Do forest trees really “speak” through underground fungi?

Forest mushrooms mushrooms

scientists in the journal Natural Ecology & Evolution challenge three widely held beliefs regarding the capabilities of mycorrhizal networks (CMNs), which are underground fungi that connect the roots of multiple plants.

The University of Alberta expert challenges popular claims about the ‘Wood-Wide Web’.

The idea that forest trees can “talk” to one another, sharing resources with their seedlings – and even protecting them – through a connecting underground web of delicate fungal filaments stimulates the imagination.

The concept is so intriguing that it’s taken root in popular media — even the popular Apple TV show Ted Lasso — and has been dubbed the “Wood-Wide Web,” but the science behind these ideas is unproven, warns an expert on the University of Alberta Justin Karst.

In a peer-reviewed article published in the journal today (February 13). Natural Ecology & Evolution Also sharing their personal point of view, Karst and two colleagues dispute three popular claims about the abilities of underground fungi, known as shared mycorrhizal networks, or CMNs, that connect the roots of multiple plants underground. Fungi are living organisms such as molds, yeasts and fungi.

“It’s great that CMN research has sparked interest in forest fungi, but it’s important that the public understands that many popular ideas are ahead of science,” says Karst, associate professor in the Faculty of Agricultural, Life and Environmental Sciences of the U of A.

Justin Folios

Ecologist Justine Karst is co-authoring a new perspective paper that contradicts claims that underground fungal networks allow trees to “talk” to each other and share resources with seedlings. Photo credit: University of Alberta

Although the existence of CMNs has been scientifically proven, there is no clear evidence that they offer any benefits to trees and their seedlings, the researchers suggest.

To assess the popular claims, Karst and co-authors Melanie Jones of the University of British Columbia Okanagan and Jason Hoeksema of the University of Mississippi reviewed evidence from existing field studies.

They found that one of the claims that CMNs are widespread in forests is not supported by enough scientific evidence. Not enough is known about the CMN structure and its function in the field “because too few forests are mapped”.

The second claim that resources such as nutrients are transferred from adult trees to seedlings by CMNs and that they promote survival and growth was also found questionable.

A review of 26 studies, including one in which Karst is a co-author, found that while resources can be transferred from trees to the subsurface, CMNs do not necessarily effect this flow and seedlings do not typically benefit from access to CMN. Overall, their review found roughly equal evidence that association with a CMN would improve or hinder seedlings, with neutral effects being the most commonly reported.

The third claim that adult trees preferentially send resources or “warning signals” of insect damage to young trees through CMNs is not supported by a single peer-reviewed published field study, Karst and her co-authors note.

The researchers say that exaggerated information can shape and distort the public narrative about CMNs, and this in turn could affect the way forests are managed.

“Biasing the science on CMNs in forests is a problem because sound science is critical to making decisions about how forests are managed. It is premature to base forest practices and policies on CMNs per se without further evidence. And failing to recognize misinformation can erode public confidence in science.”

Reference: “Positive citation bias and overinterpreted results lead to misinformation about shared mycorrhizal networks in forests” by Justine Karst, Melanie D. Jones and Jason D. Hoeksema, February 13, 2023, Natural Ecology & Evolution.
DOI: 10.1038/s41559-023-01986-1

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