Fig trees’ intriguing ability to fight climate change
Fig trees do more than grow fruit — they can also help to combat climate change by turning CO₂ into stone in their trunks.
All trees get credit for locking away CO₂ from the atmosphere by photosynthesis and turning it into wood. But fig trees in east Africa have been found to use a special form of photosynthesis that turns CO₂ into crystals of calcium oxalate, and when parts of the tree die and decay these crystals are converted by specialised bacteria and fungi into calcium carbonate, the same mineral as chalk or limestone rocks. Calcium carbonate is long-lasting and does not degrade, so the fig trees can store their carbon deposits out of harm’s way from the atmosphere, offering an intriguing way to fight climate change.
The fig trees create the calcium oxalate crystals on the surface of their trunks and also deep inside their wood. Of three species of fig trees studied, the most efficient at storing CO₂ as calcium carbonate was Ficus wakefieldii, a large tropical tree native to east Africa that grows up to 25 metres high with large leaves. Knowing these fig trees have the power to permanently lock carbon away as a mineral deposit, there are now plans to assess how much carbon dioxide they can store, as well as using them in forestry and producing crops of edible fruit.
Calcium oxalate crystals are actually widespread in plants, found in more than 200 plant families, and the microbes that turn the crystals into calcium carbonate mineral are widespread too. So there may be many other plants and trees that could help get rid of excess CO₂ from the atmosphere and lock it away indefinitely.
What use are the crystals are to plants and trees? One answer is that they protect the plant from insect attacks. The crystals come in a wide array of shapes and sizes, including sharp needles packed in bundles inside the plant cells. If an insect chews the plant, the cells swell up with water and shoot the needles out, stabbing the insect’s soft parts with an onslaught of spears.