The inorganic carbon in calcium carbonate typically has a much longer lifetime in the soil than organic carbon
By Andy Corbley-Jul 9, 2025
Some species of fig trees store calcium carbonate in their trunks—essentially turning themselves (partially) into stone.
This ‘auto-petrification’ may offer a strange new way to reduce human carbon emissions, as the mineral created by the trees has a much longer lifespan than organic carbon absorbed and deposited in its root system.
An international team of scientists found that three species of Ficus that grow in Kenya were able to draw carbon dioxide (CO2) from the atmosphere and store it as calcium carbonate ‘rocks’ in the surrounding soil.
The figs are one of the first fruiting trees shown to have this ability, known as the oxalate carbonate pathway. One species in particular, Ficus wakefieldii, was especially prolific.
All trees use photosynthesis to turn CO2 into organic carbon, which forms their trunk, branches, roots and leaves, but certain trees also use CO2 to create calcium oxalate crystals.
When parts of the tree decay, these calcium oxalate crystals are converted by specialized bacteria or fungi into calcium carbonate—the same mineral as limestone or chalk. This increases the soil pH around the tree, while also increasing the availability of certain nutrients.
The inorganic carbon in calcium carbonate typically has a much longer lifetime in the soil than organic carbon, making it a more effective method of CO2 sequestration.
“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, a senior lecturer at the University of Zurich (UZH) who presented his study on the subject at the Goldschmidt Conference in Prague.
Rowley and his team identified how far from the tree the calcium carbonate was being formed and identified the microbial communities involved in the process.
“As the calcium carbonate is formed, the soil around the tree becomes more alkaline,” Dr. Rowley said. “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 realized.”
They are now planning to assess F. wakefieldii’s suitability for agroforestry by quantifying its water requirements and fruit yields and by doing a more detailed analysis of how much CO2 can be sequestered under different conditions.
Most of the research into the oxalate-carbonate pathway has been in tropical habitats and focused on trees that do not produce food. The first tree to be identified as having an active oxalate-carbonate pathway was the Iroko (Milicia excelsa). It can sequester one ton of calcium carbonate in the soil over its lifetime.
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.
“It’s easier to identify calcium carbonate in drier environments,” explained Dr. Rowley.
“However, even in wetter environments, the carbon can still be sequestered. So far, numerous species of tree have been identified which can form calcium carbonate. But we believe there are many more. This means that the oxalate-carbonate pathway could be a significant, underexplored opportunity to help mitigate CO2 emissions as we plant trees for forestry or fruit.”
“While the vine with its clusters was the most characteristic manifestation of Dionysus, he was also a god of trees in general. Thus we are told that almost all the Greeks sacrificed to ‘Dionysus of the tree.’ In Boeotia one of his titles was ‘Dionysus in the tree.’ His image was often merely an upright post, without arms, but draped in a mantle, with a bearded mask to represent the head, and with leafy boughs projecting from the head or body to shew the nature of the deity….
Dionysus in Boeotia, from Daremberg & Saglio’s Dictionnaire des antiquités grecques et romaines, vol. I, pt. 1 (1873, p. 626).
(Source: Charles Daremberg & Edmond Saglio, Public Domain, Internet Archive)
“At Magnesia on the Maeander an image of Dionysus is said to have been found in a plane-tree, which had been broken by the wind. He was the patron of cultivated trees; prayers were offered to him that he would make the trees grow; and he was especially honoured by husbandmen, chiefly fruit-growers, who set up an image of him, in the shape of a natural tree-stump, in their orchards. He was said to have discovered all tree-fruits, amongst which apples and figs are particularly mentioned; and he was referred to as ‘well-fruited,’ ‘he of the green fruit,’ and ‘making the fruit to grow.’ One of his titles was ‘teeming’ or ‘bursting’ (as of sap or blossoms); and there was a Flowery Dionysus in Attica and at Patrae in Achaia. The Athenians sacrificed to him for the prosperity of the fruits of the land. Amongst the trees particularly sacred to him, in addition to the vine, was the pine-tree. The Delphic oracle commanded the Corinthians to worship a particular pine-tree ‘equally with the god,’ so they made two images of Dionysus out of it, with red faces and gilt bodies. In art a wand, tipped with a pine-cone, is commonly carried by the god or his worshippers.
