Kenyan fig trees turn CO₂ into stone

At the Goldschmidt Conference, an annual international geochemistry event, being held this year in Prague, Czech Republic, from July 6 to 11, 2025, an international team reveals an extraordinary power of certain varieties of fig trees. These are capable of converting carbon dioxide into... stone. And when they die, the carbon remains in the soil much longer when the carbon dioxide (CO ₂ ) used to make organic matter, such as the trunk, branches, leaves or even roots.

“All trees capture _CO2 from the air, and most of this carbon source goes into molecules that build the plant,” New Scientist points out . “But some trees convert the _CO2 into calcium oxalate, which is converted by bacteria in the tree and soil into calcium carbonate, the main component of rocks like limestone and chalk.”

Not only does the process trap atmospheric carbon dioxide in a stable mineral form, reducing the amount of this greenhouse gas that returns to the atmosphere when the tree dies, but it also increases the soil's pH, which "makes the tree's vicinity healthier and more beneficial for plants and soil microorganisms," explains Earth.com .

It was already known that the iroko tree was capable of sequestering up to a ton of calcium carbonate in the soil over its lifetime thanks to this mechanism. Other trees also make stones, but this is the first time that fruit trees, such as fig trees growing in Kenya, have been shown to do so as well.

“When we plant trees for agroforestry and their ability to store _CO2 as organic carbon while producing food, we might choose trees that provide an additional benefit of sequestering inorganic carbon in the form of calcium carbonate,” explained Mike Rowley of the University of Zurich in Switzerland, who led the study and was quoted as saying by Earth.com .