The study, published in Science, focuses on arbuscular mycorrhizal fungi, a group of fungi that form partnerships with most plants on Earth. Alongside the research, scientists released an interactive visualization that allows users to explore the remarkable scale of this hidden underground infrastructure. The maps are expected to help researchers and policymakers identify areas where these fungal networks are thriving and where they may be under threat.

Among the study's key findings:

• Global topsoils contain an estimated ~110 quadrillion kilometers (~68 quadrillion miles) of arbuscular mycorrhizal fungal network, made up of thread-like structures called hyphae. That distance is almost a billion times the distance from the Earth to the Sun.
• Grasslands contain roughly ~40% of Earth's arbuscular mycorrhizal fungal infrastructure. Particularly dense networks are predicted in the flooded grasslands of South Sudan, the Everglades in Florida, and the Tibetan plateau.
• AM fungal networks move an estimated ~4 billion tons of CO2e into soils every year (equivalent to 11% of all human-related carbon-dioxide emissions).
• Large agricultural croplands are predicted to have about ~50% lower network densities on average. Researchers caution that less dense fungal networks could reduce a soil's ability to store carbon, cycle nutrients, and withstand environmental stress.

The Hidden Partnerships Supporting Plant Life

Arbuscular mycorrhizal fungi, commonly called AM fungi, form mutually beneficial relationships with approximately ~70% of plant species worldwide. Plants provide the fungi with carbon produced through photosynthesis, while the fungi supply plants with nutrients and water.

These underground networks function as living infrastructure that helps sustain ecosystems and move carbon into the ground. In 2025, researchers published a global analysis of underground mycorrhizal fungal diversity in Nature and launched a digital platform called the Underground Atlas to help identify likely biodiversity hotspots beneath the surface. Until now, however, scientists had not attempted to estimate and map the physical density and worldwide distribution of AM fungal networks themselves.

Mapping 110 Quadrillion Kilometers of Fungal Networks

To build the new maps, researchers compiled measurements from more than 16,000 soil cores collected around the world. They then used machine-learning models that incorporated environmental data from deserts, tundra, forests, and other ecosystems to predict fungal network density in regions where direct measurements were unavailable.

Working with the Physics of Behavior group at the AMOLF research institute, the team also used robotic imaging to analyze more than 300,000 living AM fungal hyphae grown in laboratory conditions. Combining all of these data sources allowed researchers to estimate both the total length and mass of the global network.

Their analysis suggests that AM fungal networks extend for approximately ~110 quadrillion kilometers and contain roughly ~300 megatons of carbon (4-6x the mass of all living humans).

"It is hard to overstate the importance and enormity of these fungi," said lead author Dr. Justin Stewart, with the Society for the Protection of Underground Networks (SPUN). "There could be up to 10 meters (32 feet) of mycorrhizal network in just a teaspoon of soil."

Earth's Underground Circulatory System

Scientists often describe mycorrhizal networks as one of Earth's circulatory systems because they transport carbon, nutrients, and water throughout underground ecosystems.

In healthy soils, these fungal networks can expand the effective foraging area of plant roots by up to 100 times and provide > 80 percent of a plant's phosphorous needs.

"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. "We are learning how the complex bodies of network-forming fungi transport nutrients and help regulate the climate."

A New Global Fungal Infrastructure Map

To help visualize the results, the researchers collaborated with award-winning data visualization designer Moritz Stefaner to create the Mycorrhizal Infrastructure Map.

The project offers the most detailed global view yet of Earth's fungal infrastructure. Estimates were calculated for every 1km² of terrestrial land, excluding ice caps and regions where data were insufficient for reliable predictions.

The data behind the maps are publicly available, giving governments and other decision-makers new tools for monitoring the health of underground fungal communities.

The work builds on previous research published by several of the same authors in Nature. That study examined how mycorrhizal fungi and plants create highly efficient systems for exchanging carbon and nutrients. Researchers measured carbon movement through these living networks at speeds reaching 120 um/sec (if one was inside the network, these speeds would feel like ~400km/hr). The new study extends that work by exploring how these flows operate at a planetary scale.

Threats to Underground Fungal Ecosystems

The researchers also identified areas of concern.

Network densities in croplands are predicted to be about half those found in wild ecosystems. At the same time, wild grasslands contain roughly ~40% of the world's arbuscular mycorrhizal biomass.

Despite their importance, grasslands remain among the least protected ecosystems on Earth and are being converted to agricultural land four times faster than forests.

These findings support previous SPUN research showing that 95% of biodiversity hotspots for arbuscular mycorrhizal fungi lie outside protected areas.

For evolutionary biologist Dr. Toby Kiers, Executive Director of SPUN, the growing body of evidence highlights the need to include fungi in climate and conservation planning.

"Fungi have been ignored in climate and conservation for too long. Now is the time to change that trajectory."

Kiers was recently named a MacArthur Fellow and received the Tyler Prize, often called the "Nobel Prize for the Environment," for her work on plant-fungal relationships.

What Scientists Still Don't Know

"Mycorrhizal fungi have shaped life on earth for hundreds of millions of years, but we still understand too little about how the infrastructure of these living transport systems is distributed across the planet," added co-author and biologist Dr. Merlin Sheldrake. "This study is an exciting step towards understanding how this planetary circulatory system operates and suggests ways that we can better work with fungi to help address many of the unfolding challenges of our times, from food security to climate change."

While the new maps reveal the extraordinary scale of Earth's underground fungal networks, they also highlight major gaps in scientific knowledge. Large regions of the world remain unsampled, providing a roadmap for future research into one of the planet's most important and least visible ecosystems.