Right beneath our feet lies a world we barely notice. Most of us rarely touch soil, let alone think about it, yet our entire existence depends on what happens underground. As evolutionary ecologist Dr Justin Stewart tells RESET: “We know more about space and the depths of the ocean than we do about the ground beneath our feet.”
And this is even though a hidden parallel world exists there. If you examine soil under a microscope, you are very likely to find traces of fungi. A teaspoon of healthy soil can contain up to 100 metres of their fine filaments. These originate from complex underground fungal networks that span the planet and are among the oldest known forms of life. And the ability of these fungi to store large quantities of carbon over long periods of time makes them indispensable to our ecosystems.
An international research team has now investigated the global scale of these vast underground networks for the first time. To do so, the scientists combined soil samples with machine learning, satellite technology and a specially developed robot called Prince. The result is an incredible digital map of the world’s fungal networks. It is available online and is interactive, meaning that anyone can explore this unique system with just a few clicks.
Fluorescent fungal hyphae
The fungal filaments in the video that Stewart shows us during our conversation look like glowing cobwebs. They are hyphae; tube-shaped strands of fungal cells that are ten to 50 times thinner than a human hair. “These arbuscular mycorrhizal fungi evolved over 450 million years ago”, says Stewart. Back then, they enabled plants to make the transition from water to land by replacing their missing roots. In this way, they helped build entire ecosystems, whilst operating entirely underground: mycorrhizal fungi do not form fruiting bodies and therefore remain hidden from us humans.
Stewart is a member of the ‘Society for the Protection of Underground Networks’ (SPUN), an international organisation based in the USA. The team of scientists and experts shares a fascination with the magical underground world and has made it their mission to protect it. Together with Corentin Bisot from the Dutch AMOLF Institute for Biophysics, Stewart led the research project centred on the key question: How large is this global underground system? In June 2026, they published their findings in the scientific journal Science.
One thing was clear from the outset: this network plays a vital role in nature. Arbuscular mycorrhizal fungi engage in a mutually beneficial exchange with around 70 percent of the world’s plant species. They supply the plants with water and nutrients such as nitrogen and phosphorus, which they bind within their underground networks. In return, the plants send carbon to the fungi, which store it.
The special talent of mycorrhizal fungi lies not only in absorbing carbon, but also in how it is stored: “Because they are so long and thin, the hyphae can carry carbon so deep into the soil that it physically binds to minerals. Once this bond takes place, the carbon can remain there for hundreds to thousands of years,” says Stewart. For the climate, this provides highly effective natural protection: as long as the carbon remains bound in the soil, it cannot enter the atmosphere as a greenhouse gas.
In the video, the inside of the glowing webs can be seen in constant motion. Fluorescent particles flow through them: “These are the real-time movements of carbon,” Stewart explains. They are made visible thanks to a special team member of the research group: Prince, a robot built specifically for the project.
Mapping the subsurface
To grasp the scale of the underground network, the researchers analysed data from 16,000 soil samples collected by hundreds of scientists across more than 4,000 locations. These come from a wide variety of ecosystems—from forests and deserts to farmland. During the analysis, the team realised that the volume of data was sufficient to predict the global structures of these underground networks using satellite technology and machine learning. This sparked the idea not just to measure them, but to map and visualise them as well.
To achieve this, the AMOLF Institute developed the imaging robot Prince for laboratory use. There, researchers worked with Petri dishes split by a central barrier—with the plant on one side and the fungus on the other. They remained connected via the fungal hyphae, allowing nutrients and carbon to flow between them. Prince ultimately took high-resolution images of these Petri dishes, capturing more than 300,000 replicates of hyphae from various fungal and plant species. “This allowed us to extract the architecture of the networks,” says Stewart.
With this additional data, the team began developing a machine learning model. Its goal was to understand what determines fungal density in a given area. The researchers trained the model on factors such as land use, climate and vegetation. In doing so, they identified clear correlations: for example, the highest average density of arbuscular mycorrhizal fungi was found in wild grassland.
