N(2)O 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.