stimulated CH4 oxidation rate k. The high affinity CH4 oxidation rate increased from 0.03 to 0.19. Low affinity CH4 oxidation rate increased from 0.05 to 0.47 in vertisol. A similar effect of IRO on k was observed in alluvial soil. X ray diffraction (XRD) revealed that diffraction intensity of magnetite and goethite decreased over IRO cycle. Real time PCR quantification of methanotrophs (pmoA gene) confirmed that IRO cycle stimulated (p < 0.05) methanotrophs abundance. The study highlights that iron reduction-oxidation cycles can significantly enhance CH4 oxidation in tropical soils.