- A new study carried out in Australia finds that the bark of common tree species holds diverse microbial communities, with trillions of microbes living on every tree.
- The research determined that many of these microbial species specialize in metabolizing methane, hydrogen, carbon monoxide and volatile organic compounds (VOCs).
- Methane is a powerful greenhouse gas, while hydrogen and carbon monoxide are considered indirect greenhouse gases. Carbon monoxide and VOCs are also both hazardous to human health.
- The study found that tree bark microbes play a significant, previously unknown role in atmospheric gas cycling, potentially boosting estimations of the climate benefits offered by global forests. Learning which tree species boast the best microbes for curbing climate change and pollution could better inform reforestation strategies.
Microbes living in tree bark consume vast amounts of climate-related and toxic gases, according to new research published Jan. 8 in Science.
In the past, tree bark was considered little more than an inert protective covering for trees and unlikely to support significant microbial life. But over the last decade, research has found that microbes not only thrive in tree bark, but they consume methane, a phenomenon significant on a global scale.
This knowledge caused scientists at Australia’s Monash and Southern Cross universities to wonder if microbial communities living in tree bark might also be utilizing and absorbing other ubiquitous atmospheric gases, a line of reasoning that turned out to be “spot on,” says Pok Man Leung, a research fellow at Monash University and the study’s co-lead author.
The research team sampled the bark of eight common Australian trees across different biomes in subtropical eastern Australia. They then used metagenetics along with laboratory and field-based measurements of gas fluxes to determine what kinds of microbes lived in the bark, and what they were doing.
They found that the trees’ bark was brimming with microbes that digest methane, hydrogen, carbon monoxide and volatile organic compounds (VOCs). Methane is at least 20 times more potent as carbon dioxide as a greenhouse gas, while hydrogen and carbon monoxide are considered indirect greenhouse gases. Carbon monoxide and VOCs are both harmful to human health.
“It totally revises our understanding that trees are not just absorbing CO2, but with the microbes that live on the surface, can also remove multiple other greenhouse gases,” Leung says. “So the climate benefit of trees may be huge, and there’s a lot of potential that we can leverage to mitigate climate change.”
In the Australian study, all the trees tested hosted abundant microbial communities, up to around 6 trillion microbes per square meter of bark. Researchers also determined these microbial communities were unique to the bark and distinct from those found in nearby soil or water, with some of the tree bark microbes previously undescribed.
The researchers also looked for enzymes that indicate what type of food the microbes are designed to digest. While wetland trees were the most likely to harbor methane-specialized bacteria, all the trees sampled contained microbes that utilize hydrogen.
“Discovering that hydrogen consumption was consistent no matter which sort of forest type we were looking at was very exciting,” says Luke Jeffrey, postdoctoral research fellow at Southern Cross University and co-lead author on the study. That’s significant because hydrogen indirectly contributes to global warming by altering the abundance of methane and other greenhouse gases.
Globally, the surface area of tree bark is similar to that of all land on earth. The study suggests that tree bark microbes could remove from 0.8% to 2% of total atmospheric hydrogen per year.
“This work extends the known microbiome of trees and demonstrates that bark has microbial populations to metabolize atmospheric gases, including methane, which could make a difference in the [global] methane budget and climate change models,” Lisa Stein writes in an email; Stein is a professor at the University of Alberta and Canada Research Chair in Climate Change Microbiology, and not involved in the current research. “To me, this study confirms that we occupy a predominantly microbial world that is operating in harmony with every life form and ecosystem on the planet.”
One scientific priority going forward, Jeffrey says, will be to expand the scale and reach of this line of research to other habitats around the world. The Southern Cross and Monash University team is already looking at tree bark microbes in Australia’s more tropical areas. They’re also exploring if, and how, some microbes might utilize nitrous oxide, another potent greenhouse gas.
The current research also raises questions as to how tree bark microbes might be affected by climate change. If, for example, climate change-driven wetter conditions lead to forests becoming flooded, that could result in more frequent low oxygen conditions, creating a positive feedback loop, Leung says, as tree bark microbes switch from absorbing gases to gas production. But he added that more research is needed to understand this process.
The new research suggests some promising practical applications. Figuring out which tree species host which types of gas-absorbing microbes could help determine which tree species would be most effective in reforestation efforts to combat climate change, Leung says. Planting the right tree species in urban areas could also help reduce pollution by removing toxic gases like carbon monoxide and VOCs.
“That will be the ultimate goal, to find the right tree, and … the right conditions that really help promote trees’ and microbes’ capacity in [protecting] our climate,” Leung says.
Banner image: Study co-lead author Luke Jeffrey climbs a tree in a melaleuca wetland forest to measure microbial community gas fluxes. Image courtesy of Luke Jeffrey/Southern Cross University.
Citations:
Leung, P. M., Jeffrey, L. C., Bay, S. K., Gomez-Alvarez, P., Hall, M., Johnston, S. G., … Greening, C. (2026). Bark microbiota modulate climate-active gas fluxes in Australian forests. Science, 391(6781). doi:10.1126/science.adu2182
Jeffrey, L. C., Maher, D. T., Chiri, E., Leung, P. M., Nauer, P. A., Arndt, S. K., … Johnston, S. G. (2020). Bark-dwelling methanotrophic bacteria decrease methane emissions from trees. doi:10.21203/rs.3.rs-119818/v1
Gauci, V., Pangala, S. R., Shenkin, A., Barba, J., Bastviken, D., Figueiredo, V., … Malhi, Y. (2024). Global atmospheric methane uptake by upland tree Woody surfaces. Nature, 631(8022), 796-800. doi:10.1038/s41586-024-07592-w
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