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.