Beneath every step we take through a forest or meadow, a sprawling subterranean economy is at work. Fungi known as arbuscular mycorrhizae weave themselves into the roots of nearly all land plants, trading mineral nutrients for the sugars and lipids that plants produce through photosynthesis. For decades, ecologists have debated whether this network, often poetically called the “wood-wide web,” also shuffles carbon directly between different plant species. Proving that a green, photosynthetic plant siphons carbon from its neighbors via fungal pipelines has been exceptionally difficult, in part because the isotopic signatures of these fungi often mirror those of their hosts, obscuring the route of any transferred carbon. Now, a team of researchers in Japan has caught one unassuming flowering plant in the act, providing the clearest evidence yet that partial carbon theft via fungal networks is a real survival strategy in the arbuscular mycorrhizal world.
The plant at the center of this discovery is Gentiana squarrosa, a tiny herb that produces delicate blue flowers. It belongs to the gentian family, many members of which have long been suspected of supplementing their own photosynthesis with carbon shuttled in from other plants through shared mycorrhizal fungi — a lifestyle known as partial mycoheterotrophy. Full mycoheterotrophs, such as the ghostly, non-photosynthetic orchids of deeply shaded forests, are extreme specialists that have abandoned chlorophyll entirely, relying exclusively on fungi to deliver carbon compounds pilfered from surrounding trees. Partial mycoheterotrophy, however, is a more ambiguous middle ground: the plant still photosynthesizes, but it also taps into the communal fungal web for an extra subsidy. Until now, this mode of existence had been confirmed in only a handful of plant families that partner with ectomycorrhizal fungi, leaving a gaping question about whether it occurs in the far more widespread arbuscular mycorrhizal symbioses, which involve over seventy percent of all plant species.
The chief obstacle has been that arbuscular mycorrhizal fungi, unlike their ectomycorrhizal cousins, do not dramatically alter the ratio of carbon-13 to carbon-12 in the carbon they pass to plants, making isotopic detective work nearly impossible. To overcome this, Professor Masahide Yamato of Chiba University and his colleagues devised an elegant experiment that used the plants’ own photosynthetic machinery as a natural labeling system. They grew seedlings of G. squarrosa alongside either C₃ companion plants — which use a photosynthetic pathway that discriminates heavily against the heavier carbon-13 isotope — or C₄ companion plants, which naturally accumulate more carbon-13. If carbon were moving from the companion plants through the fungal web and into the gentian seedlings, the isotopic signature of the recipient would skew toward that of its donor.
The researchers constructed a U-shaped pot system in which a fine nylon mesh separated the root compartments of the companion plant and the G. squarrosa seedling. The mesh was sized to block the passage of roots but to freely permit the thread-like hyphae of arbuscular mycorrhizal fungi to penetrate and form a living bridge. In this way, any change in the gentian’s carbon-13 levels could only be attributed to fungal-mediated transfer. After a period of co-cultivation, the team harvested the shoots of the Gentiana seedlings and measured their isotopic composition with a mass spectrometer. The results were striking: seedlings coupled with C₄ companions consistently showed significantly higher carbon-13 enrichment than those paired with C₃ companions. “Specifically, if carbon transfer occurs through AM fungal connections, the carbon-13 isotope ratio should be higher in G. squarrosa seedlings grown with a C₄ companion plant than in those grown with a C₃ companion plant,” explained Professor Yamato. “That is exactly what we observed.”
Beyond the isotopic proof, the study uncovered a telling correlation between growth and carbon-13 levels among the C₄-paired plants. Seedlings that had pulled in more of the heavier isotope were also larger, suggesting that the hijacked carbon was not merely a trace signal but a meaningful nutritional supplement that boosted growth under the experimental conditions. This implies that partial mycoheterotrophy can confer a genuine ecological advantage, perhaps particularly in environments where light is limiting and a plant’s own photosynthetic machinery cannot keep pace with its metabolic demands.
The implications ripple far beyond a single species of gentian. Arbuscular mycorrhizal fungi are the most widespread mycorrhizal partners on the planet, linking the roots of grasses, herbs, and trees in virtually every terrestrial ecosystem. If the capacity to draw carbon from neighbors through these networks is present in other plant lineages, it could fundamentally reshape how we understand nutrient dynamics in ecosystems. Instead of a tidy model where every plant is an independent carbon factory, forests and grasslands might function more like a hybrid power grid, with some plants acting as net producers and others as occasional consumers, all mediated by the fungal internet beneath our feet.
Professor Yamato believes the experimental approach itself is as important as the discovery. “The U-shaped pot cultivation experimental system developed in this study will enable us to verify the presence or absence of carbon transfer between plants via AM fungi in various plant species,” he said. “If confirmed in diverse plants, the hyphal network may not simply be a pathway for nutrient absorption but may also function as a site for ‘energy distribution’ where carbon compounds move between plants.” The team plans to apply the method to a wider range of species to map the scope of this cryptic carbon economy. Their findings, published in the journal Mycorrhiza, crack open a door that ecologists have been gently knocking at for years, and what lies beyond could transform the way we see plant communities — not as a set of silent competitors but as interconnected participants in a web of shared vitality.
Subject of Research: Partial mycoheterotrophy in the arbuscular mycorrhizal plant Gentiana squarrosa demonstrated via fungal-mediated carbon transfer between C₃ and C₄ companion plants.
Article Title: Partial mycoheterotrophy in the arbuscular mycorrhizal Gentiana squarrosa (Gentianaceae) demonstrated by coculture assays using C₃ and C₄ plants
News Publication Date: 28 May 2026
Web References: 10.1007/s00572-026-01271-6
References: Yamato, M., Sasuga, M., Shimabukuro, K., Kusakabe, R., & Suetsugu, K. (2026). Mycorrhiza, 36, DOI: 10.1007/s00572-026-01271-6.
Image Credits: Professor Masahide Yamato, Chiba University, Japan.
