Methane oxidation and methane driven redox process during sequential reduction of a flooded soil ecosystem

A laboratory incubation study conducted to assess the temporal variation of CH4 oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO3− reduction, Fe3+ reduction, SO42− reduction and CH4 production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH4 oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH4 oxidation rate (k) was stimulated by 29 % during 5 days (NO3− reduction) and 32 % during both 10 days (Fe3+) and 20 days (early SO42− reduction) over unreduced slurry. CH4 oxidation was inhibited at the later methanogenic period. Contrastingly, CH4 oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH4 oxidation. Higher CH4 oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs (r = 0.994, p < 0.01) and ammonium oxidizers population (r = 0.184, p < 0.05). Effect of electron donors NH4+, Fe2+, S2− on CH4 oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH4 oxidation as well as increased the abundance of methanotrophic microbial population except S2− which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem.