Nearly All Plants Depend on Tiny Underground Fungi. The Microbes’ Vast Global Networks Were Just Mapped for the First Time

If lined up end to end, the thin, tubular threads that make up the arbuscular mycorrhizal fungal networks in Earth’s topsoil could stretch between our planet and the sun almost one billion times

Margherita Bassi | Daily Correspondent

June 18, 2026 10:00 a.m.

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Around 500 million years ago, plants started transitioning from water to land. These early terrestrial greens had no roots, however, so they partnered with tiny fungi called mycorrhizae to suck up nutrients and water from the dirt.

These underground allies likely helped plants eventually take over Earth’s lands, and today, the mutually beneficial relationship aids up to 90 percent of plant species.

Now, scientists have mapped the worldwide distribution of the most common type of mycorrhizae, called arbuscular mycorrhizal (AM) fungi. The findings, described in a study published June 11 in the journal Science, reveal that global topsoil hosts around 68 quadrillion miles of AM fungal networks—equal to nearly one billion times the distance between Earth and the sun. The work highlights a largely overlooked group of organisms that play crucial roles in supporting ecosystems and stabilizing the climate.     

“We’re excited about the number … because it just gives some sort of sense of the magnitude, the scale of what we’re looking at,” says study co-author Toby Kiers, an evolutionary biologist at Vrije Universiteit Amsterdam and executive director of the Society for the Protection of Underground Networks (SPUN), to the New York Times’ Emily Anthes. “But to me, what’s more exciting is not just giving it a length but actually putting it on a map and being able to see these patterns.”

AM fungi live on and in plant roots, where they absorb some of the plant cells’ carbon, an ingredient crucial to the fungi’s survival. Taking in the element will cause a fungus to shoot out tubular threads—called hyphae—that are a fraction of the width of a human hair, lead author Justin Stewart, an evolutionary ecologist at SPUN, tells National Geographic’s Bethany Brookshire. “They go deep into soils and extract nutrients, such as nitrogen and phosphorus, and they trade it back to the plant.”

By transporting water, nutrients and carbon throughout ecosystems, AM fungal networks support a significant amount of Earth’s life. They also help draw planet-warming carbon dioxide out of the atmosphere.

For the study, Stewart, Kiers and their colleagues gathered previously published data from more than 16,000 soil samples across the planet. Then, they developed a computer model that used machine learning to estimate the density of hyphae in unsampled areas, considering factors such as climate and vegetation, although it couldn’t come up with predictions for areas with too little soil data, like ice caps.  

Analyses revealed that the Earth’s quadrillions of miles of AM fungi contain around 330 million U.S. tons of carbon—roughly four to six times the carbon in all currently living humans. What’s more, the team estimates that every year, the fungi move the equivalent of about 4.4 billion U.S. tons of carbon dioxide into soils. That’s equal to around 11 percent of the carbon dioxide produced by human activity.

“It is hard to overstate the importance and enormity of these fungi,” Stewart says in a statement. “There could be up to 10 meters (32 feet) of mycorrhizal network in just a teaspoon of soil.”

The new research is “seminal,” Edouard Evangelisti, a plant scientist at Côte d’Azur University in France who was not involved in the research, tells Live Science’s Sophie Berdugo. It “makes part of the invisible visible.”

Anne Pringle, a mycologist at the University of Wisconsin, Madison, agrees. The study is “really interesting and adds a lot of information,” says Pringle, who was not involved in the study, to National Geographic. “A lot of it fills a rather large knowledge gap.”

The map also provides a glimpse into how human activity might affect AM fungi spread. Croplands have around half the fungal density of wild ecosystems, the team estimates. Additionally, roughly 40 percent of the planet’s AM biomass is in wild grasslands, including those in South Sudan, the Tibetan Plateau and the Florida Everglades, but they’re some of the least protected ecosystems on the planet. A study published in February in the Proceedings of the National Academy of Science estimates that non-forest ecosystems, including grasslands and wetlands, are converted into pasture and croplands four times as often as forests.

More research is needed to understand how particular farming practices might impact mycorrhizal health. But scientists suspect that soil with less dense AM fungal networks might have reduced capacity for cycling nutrients, resisting stress and storing carbon.

“I hope this builds into the conversation for their protection because wild grasslands are going away quite quickly,” Stewart tells Live Science. “These are areas that people are really ripping up because it’s much easier to rip up a grass than it is to rip up a tree.”

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.