Microorganisms in the phyllosphere of Norway spruce controlling nitrous oxide dynamics

Current climate change assessments and greenhouse gas flux models often lack information on the microbiological processes that consume atmospheric nitrous oxide (N₂O), a potent greenhouse gas. There is limited understanding of phyllospheric microorganisms controlling N₂O exchange. In this study, we determined the microbial potential for N₂O consumption in aboveground vegetation in boreal forests. For this, we collected shoot samples from upland spruce forests in Finland and used a novel targeted metagenomics approach with a hybridization capture of gene-specific probes. Most of the samples contained nosZ genes, encoding the N₂O reductase. Phylogenetic placement showed a significantly higher relative abundance (P < .01) of nosZ Clade I than nosZ Clade II. Bacterial members such as Comamonadaceae, Hydrogenophaga, and Paracoccus, which all harbor nosZ Clade I, were found in high relative abundance in the spruce shoots across the sites, suggesting they play a role in N₂O consumption capabilities in the spruce phyllosphere. Anoxic incubations, utilizing gas chromatography for N₂O analyses, showed potential N₂O consumption activity across the spruce samples. The presence of nirK and nirS suggests potential for denitrification, possibly resulting in N₂O production. Our finding provides evidence of microbial communities in spruce canopies with potential for N₂O exchange. Given the vast coverage of boreal forests globally, understanding the role of phyllospheric microorganisms in N₂O exchange is crucial for improving the accuracy of greenhouse gas models and enhancing climate prediction reliability.