Bark microbiota modulate climate-active gas fluxes in Australian forests

Recent studies suggest that microbes inhabit tree bark, yet little is known about their identities, functions, and environmental roles. Here we reveal, through gene-centric and genome-resolved metagenomics, that the bark of eight common Australian tree species hosts abundant and specialized microbial communities. The predominant bacteria are hydrogen-cycling facultative anaerobes adapted to dynamic redox and substrate conditions. Furthermore, bark-associated methanotrophs are abundant and can coexist with hydrogenotrophic methanogens. Microcosm experiments showed that bark microorganisms aerobically consume methane, hydrogen, and carbon monoxide at in planta concentrations and produce these gases under anoxia. Combined with in situ field measurements, we show that tree-dwelling microbiota metabolize multiple climate-active gases at marked rates within tree stems, highlighting a potentially substantial role in global atmospheric cycles.