Defining the Sphagnum Core Microbiome across the North American Continent Reveals a Central Role for Diazotrophic Methanotrophs in the Nitrogen and Carbon Cycles of Boreal Peatland Ecosystems

Abstract

Nitrogen availability frequently limits photosynthetic production in Sphagnum moss-dominated high-latitude peatlands, which are crucial carbon-sequestering ecosystems at risk to climate change effects. It has been previously suggested that microbial methane-fueled fixation of atmospheric nitrogen (N 2 ) may occur in these ecosystems, but this process and the organisms involved are largely uncharacterized.

Vegetation impacts ditch methane emissions from boreal forestry-drained peatlands—Moss-free ditches have an order-of-magnitude higher emissions than moss-covered ditches

“…The higher fluxes in moss-free than in moss-covered measurement points, and the occurrence of occasional CH 4 sinks in moss-covered points (Figure 1), agree with results from previous studies (Minkkinen and Laine, 2006;Korkiakoski et al, 2020). This may be explained by active CH 4 -consuming bacteria (methanotrophs) living in and on mosses, especially in and on Sphagnum mosses (Raghoebarsing et al, 2005;Kolton et al, 2022), and in water and sediments below the mosses. In fact, the mosscovered measurement points of two study areas, Ränskälänkorpi and Lettosuo, turned into net CH 4 sinks in mid-summer when the WT was at relatively low level (Figures 1A, B; Supplementary Figure S24).…”

Climate drivers alter nitrogen availability in surface peat and decouple N2 fixation from CH4 oxidation in the Sphagnum moss microbiome

“…ASVs belonging to the Methylorosula genus and Methylopilaceae family were among the most enriched taxa in the warmed enclosures (Table S6). While these taxa have been found in diverse environments, they are not commonly associated with Sphagnum mosses (Bragina et al, 2012; Kolton et al, 2022). While these taxa comprised a negligible fraction of the Sphagnum microbiome under ambient conditions, they increased to relative abundances of 3%–6% in the warmest enclosures (Figure S17).…”

“…Sphagnum 's ecological success is due in part to their association with a diverse assemblage of microbial partners that directly support moss productivity and ecosystem function by regulating transformations of C and nitrogen (N) (Bragina et al, 2014; Kolton et al, 2022; Kostka et al, 2016; Warren et al, 2017). Sphagnum ‐associated diazotrophs (N 2 ‐fixing microorganisms) play a critical role in N‐cycling by supplying 30%–96% of the total ecosystem N input to Sphagnum ‐dominated peatlands (Berg et al, 2013; Salmon et al, 2021; Vile et al, 2014).…”

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe

“…These northern latitude ecosystems harbor over one-quarter of terrestrial carbon in the form of peat, or incompletely decomposed biomass, but cover roughly 3% of Earth’s land mass ( 1 ). Furthermore, peatlands store approximately 9 to 16% of global soil nitrogen ( 2 , 3 ), which is largely derived from the biological fixation of atmospheric nitrogen by microbes that live in symbiosis with peat mosses ( 4 , 5 ). Recently, much effort has been dedicated to understanding how Sphagnum will respond to projected scenarios of climate change (e.g., see references 6 and 7 ), but gaps exist in our knowledge about how such changes might affect the community composition and functioning of the Sphagnum microbiome.…”