Tree tissues and species traits modulate the microbial methane-cycling communities of the tree phyllosphere.

Methanogenic and methane-oxidizing communities (i.e., the microbial communities involved in methane production and consumption) of the tree phyllosphere remain uncharacterized for most tree species despite increasing evidence of their role in regulating tree methane fluxes. Using 16S rRNA gene sequencing, we studied the methanogenic and methane-oxidizing communities of leaves, wood, and bark of five tree species (Acer saccharinum, Fraxinus nigra, Ulmus americana, Salix nigra, and Populus spp.) growing in the floodplain of Lake St-Pierre (Québec) and assessed their relationships with plant traits. Methane-cycling communities differed primarily between tree tissues (leaf, wood, and bark) but also between tree species according to different traits (e.g., leaf, heartwood and bark pH, leaf humidity). Methanogens were prevalent in wood, while methane-oxidizing taxa were found at higher proportions in leaves and bark. Tissue pH was a particularly important trait modulating methane-cycling community composition and the relative abundance of methanogens and methane-oxidizing taxa in the different phyllosphere compartments. Overall, our study shows that methanogens and methane-oxidizing taxa are prevalent in the phyllosphere of several tree species, suggesting a potential widespread role in the regulation of tree methane fluxes. Better understanding these microbial communities and their drivers can help assess their potential contribution to methane-flux regulation.