In Kenya’s arid north, scientists have discovered that certain fig trees do more than bear fruit; they turn carbon dioxide into stone, locking it away underground in a natural process that is promising to change reforestation practices and redefine climate action.
A team of scientists from Kenya, the US, Austria, and Switzerland has found that some species of fig trees could draw carbon dioxide (CO2) from the atmosphere and store it as calcium carbonate ‘rocks’ in the surrounding soil.
The trees, native to Kenya, are one of the first fruit trees shown to have this ability, known as the oxalate carbonate pathway, in the research to be presented this week at the Goldschmidt conference in Prague.
According to research, certain trees also utilize CO2 to form calcium oxalate crystals, which increases the soil pH around the tree and enhances the availability of specific nutrients. This discovery has promises to introduce new ventures in carbon sequestration as the inorganic carbon in calcium carbonate typically has a much longer lifetime in the soil than organic carbon.
The team, from UZH, the Nairobi Technical University of Kenya, Sadhana Forest, Lawrence Berkeley National Laboratory, University of California, Davis, and the University of Neuchatel, studied three species of fig tree grown in Samburu County, Kenya.
Dr Mike Rowley, senior lecturer at the University of Zurich (UZH), explains, “As the calcium carbonate is formed, the soil around the tree becomes more alkaline. 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.”
He further adds that this shows that inorganic carbon is being sequestered more deeply within the wood than we previously realized.
Calcium oxalate is one of the most abundant biominerals, and the crystals are produced by many plants. The microorganisms that convert calcium oxalate to calcium carbonate are also widespread, and according to the researchers, it is easier to identify calcium carbonate in drier environments.
However, Dr. Rowley says the carbon can still be sequestered even in wetter environments. He adds that the oxalate-carbonate pathway could be a significant, underexplored opportunity to help mitigate CO2 emissions as we plant trees for forestry or fruit.
Of the three types of fig tree studied, the scientists found that Ficus wakefieldii was the most effective at sequestering CO2 as calcium carbonate. They now intend to evaluate the tree’s potential for agroforestry by measuring its water needs and fruit production, as well as conducting a more in-depth study of how much CO2 it can capture under varying conditions.
By leveraging the oxalate-carbonate pathway, these native Kenyan species could play a significant role in long-term CO₂ storage, particularly in regions where reforestation and food security are closely linked.
