Beneath every forest, meadow and farm field lies a fungal web so vast that scientists have only now managed to measure it in full. Researchers have released the first global map of arbuscular mycorrhizal fungi, the underground network that quietly keeps roughly 70 percent of the planet's plant species alive.
A Partnership Written Into the Soil
These fungi, known as AM fungi, spread through soil using microscopic threads called hyphae. Instead of competing with plants, they attach themselves to roots and trade services, the fungi hand over water and mineral nutrients they have drawn from the soil, and in return the plant shares carbon it has captured through photosynthesis. It is a partnership that has apparently helped shape ecosystems for hundreds of millions of years, yet until now nobody had measured how much of it actually exists or where it is concentrated.
A study published in Nature last year had already mapped how the diversity of these underground fungal communities varies from place to place. But diversity is not the same as density or scale, and no research before this new study had tried to quantify how much of this hidden network exists worldwide.
Building the First Global Map
To fill that gap, researchers pulled together data from 322 earlier studies and combined it with 16,000 soil samples gathered from ecosystems around the world. Feeding all of that into machine learning models, along with advanced imaging techniques, allowed the team to estimate both how far the network stretches and how much biomass it holds.
Coauthor Corentin Bisot said, With the advent of new technologies in high-resolution imaging, machine learning, and robotics, we are beginning to reveal what has long remained hidden beneath our feet. We are discovering how the complex network-forming structures of fungi transport nutrients and help regulate the climate.
A Network Bigger Than the Imagination Allows
The scale that emerged from the data is hard to grasp. The team's estimate puts the total length of this underground fungal network at approximately 110 quadrillion kilometers, and its biomass at about 300 megatons of carbon, which the researchers say is equivalent to roughly four to six times the combined mass of every human being alive.
The network also does climate work, it moves the equivalent of around 4 billion metric tons of carbon dioxide into the soil every year, a figure the study says amounts to close to 11 percent of humanity's annual carbon dioxide emissions.
Lead author Justin Stewart, of the Society for the Protection of Underground Networks, put the density into everyday terms, It is difficult to overstate the importance and sheer scale of these fungi. A single teaspoon of soil can contain up to 10 meters of mycorrhizal network.
Farms Are Thinning Out the Network
The study also carries a warning. It found that the density of these fungal networks in agricultural soil is only about half of what is found in natural ecosystems. That matters because grasslands, which hold an estimated 40 percent of the world's arbuscular mycorrhizal biomass, are among the least protected ecosystems on the planet, and they are being converted into farmland four times faster than forests are.
According to the researchers, a thinner fungal network means the soil becomes less able to store carbon and recycle nutrients, weakening one of the planet's quieter climate defenses.
What Comes Next
Coauthor Merlin Sheldrake framed the findings as a starting point rather than a conclusion, Mycorrhizal fungi have shaped life on Earth for hundreds of millions of years, yet we still know remarkably little about how the infrastructure of these living transport systems is distributed across the planet. This study marks an exciting step toward understanding how this planetary circulatory system functions, and it points to ways we can work more effectively with fungi to address many of the defining challenges of our time, from food security to climate change.
