Call it the wood wide web. Although we think of trees as competing with each other for resources, we know from lab studies that they share information and nutrients underground. Trees of the same species growing close together will sometimes fuse their roots and exchange materials. And seedlings of different species can share nutrients via mycorrhiza, the symbiotic fungi that grow alongside and between tree roots.
Now botanist Tamir Klein and his colleagues at the University of Basel in Switzerland have spotted this transfer in mature wild trees for the first time. And it turns out they share much more than anyone guessed.
Klein’s team was studying how spruce trees in a nearby forest in Switzerland would respond to higher levels of carbon dioxide in the atmosphere in the future. To do this, they sprayed CO2 with a particular mix of carbon isotopes, into the canopy for five years, and tracked how the trees used the carbon.
When they later tested the roots of neighbouring beech, larch and pine trees, they saw something unexpected. “To my surprise, we found the isotope signature in the other roots as well,” he says.
The trees were sharing a huge amount – around 40 per cent of the carbon in any given root came from a neighbouring tree.
This means that, in a single hectare of forest, the trees must be swapping around 280 kilograms of carbon a year, equivalent to 4 per cent of the forest’s total carbon uptake.
And it was a two-way street – carbon didn’t flow solely from trees with too much to those that needed more, but instead mixed freely back and forth.
Klein thinks that fungi are responsible for shuttling the carbon around. “The mycorrhiza need carbon for their own growth, and as a by-product are mixing it between the trees.”
Melanie Jones, a mycologist at the University of British Columbia in Kelowna, Canada, says she was surprised by the amount of carbon being moved. “That 40 per cent is a big number,” she says. The fact that it doesn’t follow a simple path from those that have it to those that don’t was also interesting, she adds. “That runs counter to what we thought before.”
Jones says this is good news for our understanding of how forests can respond to the stresses of climate change, like drought or new insect pests.
“If the fungi are getting carbon from multiple sources, they can still survive and continue to carry out their ecosystem functions if all the beech, for example, are wiped out by an insect,” she says. “And they’ll still be there for the beech if they ever recover.”
Journal reference: Science, DOI: 10.1126/science.aad6188