While all trees can mitigate climate change by absorbing carbon dioxide, a few have another trick up their sleeve that allows them to turn CO2 into stone. Recent research has shown that certain species of fig trees that grow in Kenya specialize in this hidden talent, which may give CO2 storage efforts an extra boost.
The new research — which will be presented this week at the Goldschmidt geochemistry conference in Prague — is centered on improving C02 sequestration. Since some fig trees can stash atmospheric CO2 as “rocks” in surrounding soil, they show potential to become an unexpected icon for climate change strategies.
Turning Carbon Dioxide into Stone
Whenever trees are involved in climate change dialogue, they’re usually brought up for their ability to remove carbon from the air and use it to create oxygen during photosynthesis. One 2023 study estimated that global forests could hypothetically capture around “226 gigatonnes of carbon in regions with a low human footprint if they were allowed to recover.”
Many conversations on forest recovery, therefore, have this organic carbon sequestration at the forefront. Inorganic carbon sequestration, on the other hand, has not gained nearly the same traction.
This is likely because inorganic carbon sequestration is not something every tree is capable of doing. Only certain trees can utilize CO2 to create calcium oxalate crystals, the first step in a process called the oxalate carbonate pathway. When parts of these trees decay, fungi and microbial communities turn the crystals into calcium carbonate, the primary ingredient that makes up limestone and chalk.
In some cases, termites even help this process come to fruition by carrying fallen leaves to their mounds, where microbes convert the carbon to calcium carbonate and store it underground.
Read More: Trees Don’t Like To Breathe Wildfire Smoke and They’ll Hold Their Breath To Avoid It
Fighting Climate Change with Fig Trees
When the carbon in some trees is turned into calcium carbonate, it increases the soil pH around the tree. The researchers say that this form of inorganic carbon could be a major help for C02 sequestration since it lasts much longer in soil than organic carbon.
The research team pinpointed three species of fig tree grown in Kenya, some of the first fruit trees shown to achieve the oxalate carbonate pathway. They found that calcium carbonate was forming on the exterior of the tree trunks and also deeper within the wood.
“As the calcium carbonate is formed, the soil around the tree becomes more alkaline,” said Mike Rowley, a biogeochemist at the University of Zurich who will be presenting the research, in a press statement. “The calcium carbonate is formed both on the surface of the tree and within the wood structures, likely as microorganisms decompose crystals on the surface and also penetrate deeper into the tree. It shows that inorganic carbon is being sequestered more deeply within the wood than we previously realized.”
Plants with Purpose
One of the fig tree species, Ficus wakefieldii, was particularly effective at sequestering C02. The researchers plan to conduct further tests to determine how well this tree can store CO2 in different environments.
Research on the oxalate carbonate pathway has mainly focused on topical environments and trees that do not produce food, like the Iroko tree on the West Coast of Africa. According to the researchers, this tree can “sequester one ton of calcium carbonate in the soil over its lifetime.”
The researchers suggest that there are likely ample, unexplored opportunities for inorganic carbon sequestration, given that calcium oxalate is a highly abundant biomineral produced by many plants, and the microorganisms that facilitate its conversion to calcium carbonate are also widespread.
By planting more fig trees, the perilous consequences of carbon emissions could potentially be dampened. And in this case, the fruits of C02 sequestration may turn out even sweeter.
Read More: Midwestern U.S. Forests Doubled in Carbon Storage During the Holocene
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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
