First global map of mycorrhizal fungi reveals the scale of Earth’s underground networks
Researchers published the first global map of mycorrhizal fungi in Science on 11 June 2026, estimating 110 quadrillion km of underground networks.
Photo by Nothing Ahead on Pexels
An international research team has published the first global map of mycorrhizal fungi, estimating the distribution and mass of the arbuscular mycorrhizal (AM) fungal networks that thread through the planet’s topsoil. The study, “Global density and biomass of arbuscular mycorrhizal fungal networks,” appeared in the journal “Science” on 11 June 2026, led by the Society for the Protection of Underground Networks (SPUN) with research institute AMOLF and university partners. The maps put the total length of these networks at about 110 quadrillion kilometres — close to a billion times the distance from Earth to the Sun.
The work was released with an interactive visualisation, the Mycorrhizal Infrastructure Map, and a downloadable dataset that governments and researchers can use to track where these fungal systems are intact and where they are under pressure.
What the global map of mycorrhizal fungi shows
Arbuscular mycorrhizal fungi form symbiotic trade relationships with roughly 70% of plant species, supplying nutrients and water in exchange for plant carbon. The team estimates the networks hold about 300 megatons of carbon — four to six times the combined mass of all living humans — and draw an estimated 4 billion tons of CO2-equivalent into soils each year, which the authors equate to about 11% of human-related carbon-dioxide emissions.
The maps also locate the densest networks. Grassland ecosystems hold an estimated 40% of Earth’s AM fungal infrastructure, with exceptionally high predicted density in the flooded grasslands of South Sudan, the Everglades in Florida, and the Tibetan plateau. Large-scale agricultural croplands, by contrast, are predicted to carry roughly 50% lower network density than wild ecosystems.
| Measure | Value | Source |
|---|---|---|
| Total AM hyphal length in global topsoils | ~110 quadrillion km | Stewart et al., “Science”, 2026 |
| Total network biomass | ~300 megatons of carbon | Stewart et al., “Science”, 2026 |
| Carbon drawn into soils each year | ~4 billion tons CO2e (~11% of human CO2 emissions) | Stewart et al., “Science”, 2026 |
| Plant species in symbiosis with AM fungi | ~70% | Stewart et al., “Science”, 2026 |
| Phosphorus supplied to host plants in healthy soils | >80% | Stewart et al., “Science”, 2026 |
| Soil cores analysed | 16,000+ | Stewart et al., “Science”, 2026 |
| Living hyphae imaged to calibrate models | 300,000+ | Stewart et al., “Science”, 2026 |
| AM biodiversity hotspots outside protected areas | 95% | SPUN, “Nature”, 2025 |
Source: Stewart et al., “Global density and biomass of arbuscular mycorrhizal fungal networks”, “Science”, 2026 (SPUN); protected-areas figure from SPUN’s 2025 “Nature” analysis.
“It is hard to overstate the importance and enormity of these fungi,” said lead author Dr Justin Stewart of SPUN. “There could be up to 10 meters (32 feet) of mycorrhizal network in just a teaspoon of soil.”
How the researchers mapped the fungal networks
The team assembled density data from more than 16,000 soil cores collected across ecosystems ranging from deserts and tundra to forests. They built machine-learning models to predict network density in unsampled regions, then calibrated those models against robotic imaging of more than 300,000 living AM fungal hyphae grown in the laboratory, in collaboration with the Physics of Behavior group at AMOLF. Estimates were calculated for every square kilometre of terrestrial land, excluding ice caps and areas with too little data to support a prediction.
“With the emergence of new technologies in high-resolution imaging, machine-learning and robotics, we are starting to reveal what has long been hidden under our feet,” said co-lead author Dr Corentin Bisot, an AMOLF biophysicist. The visualisation was built with data-visualisation designer Moritz Stefaner, marking the first time the fungal infrastructure has been shown at this scale and resolution.
Why mycorrhizal fungi matter for climate and farming
The networks act as one of the Earth’s circulatory systems, moving carbon, water, and nutrients through soil. In healthy soils they can increase the foraging area of plant roots by up to 100 times while providing more than 80% of a plant’s phosphorus. That role connects the maps to soil-carbon strategies the site has tracked, including carbon removal through enhanced rock weathering and biochar application, where soil fungi help break down silicate minerals.
The cropland finding carries the clearest land-use signal. Densities under large-scale agriculture are predicted to be about half those of wild ecosystems, and the authors note that thinner networks may reduce a soil’s ability to store carbon, cycle nutrients, and withstand stress — though they state that more work is needed to connect specific farming practices to mycorrhizal health. The result adds weight to soil-focused approaches such as regenerative agriculture as a route to sustainable crops.
The study also restates a conservation gap. Grasslands hold about 40% of the world’s AM fungal biomass yet are among the least protected ecosystems, and SPUN reported in 2025 that 95% of AM fungal biodiversity hotspots lie outside protected areas. “Fungi have been ignored in climate and conservation for too long,” said Dr Toby Kiers, SPUN’s Executive Director and a 2025 MacArthur Fellow and Tyler Prize winner. “Now is the time to change that trajectory.” Co-author Dr Merlin Sheldrake said the work “is an exciting step towards understanding how this planetary circulatory system operates.”
About the Society for the Protection of Underground Networks
SPUN was founded in 2021 as a non-profit scientific research organisation with the stated mission of mapping and protecting Earth’s mycorrhizal networks, working with researchers and local communities to bring underground ecosystems into conservation and climate planning. In 2025 several of the same authors published analyses in “Nature” of underground mycorrhizal diversity, paired with a digital tool, the Underground Atlas, to flag predicted biodiversity hotspots; a related “Nature” study measured carbon and nutrient flows inside the networks. The new “Science” paper extends that work from diversity to physical scale, mapping the density and mass of AM networks worldwide. The organisation says the underlying data are now downloadable so decision-makers can begin monitoring the health of the fungal systems the maps reveal. The research was supported by funders including the Grantham Foundation, the Paul G. Allen Family Foundation, the Bezos Earth Fund, the Schmidt Family Foundation, the European Research Council, and the Natural Environment Research Council.
Sources: Science; EurekAlert! / SPUN; University of Sheffield; Mongabay
Featured image: photo by Nothing Ahead on Pexels (free Pexels license).
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I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.
