Trees are the lungs of the Earth – it is well understood that they extract and contain large amounts of carbon dioxide from the atmosphere. But emerging research shows that trees can also emit methane, and at present it is not known how much.
This could be a major problem, as methane is a greenhouse gas about 45 times more potent than carbon dioxide heating our planet.
However, in a world first discovery published in Nature Communications, we found unique methane-eating communities of bacteria living within the bark of a common Australian tree species: bark (Melaleuca quinquenervia). These microbial communities abounded, prospered, and mitigated about a third of the substantial methane emissions from shellfish that would otherwise end up in the atmosphere.
Because research on tree methane (“treetane”) is still relatively relative, there are many questions to be solved. Our discovery helps fill these critical gaps and will change the way we look at the role of trees in the global methane cycle.
Wait, trees emit methane?
Yes, you read that right! Methane gas in cotton fields was first reported in 1907, but was largely overlooked for nearly a century.
Only in 2018 was a tree-methane review published and then researched into a project, labeling this as a “new limit of the global carbon cycle”. Since then it is gaining rapid momentum, with studies now around the forests of Japan, Britain, Germany, Panama, Finland, China, Australia, the United States, Canada, France and Borneo just to name a few.
Research on tree methane is still relatively relative.
In some cases, theatrical emissions are significant. For example, the tropical Amazon basin is the largest natural source of methane in the world. Trees account for about 50% of its methane emissions.
Likewise, 2020 research found a low subtropical Melaleuca Forests in Australia emit methane at speeds similar to trees in the Amazon.
Dead trees can also emit methane. At the site of a catastrophic climate-related mangrove forest extinction in the Gulf of Carpentaria, dead mangrove trees emitted eight times more methane than living ones. This raises new questions about how climate change can provoke positive reactions, triggering a powerful greenhouse gas emitted by dead and withering trees.
Treethane emissions are most likely to cause some of the major uncertainties in the most recent global methane budget, which attempts to determine where all the methane in the atmosphere comes from. But we are still a long way from refining an answer to this question. Currently trees are not yet included as a distinct emission category.
So where exactly does the treetano come from?
Within wetland forests, scientists have assumed that most treetone trees originate from the subsoils. The methane is transported up through the tree roots and stems, then through the bark to the atmosphere.
We have confirmed, in other recent research, that wetlands have indeed been the source of methane emissions in low forest trees. But this was not always the case.
Some lowland forest trees such as cotton can emit flammable methane directly from their stems, which is likely to be produced by microbes living within the moist trees themselves. Dry forest trees also appear as methane emitters – albeit at much lower speeds.
Discover methane bacteria
For our latest research, we used microbiological extraction techniques to test various microbial communities that live within trees.
We discovered that the bark of bark trees provides a unique home for methane-oxide bacteria – bacteria that “consume” methane and transform it into carbon dioxide, a much less powerful greenhouse gas.
Notably, these bacteria made up up to 25% of total microbial communities living in the bark and consumed about 36% of the tree’s methane. It seems that these microbes live easily in dark, humid and rich methane environments.
This discovery will revolutionize the way we look at methane trees emitting and the new microbes living within them.
Just by understanding why, how, who, when and where trees emit the most methane, we can more effectively plant forests that effectively deplete carbon dioxide while avoiding unwanted methane emissions.
Our discovery that shell-dwelling microbes can mitigate large treetane trees makes this equation difficult, but ensures that microbiomes have evolved within trees to consume methane as well.
Future work will no doubt look further afield, exploring the microbial communities of other forests that emit methane.
Billions of trees to fight climate change
We need to be clear: trees are in no way shaped or bad for our climate and give many other priceless ecosystem benefits. And the amount of methane emitted by trees is generally obscured by the amount of carbon dioxide they will eat during their lifetime.
However, there are currently 3.04 trillion trees on Earth. With both mountainous and lowland forests capable of emitting methane, mere traces of methane worldwide can add up to a large methane source.
Because we now have a global movement aimed at reforesting large areas of the Earth with 1 trillion trees, knowledge of surrounding methane trees is critical.
This article was originally published in The Conversation of Luke Jeffrey at Southern Cross University. Read the original article here.