PHOTO: Matteo Grando/Unsplash
PHOTO: Matteo Grando/Unsplash

EXPERT REACTION: The last of fungal networks

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Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

That trees can “talk” to each other through underground fungal networks is a notion that’s gained traction in recent years, but North American researchers argue the current research just doesn’t back it up. In a perspective piece, they also say citation bias and the over-interpretation of results could be leading to a misinterpretation of the ‘wood-wide web’ and its role in forests.

Journal/conference: Nature Ecology & Evolution

Link to research (DOI): 10.1038/s41559-023-01986-1

Organisation/s: University of Alberta, Canada; University of British Columbia, Canada; University of Mississippi, USA

Funder: n/a

Media release

From: Springer Nature

Citation bias and the over-interpretation of results could be leading to a misinterpretation of common mycorrhizal networks — the ‘wood-wide web’— and their role in forests, a Perspective published in Nature Ecology & Evolution argues. The findings, based on literature reviews and citation analysis, suggest that three common claims about the networks of mycorrhizal fungi are insufficiently supported by scientific evidence.

Many plant species, including forest trees, benefit from partnerships with mycorrhizal fungi, which live on plants’ roots and spread in vast networks under the forest floor. That trees can communicate with each other through these fungal networks, for example by sending warning signals to their offspring when damaged, has gained recent traction in the popular media and scientific literature. However, the role of these networks has been debated.

Justine Karst and colleagues analysed evidence for three common claims about common mycorrhizal networks (CMNs) from the media and scientific literature. The authors find that claims that CMNs are widespread in forests and that they transfer resources and increase seedling performance are insufficiently supported because the results from field studies vary, have alternative explanations or are too limited to support generalizations. They also find that claims that older trees communicate with offspring through CMNs are not supported by any peer-reviewed or published evidence. To examine citations, the authors looked at how 593 papers on CMN structure and 1,083 papers on CMN function referenced findings from 18 early influential papers. They found citations making unsupported statements have risen to 25% for CMN structure and almost 50% for CMN function, and also document a bias toward citing positive effects.

The authors conclude that claims about the positive effects of CMNs are disconnected from the available evidence. They indicate that further research is needed to explore these networks.

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Peter Buchanan, Mycologist / Science Team Leader, Manaaki Whenua – Landcare Research, Auckland

"The ‘wood-wide web’ is a catchy phrase that appropriately sparked public and media interest in the hidden complexity of life in soil. It helped awareness and new understanding of how plants and their mycorrhizal (‘fungus-root’) fungi are intimately connected.  One might use a crude analogy of a plumbing system under a town that provides essential services and operates just fine until there is disruption of some kind – Cyclone Gabrielle is our most recent example of our need to understand and protect what lies beneath.  That’s not to suggest that the massive ‘mycelial’ network of fungal thread-like cells that connect with plant roots are themselves simply pipes; they are much more complex than that. Also relevant is the term ‘Te Ao Mārama’ based on whakapapa and emphasising the interconnectedness of life.

"In evolutionary time, when plants from the oceans first colonised the land, fossil records show that fungi were already present. Plants formed functioning relationships with fungi that have persisted through 100s of millions of years since. They are the norm today for most plants in natural ecosystems. Turning it around from a prevailing plant-centric view, fungi have enabled the successful evolution and diversification of plants. Fungi even enabled plants without leaves to develop; these plants get their carbon and nutrients from associated mycorrhizal fungi for all or part of their life cycles. Such associated fungi are further connected to leaf-bearing plants from which they gain their essential carbon.   

"The authors of this Nature paper cite examples of misinformation about mycorrhizal relationships, and are particularly concerned about the impact on forest management practices. I support that concern. Greatly increased research is justified to better understand the functioning of mycorrhizal relationships across many more fungus-plant partnerships and forest types. Research on the whole ecosystem (flora, fauna, AND fungi – not to mention unicellular life forms) is relevant to achieve evidence-based forest management and improved understanding of plant health and nutrition in both our native ecosystems and our managed forests.

"A popular extension of the wood-wide web is the suggestion that trees talk to each other and cooperate together through their connecting mycorrhizal fungi. This is another catchy concept that appears to me to push the boundaries way beyond the supporting science. I concur with Kathryn Flinn, writing in Scientific American in 2021: the suggestion that trees are like communicating humans or other animals is both misleading and unnecessary. Our need to understand and conserve the incredible complexity of life present in the soils of our forests, wetlands, and other natural environments is sufficient in itself - without personification and a human-centric approach. Let’s respect and understand the fungi and the plants on their own terms as totally different but intimately interactive co-inhabitants of their (and our) planet."  

Last updated: 17 Feb 2023 9:04am
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