A thyrsus-wielding maenad dangles temptation before a satyr (while trodding on his snake) in the Roman-era Mosaic of the Seasons from Palermo (now found in the Museo archeologico regionale di Palermo).
(Source: Giovanni Dall'Orto, Attribution, via Wikimedia Commons)
“Again, the ivy and the fig-tree were especially associated with him. In the Attic township of Acharnae there was a Dionysus Ivy; at Lacedaemon there was a Fig Dionysus; and in Naxos, where figs were called meilicha, there was a Dionysus Meilichios, the face of whose image was made of fig-wood.”
—J. G. Frazer, Spirits of the Corn & of the Wild, part 1 (The Golden Bough, vol. VII, 1912, p. 2)
Fig trees (Ficus) - Trees that bear fruit without flowering
“Enter the fig forest and seek the flowers, but get none. In the world of the three realms (Trailokya: Ref), you seek the unwavering and you do not get one. The practitioner who knows this, forsakes this and that together...like a snake shedding its old skin.” - Buddha
Above is an extract from a verse of the Buddha in the Sutta Nipata No.5.
A common feature of the fig genus (ficus) is the peculiar inflorescence. They appears as if it suddenly bears fruit without flowering. They are hermaphrodites or dioecious, collectively known as fig trees or figs. These belonging to the family Moraceae have about 850 species and are native throughout the tropics, with a few species also found in semi-temperate zones.
Hermaphrodites are generally those that have male and female reproductive organs in one individual. Those that do not are referred to as gonochoric. In the case of plants, they are referred to as monoicous and dioicous, respectively.
The fig fruit develops as a hollow, fleshy structure called the syconium that is lined internally with numerous unisexual flowers. The tiny flowers bloom inside this cup-like structure. The small fig flowers and later small single-seeded (true) fruits line its interior surface. At maturity, these 'seeds' (actually single-seeded fruits) line the inside of each fig.
The fruit of most species are also edible though they are usually of only local economic importance or eaten as bushfood. However, they are extremely important food resources for wildlife. Figs are also of considerable cultural importance throughout the tropics, both as objects of worship and for their many practical uses.
The Bodhi tree is well known for Siddhartha Gautama (Ref2) sat under the tree, meditated and finally attained enlightenment becoming the Buddha, also known as "sacred fig tree", belongs to this fig family.
My obsession with accuracy, it seems, has led me again to this post. I feel it must be changed to better match how it is I write now. Maybe in two years time, I shall rewrite it once more. Regardless. Welcome or welcome back to the story of my tragic namesake: Syceus.
So, it begins: Syceus was a child of Gaia as well as a Gigante, who were simply men of great strength— despite being oftentimes referred to as ‘giants’— that were notoriously troublesome. These very same Gigantes were quick to take up arms against the Olympians when persuaded by Gaia.
Politics, having been complicated so far back as ancient Greece, would have it so war breaks out between the Gigantes and Olympus.
In short, the Gigantes proved to be a threat to the rule of Zeus, whose victory was not assured until Hercules joined the war. When the odds were favourable to Zeus, Syceus fled to Cilicia to escape his wrath. Wishing to prevent her son from dying at the mercy of Zeus, Gaia hid Syceus in her bosom, turning him into a fig tree.
While this is heavily summarised, being drawn from my entirely unnecessary and excessively sesquipedalian presentation on everyone who got turned into a plant in Greek Mythology, the story is one I have always found to be beautiful. Accentuated, perhaps as I quite like figs.
Not only is the fruit rich in taste and dynamic in appearance, but fig trees have incredible historical significance, being associated with triumph and wisdom for thousands of years. In ancient Greece, fig trees were considered an honour to bestow upon winners of competitions and were seen to shield humans from evil spirits. Odysseus, as it were, was even spared from the lethal whirlpool formed by the sea monster Charybdis by the branches of a single fig tree.
Any opportunity to speak about an arbitrary interest of mine I will take. Mythology, unsurprisingly, is a long withstanding one. Enough that, despite the many changes in my life, my username remains ‘syceusfig’ based on this very story. Will I find myself still unsatisfied with how I have rewritten this? Perhaps. But time will tell, I suppose.