Habitat partitioning of marine benthic denitrifier communities in response to oxygen availability

Denitrification is of global significance for the marine nitrogen budget and the main process for nitrogen loss in coastal sediments. This facultative anaerobic respiratory pathway is modular in nature and the final step, the reduction of nitrous oxide (N2 O), is performed by microorganisms with a complete denitrification pathway as well as those only capable of N2 O reduction. Fluctuating oxygen availability is a significant driver of denitrification in sediments, but the effects on the overall N2 O-reducing community that ultimately controls the emission of N2 O from marine sediments is not well known. To investigate the effects of different oxygen regimes on N2 O reducing communities, coastal marine surface sediment was incubated in microcosms under oxic, anoxic or oscillating oxygen conditions in the overlying water for 137 days. Quantification of the genetic potential for denitrification, anammox and respiratory ammonification indicated that denitrification supported nitrogen removal in these sediments. Furthermore, denitrifiers with a complete pathway were identified as the dominant community involved in N2 O reduction, rather than organisms that are only N2 O reducers. Specific lineages within each group were associated with different oxygen regimes suggesting that oxygen availability in the overlying water is associated with habitat partitioning of N2 O reducers in coastal marine surface sediments.