Truncated denitrifiers dominate the denitrification pathway in tundra soil metagenomes

Abstract

AbstractIn contrast to earlier assumptions, there is now mounting evidence for the role of tundra soils as important sources of the greenhouse gas nitrous oxide (N2O). However, the microorganisms involved in the cycling of N2O in this system remain largely uncharacterized. Since tundra soils are variable sources and sinks of N2O we aimed to investigate the links between microbial community structure and N2O cycling in this system. We analysed 1.4 Tb of metagenomic data and manually binned and curated 796 metagenome-assembled genomes (MAGs) from soils in northern Finland covering a range of ecosystems from dry upland soils to water-logged fens. We then searched for MAGs harbouring genes involved in denitrification, an important biotic process driving N2O emissions. Communities of potential denitrifiers were dominated by microorganisms with truncated denitrification pathways (i.e. lacking one or more denitrification genes) and differed across soil ecosystems. Upland soils had a strong N2O sink potential and were dominated by members of the Alphaproteobacteria such as Bradyrhizobium and Reyranella. Fens, which had in general net-zero N2O fluxes, had a high abundance of poorly characterized taxa affiliated with the Chloroflexota lineage Ellin6529 and the Acidobacteriota subdivision Gp23. By coupling an in-depth characterization of microbial communities with in situ measurements of N2O fluxes, our results suggest that the observed spatial patterns of N2O cycling are driven by the composition of denitrifier communities.