kenyan fig trees found to lock away co₂ as rock

New Delhi: In a striking new discovery, scientists have found that certain fig trees native to Kenya have a rare ability to lock away carbon dioxide (CO₂) in the form of calcium carbonate—a compound better known as limestone or chalk. This finding, presented at the prestigious Goldschmidt Conference in Prague, could reshape how we think about carbon capture and agroforestry.

The international research team—including experts from Kenya, the U.S., Switzerland, and Austria—revealed that three fig species studied in Kenya’s Samburu County not only absorb CO₂ through photosynthesis but also store it as tiny mineral deposits in their trunks and surrounding soil. These deposits essentially turn parts of the trees into stone.
A natural carbon capture mechanism

This unique process, known as the oxalate-carbonate pathway, involves trees first forming calcium oxalate crystals—a common plant biomineral. When parts of the tree decay, microorganisms such as fungi or bacteria convert these crystals into calcium carbonate. Unlike organic carbon, which eventually decomposes and can re-enter the atmosphere, the inorganic carbon stored as calcium carbonate can remain locked in the soil for centuries.

“Trees have always been seen as carbon sinks through their organic structure,” said Dr. Mike Rowley, senior lecturer at the University of Zurich. “But this inorganic sequestration method adds a whole new layer of potential. If we’re planting trees for food and climate benefits, why not prioritize those that can also lock away CO₂ as rock?”

Fig trees that double as Climate Warriors

Of the fig trees studied, Ficus wakefieldii emerged as the most efficient at storing carbon this way. Using advanced synchrotron radiation analysis at Stanford, researchers observed calcium carbonate forming both on the outside of the trunk and deeper within the wood itself—suggesting carbon is being stored more deeply than previously thought.

Interestingly, this process also raises the pH level of nearby soil, making nutrients more available and potentially improving conditions for other crops—an added bonus for agroforestry.

Next steps: Food, Water, and Climate

With these early findings, the researchers now plan to study how viable these trees are for widespread agroforestry. This includes evaluating their fruit yield, water needs, and how much CO₂ they can realistically sequester under different climate conditions.

Most previous research into the oxalate-carbonate pathway has focused on non-food trees in tropical regions. The first tree discovered to use this pathway was the Iroko (Milicia excelsa), which can store up to one ton of calcium carbonate in its lifetime. But this is the first time such a function has been found in fruit trees with potential for agricultural use.

“Calcium oxalate crystals are common in plants, and the microorganisms that convert them are also widespread,” added Dr. Rowley. “We suspect many more tree species have this ability—it’s just been overlooked. This could be a promising, underutilized tool in the fight against climate change.”

With tree planting becoming a cornerstone of many global climate strategies, this new research opens up the possibility of choosing species not just for shade or fruit, but for their ability to turn CO₂ into stone—literally.