The team used these recognised patterns to predict hyphal density in regions where no data was available. “You can think of it like a grid of pixels. If you know what is in certain pixels, you can project that onto other pixels,” says Stewart. Of course, this does not mean that further research is no longer needed. On the contrary, future fieldwork aims to replace these estimates with local data.
From the Earth to the Sun—and back a billion times
110 quadrillion kilometres—that is how long the resulting network would be if you lined up every arbuscular mycorrhizal fungal hypha from the top 15 centimetres of soil. That is roughly equivalent to a billion times the distance from the Earth to the Sun. The researchers also calculated the biomass of this global system, arriving at around 300 million tonnes. That is approximately five times the weight of the entire human population.
What do you do with a finding like this? The answer is simple: it needs to reach as many people as possible to bring mycorrhizal fungi into the public consciousness. “Fungi deserve just as much attention as the ozone layer or plastic in the ocean,” says Stewart. They keep our ecosystems alive and are crucial allies in the fight against climate change.
Arbuscular mycorrhizal fungi alone sequester around four billion tonnes of carbon dioxide per year. If we include other species of mycorrhizal fungi that perform similar functions, they sequester a total of more than 13 billion tonnes annually. This corresponds to around 35 percent of global CO₂ emissions from fossil fuels.
Mushrooms are more versatile than you might think
Whether as a building material, a leather substitute or a battery – fungi are brimming with potential. RESET has previously highlighted some of their most astonishing applications:
Will fungal batteries be the energy source of the future?
Will the buildings of the future be made from fungi?
Fungi-Power: These fungi can replace leather
Fungi with an appetite for building rubble
SPUN is actively pushing for politicians and decision-makers to embrace this knowledge, ensuring that future nature and climate conservation measures also include fungi. Chile is leading the way in this regard, having legally protected fungi since 2013. This was made possible by the Fungi Foundation—a partner organization of SPUN—which has been advocating for their conservation in Chile since 2010. Under the motto “Flora, Fauna, Funga”, the organization campaigns to give fungi equal standing with plants and animals in environmental protection. The UN has also publicly called for the inclusion of this third “F”.
Protect the soil, protect the fungi
When we look around, we usually gaze straight ahead or look up towards space and the stars. Yet a fascinating world lies right beneath our feet. Beneath every square metre of soil, there are far more organisms than there are people on Earth. In fact, 59 percent of all species on Earth live entirely or partially in the soil. No other habitat is richer in species—not even the oceans.
“The soil is a fragile and precious ecosystem that we must study, value, and preserve,” says Stewart. Agriculture has a major impact on its quality. Data shows that large-scale agricultural use reduces the density of fungal networks by about half. This disrupts the nutrient cycle and reduces the amount of carbon that can be stored, making the soil as a whole less resilient.
Stichproben der Erde in der Mojave-Wüste Mycorrhizal fungi suffer particularly from the use of pesticides, as a study published in January 2026 revealed. 70 percent of European soils contain pesticide residues. Fungicides—active substances directed against fungi—are the most commonly used, accounting for 54 per cent. These suppress and push back fungal networks. In addition to agricultural land, pesticides are also found in forests and meadows. The researchers suspect that wind carries the chemicals across these areas.
At the same time, there are ways to increase fungal density and thereby support soil health—for example, through regenerative farming methods. How effectively mycorrhizal fungi establish themselves in arable soil depends heavily on how a field is managed: ploughing the soil less frequently preserves the fungi’s delicate network of hyphae. Crop rotation can also prove beneficial for soil fungi. Furthermore, moderate organic fertilisation has a more favourable impact than mineral fertilisers. If a healthy mycorrhizal network enriches the soil with more nutrients, the use of fertilisers can ideally be reduced.
Stewart’s vision for the future? “What I would like to see is the world’s first nature reserve for soil life,” says the scientist. “It could be a grassland in Kazakhstan or the Flint Hills prairie in Kansas. Above ground, it might look boring. But underground, you find one of the most complex habitats and a set of interactions of all life on Earth.”
