Abstract
Melting permafrost mounds in subarctic palsa mires are thawing under climate warming and have become a substantial source of N(2)O emissions. However, mechanistic insights into the permafrost thaw-induced N(2)O emissions in these unique habitats remain elusive. We demonstrated that N(2)O emission potential in palsa bogs was driven by the bacterial residents of two dominant Sphagnum mosses especially of Sphagnum capillifolium (SC) in the subarctic palsa bog, which responded to endogenous and exogenous Sphagnum factors such as secondary metabolites, nitrogen and carbon sources, temperature, and pH. SC's high N(2)O emission activity was linked with two classes of distinctive hyperactive N(2)O emitters, including Pseudomonas sp. and Enterobacteriaceae bacteria, whose hyperactive N(2)O emitting capability was characterized to be dominantly pH-responsive. As the nosZ gene-harboring emitter, Pseudomonas sp. SC-H2 reached a high level of N(2)O emissions that increased significantly with increasing pH. For emitters lacking the nosZ gene, an Enterobacteriaceae bacterium SC-L1 was more adaptive to natural acidic conditions, and N(2)O emissions also increased with pH. Our study revealed previously unknown hyperactive N(2)O emitters in Sphagnum capillifolium found in melting palsa mound environments, and provided novel insights into SC-associated N(2)O emissions.