The bark of a single tree can host trillions of bacteria, which may have a crucial yet underappreciated role in regulating greenhouse gases in our atmosphere.

Globally, the total surface area of tree bark is estimated to be around 143 million square kilometers, roughly equivalent to the Earth’s total land area. This extensive area represents a vast microbial environment known as the ashosphere, yet the microorganisms residing there have largely been overlooked by researchers. Learn more.

“It may seem obvious, but we’ve historically ignored tree bark,” states Bob Leung, a researcher from Monash University in Melbourne, Australia. “I had never considered that microbes existed in tree bark, but it makes perfect sense. Bacteria thrive everywhere, so it’s reasonable to expect them in the bark as well.”

Leung and his team initiated their research on a common wetland species known as paperbark (Melaleuca quinquenervia). Their findings revealed that over 6 trillion bacteria inhabit every square meter of tree bark, a density comparable to that found in soil.

Genetic testing of 114 bacterial species indicated that most belong to three primary bacterial families: Acidobacteriaceae, Mycobacteriaceae, and Acetobacteriaceae; intriguing as they remain entirely unclassified by science.

A fascinating characteristic of these microorganisms is their ability to metabolize hydrogen, carbon monoxide, and methane for energy. While hydrogen (H₂) itself isn’t a greenhouse gas, it can enhance the warming effect of the atmosphere by reacting with other gases.

Researchers extended their study to include seven additional Australian tree species from diverse habitats, such as Casuarina, rubber trees, and banksias, and assessed their bark’s ability to absorb or emit greenhouse gases both in natural settings and laboratory experiments.

Under aerobic conditions, where oxygen is present, all bark types were found to consume hydrogen, carbon monoxide, and methane. However, when the trees were submerged in water—typical in wetland areas—the microbes adapted by producing these same gases.

Melaleuca quinquenervia trees in an Australian forest”
data-credit=”Luke Jeffrey / Southern Cross University”/>

According to researchers, the collective amount of hydrogen absorbed by bark microorganisms worldwide is estimated to be between 600 million and 1.6 billion kilograms annually, which represents about 2% of the total hydrogen removed from the atmosphere.

This groundbreaking study marks the first effort to evaluate the role of tree bark in atmospheric hydrogen cycling, notes Luke Jeffrey at Southern Cross University in Lismore, Australia.

“Recognizing the hidden contributions of trees, beyond their role in carbon dioxide absorption, is crucial,” emphasizes Jeffrey. “Trees actively engage with other greenhouse gases, which is significant as H₂ interacts with atmospheric methane and could help mitigate the increasing methane dilemma.”

However, the global landscape remains uncertain since the team evaluated only eight tree species from eastern Australia. “Significant research is needed across diverse forest types, tree varieties, microbial communities, and environmental conditions,” says Jeffrey.

Brett Somerelle of the Sydney Botanic Gardens asserts that this research underscores the gaps in our understanding of microbial diversity, composition, and functionality within tree bark ecosystems. “It will be fascinating to observe how these factors change across a broader spectrum of tree species, particularly in arid environments like savannahs and woodlands,” notes Summerell.

Understanding the relationships between fungi and bacteria in tree bark is equally critical, he adds.