N2O formation by nitrite-induced (chemo)denitrification in coastal marine sediment

Nitrous oxide (N 2 O) is a potent greenhouse gas that also contributes to stratospheric ozone depletion. Besides microbial denitrification, abiotic nitrite reduction by Fe(II) (chemodenitrification) has the potential to be an important source of N 2 O. Here, using microcosms, we quantified N 2 O formation in coastal marine sediments under typical summer temperatures. Comparison between gamma-radiated and microbially-active microcosm experiments revealed that at least 15–25% of total N 2 O formation was caused by chemodenitrification, whereas 75–85% of total N 2 O was potentially produced by microbial N-transformation processes. An increase in (chemo)denitrification-based N 2 O formation and associated Fe(II) oxidation caused an upregulation of N 2 O reductase (typical nosZ ) genes and a distinct community shift to potential Fe(III)-reducers ( Arcobacter ), Fe(II)-oxidizers ( Sulfurimonas ), and nitrate/nitrite-reducing microorganisms ( Marinobacter ). Our study suggests that chemodenitrification contributes substantially to N 2 O formation from marine sediments and significantly influences the N- and Fe-cycling microbial community.