Bark microbiota modulate climate-active gas fluxes in Australian forests

The global surface area of tree bark is approximately equal to the total global land surface area. Though recent studies suggest microbes inhabit tree bark, little is known about their identities, functions, and environmental roles. Here, we reveal, through genome-resolved metagenomics, that tree bark 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 demonstrated that bark microorganisms rapidly aerobically consume methane, hydrogen, and carbon monoxide at in planta concentrations, but can produce these gases under anoxia. Combined with in situ field measurements, we show tree-dwelling microbiota process multiple climate-active gases at significant rates within tree stems, highlighting an important research frontier within global atmospheric cycles.