Research team led by the University of Göttingen investigates carbon transport from the tree to the root fungus
The idea that trees "communicate" with each other via underground fungal networks - the so-called "Wood Wide Web" - has captured the imagination of many people. Books and documentaries have popularized the concept of trees supposedly exchanging nutrients with each other through these networks. However, a new study led by the University of Göttingen suggests that the reality may be somewhat more nuanced. The researchers found that young beech trees can transfer carbon to nearby "ectomycorrhizal fungi" - a type of fungus that grows on and together with the tree roots in a symbiotic relationship - but not to other trees. These fungi form complex underground connections with tree roots and it has been suggested that they could also connect trees and allow for a mutual exchange of nutrients. However, the latest research raises questions about how much exchange actually takes place. The results were published in the journal New Phytologist.
To track the movement of carbon, the scientists used isotope labeling. They supplied a young "donor" beech tree with CO2 enriched with a heavier carbon isotope (known as carbon-13) and waited five days to give the tree time to absorb carbon-13 and transfer it to its roots. They then measured the carbon in the roots, stems and leaves of a nearby potential "recipient" tree. Ectomycorrhizal roots, the roots that are symbiotically associated with the fungi, were of particular interest to the researchers. Using a surgical procedure, they separated the plant tissue from the fungus-colonized tissue of the root tips. They found that carbon-13, the marker for donor-derived carbon, was only present in the fungus-colonized tissue and not in the rest of the roots of the recipient tree. The research team repeated the experiment on Douglas fir trees and again found that carbon-13 was only present in the fungus-colonized tissue, albeit in lower quantities in this tree species.
"The results fuel a long-standing debate in ecology: Are trees really connected in a cooperative way?" says postdoctoral researcher Dr. Michela Audisio from the Department of Forest Botany and Tree Physiology at the University of Göttingen. She adds: ,,It is hard to imagine that ectomycorrhizal fungi would disinterestedly transfer carbon from one tree to another. But it is probably beneficial for the fungi to have access to multiple carbon sources, especially when they are under environmental stress". The researchers found that the ectomycorrhizal roots of Douglas fir, a non-native tree species, took up slightly less of the labeled carbon than those of European beech, which is native to our country. "This could mean that ectomycorrhizal fungi are less abundant in forests mixed with Douglas fir, possibly affecting the forest carbon cycle," says Audisio.
The study was part of the GRK 2300 "Enrico" project at the University of Göttingen and was funded by the German Research Foundation (DFG).
Original publication: Audisio M, et al. "Ectomycorrhizal fungi of Douglas-fir retain newly assimilated carbon derived from neighboring European beech", New Phytologist 2024. doi: doi.org/10.1111/nph.19943
