Researchers have found that certain fig trees native to Kenya have the remarkable ability to partially turn themselves into stone—while simultaneously producing fruit and fighting climate change.
Researchers have found that certain fig trees native to Kenya have the remarkable ability to partially turn themselves into stone—while simultaneously producing fruit and fighting climate change. These trees, by harnessing a natural biochemical trick, can convert atmospheric carbon dioxide into solid mineral deposits buried in their own trunks and nearby soil.
Scientists from Kenya, Switzerland, Austria, and the US revealed this natural carbon-capturing alchemy at the prestigious Goldschmidt Conference in Prague. Their study shows that the trees deploy a little-known mechanism called the oxalate-carbonate pathway, which allows them to store carbon in the form of calcium carbonate—the same mineral found in limestone and chalk.
Fig trees and climate change
While all trees use photosynthesis to convert CO₂ into organic carbon, which builds their wood and leaves, a few including these figs produce calcium oxalate crystals, which, upon decaying, are transformed by specialized bacteria and fungi into stable, inorganic calcium carbonate. This chalky compound not only enriches the soil by making it more alkaline and nutrient-rich but also locks carbon away far longer than traditional organic methods.
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“We’ve known about the oxalate carbonate pathway for some time, but its potential for sequestering carbon hasn’t been fully considered. If we’re planting trees for agroforestry and their ability to store CO₂ as organic carbon, while producing food, we could choose trees that provide an additional benefit by sequestering inorganic carbon also, in the form of calcium carbonate,” said Dr. Mike Rowley, senior lecturer at the University of Zurich, who led the study.
The team examined three fig species growing in Kenya’s Samburu County. Using cutting-edge synchrotron analysis at the Stanford Synchrotron Radiation Lightsource, they discovered calcium carbonate forming not just on the bark but also deep inside the wood. The most efficient of the three species was Ficus wakefieldii, which showed significant promise in both CO₂ sequestration and fruit production.
“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. It shows that inorganic carbon is being sequestered more deeply within the wood than we previously realised,” Dr. Rowley added.
Until now, most studies on the oxalate-carbonate pathway focused on non-fruit-bearing tropical trees, like the Iroko (Milicia excelsa), which can store up to a ton of calcium carbonate during its lifetime. This new research marks a significant breakthrough—proving that even productive fruit trees can be powerful climate allies.
Calcium oxalate crystals are common across the plant kingdom, and the microbes responsible for converting them into stone-like carbonate are also widespread. According to Dr. Rowley, “It’s easier to identify calcium carbonate in drier environments. However, even in wetter environments, the carbon can still be sequestered."
