Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests

Karst, Justine; Jones, Melanie D.; Hoeksema, Jason D.

doi:10.1038/s41559-023-01986-1

Cited by 59 publications

(44 citation statements)

References 101 publications

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“…The possibility of overstory trees facilitating seedling growth via CMNs would have far‐reaching consequences within and beyond the realm of scientific research. The field is attracting a wide and diverse readership and scientific claims are being further disseminated by non‐peer‐reviewed media (Karst et al ., 2023). Based on the methodological caveats of studies on CMN‐mediated resource sharing between trees, we argue that interpretations of the isotopic evidence should be revised.…”

Section: Discussionmentioning

confidence: 99%

“…However, a recent meta‐analysis (Karst et al ., 2023) showed a growing tendency toward unsupported citations in the scientific literature in favor of a beneficial view of CMNs in forest ecosystems. Claims in favor of the mother tree concept have been controversial in the scientific community (Robinson & Fitter, 1999; Booth & Hoeksema, 2010; Högberg & Högberg, 2022).…”

Section: Introductionmentioning

confidence: 99%

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Re‐examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks

et al. 2023

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Seminal scientific papers positing that mycorrhizal fungal networks can distribute carbon (C) among plants have stimulated a popular narrative that overstory trees, or 'mother trees', support the growth of seedlings in this way. This narrative has far-reaching implications for our understanding of forest ecology and has been controversial in the scientific community. We review the current understanding of ectomycorrhizal C metabolism and observations on forest regeneration that make the mother tree narrative debatable. We then reexamine data and conclusions from publications that underlie the mother tree hypothesis. Isotopic labeling methods are uniquely suited for studying element fluxes through ecosystems, but the complexity of mycorrhizal symbiosis, low detection limits, and small carbon discrimination in biological processes can cause researchers to make important inferences based on miniscule shifts in isotopic abundance, which can be misleading. We conclude that evidence of a significant net C transfer via common mycorrhizal networks that benefits the recipients is still lacking. Furthermore, a role for fungi as a C pipeline between trees is difficult to reconcile with any adaptive advantages for the fungi. Finally, the hypothesis is neither supported by boreal forest regeneration patterns nor consistent with the understanding of physiological mechanisms controlling mycorrhizal symbiosis.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Re‐examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks

et al. 2023

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“…Whether mycorrhizal colonization intensity per se exerts a control on root exudation and root litter decomposition remains contradictory, though (Meier et al ., 2013; Trap et al ., 2017; Argiroff et al ., 2022). Furthermore, it has been debated whether common mycorrhizal network between roots of multiple plants are used to shuttle C from one plant to another, but the knowledge is presently still too sparse and unsettled to speculate on any control by the network on the root C release (Karst et al ., 2023).…”

Section: Discussionmentioning

confidence: 99%

“…The copyright holder for this preprint this version posted March 23, 2023. ; https://doi.org/10. 1101/2023.03.19.533308 doi: bioRxiv preprint al., 2017. In addition, they rely on far-reaching rhizomorphs (when associated with ECM basidiomycetes) and many thin fungal hyphae for soil exploration and exploitation of soil micropores.…”

Section: Introductionmentioning

confidence: 99%

A synthesis on the role of mycorrhizal fungal traits for understanding forest tree functions

Khokon

Meier

2023

Preprint

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Nearly all tree species associate with mycorrhizal fungi, which promote their hosts in soil resource acquisition and influence the nutrient economy of the ecosystem. Yet despite the fundamentality of this symbiotic interaction, our understanding how fungal traits relate to host traits is still in its infancy. We compiled a unique mycorrhizal fungal trait database, which sets fungal traits in relation to host functions of forest trees in the categories resource acquisition, plant productivity, and carbon (C) release. Based on meta-analysis, we demonstrate current strengths and gaps of knowledge with respect to tree species and spatial coverage, and fungal trait-tree function relationships. Most studies demonstrate a positive influence of the fungal community assembly, host-symbiont interactions, and soil exploration on resource acquisition and plant production. By contrast, the fungal community assembly related negatively to root C exudation (with low certainty). The influence of mycorrhizal colonization or soil exploration on host C release remains unclear. We conclude that the fungal effect trait category 'soil exploration' and the tree response trait category 'C release' remain major avenues for future research, which should advance from lab-measurements of soft traits and increasingly focus on mycorrhizal traits with the widest importance in ecosystem functioning.

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“…Among proponents of this theory is Suzanne Simard from the University of British Columbia, who is now pursuing these ideas in the Mother Tree Project (https://mothertreeproject.org/), but she did not respond to requests for comment. Among the critics is Dan Bebber, Co-Director of Global Engagement for Biosciences at the University of Exeter, who referred to a recent paper showing that there is no evidence for this idea, only a positive citation bias (Karst et al, 2023). This paper refers to common mycorrhizal networks (CMNs) that connect the roots of multiple plants of the same or different species below ground and expresses concern that bias towards their positive effects in the scientific literature has stoked the popular idea of trees engaging in sophisticated interactions over the plant/fungal networks.…”

Section: Tapping Into the Networkmentioning

confidence: 99%

The fungal grid

Hunter¹

2023

EMBO Reports

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Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests

Cited by 59 publications

References 101 publications

Re‐examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks

Re‐examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks

A synthesis on the role of mycorrhizal fungal traits for understanding forest tree functions

The fungal grid

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