This Tree in Kenya Has a Hidden Talent — It Can Convert a Greenhouse Gas Into ‘Chalk’

Running for miles and miles in the arid, nomadic countryside of Samburu, Kenya’s fig trees have recently been found to possess a hidden and rare talent. While most trees slurp up carbon dioxide from the atmosphere and store it inside their bodies, these figs are proud “climate warriors.” They not only store the greenhouse gas within their bodies, but also transform it into the material that you find in the white chalk sticks used in schools. The talent was discovered only recently by a team of scientists who presented their research at the Goldschmidt geochemistry conference in Prague.

The team involved scientists from Kenya, Switzerland, America, and Austria, led by Mike Rowley from the University of Zurich in Switzerland. The team first identified the excellent carbon-trapping skill when they ventured into the Kenyan forest and squirted weak hydrochloric acid onto the trees growing from the depleted basaltic soils of the Samburu Country. After noticing bubbles billowing out from the acid splash, the team deduced that the tree was converting carbon dioxide into calcium carbonate and storing it in its trunk.

The first step the tree used for this conversion was a process called the “oxalate carbonate pathway,” in which it converted the greenhouse gas into calcium oxalate crystals. Once the crystals are formed, fungi, decaying organisms, and microbial communities break down the oxalate crystals, converting them into limestone. Unlike the organic carbon that stays in the ground long after the tree has died, these crystals linger around for longer. This implies that a fig tree offers a “delicious new weapon to the climate change arsenal.” If more and more of these fig trees were planted, either for forestry or fruit, they could contribute a great deal to slowing down climate change.

"We've known about the oxalate carbonate pathway for some time, but its potential for sequestering carbon hasn't been fully considered," Rowley, who’s also a biogeochemist, shared in a press release. For this research, Rowley and his team focused on three species of figs: Ficus wakefieldii, Ficus natalensis, and Ficus glumosa. While all three species are capable of absorbing carbon dioxide from the atmosphere into limestone laced throughout the bark, Ficus wakefieldii became the top performer in terms of carbon fixation rates.

The team believes that adding new species of limestone-producing plants, apart from figs, could also be considered as a wonderful tool in agroforestry. "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," Rowley said.

Now, the team’s hopes are set on tracking and identifying tree species that can also convert “inorganic carbon” apart from “organic carbon” into limestone. "Even in wetter environments, the carbon can still be sequestered," Rowley elaborated. "So far, numerous species of trees have been identified that can form calcium carbonate, but we believe there are many more. This means that the oxalate-carbonate pathway could be a significant, under-explored opportunity to help mitigate CO2 emissions."