Mycorrhizal fungal networks weigh 5x all humans

Mycorrhizal fungal networks weigh about five times the mass of the entire human population on Earth. That's enormous. Hidden beneath the soil, these systems span an estimated 110 quadrillion kilometers globally, and to put that distance in perspective, if these ultra-thin underground threads were unraveled and connected into a single continuous line, they would stretch nearly a billion times the distance between the Earth and the sun. So these massive fungal webs form close symbiotic relationships with plant roots, acting as a key highway system for nutrients and carbon storage. It's a hidden world.

For decades, scientists have recognized that these systems exist beneath our feet. They're linked to roughly 80 percent of all plant species on Earth. And wherever plants grow, these fungi are almost always present. But their global distribution, total mass, and exact density have remained unmapped until now, when a new modeling effort has finally revealed their true scale and identified the regions where they're most heavily concentrated, as well as the areas where they're rapidly disappearing.

How scientists mapped the underground webs

Quantifying a hidden global network wasn't easy. It demanded a massive data gathering effort. Researchers began by analyzing previous scientific literature, collecting data from 16,000 geolocated soil core samples taken from diverse ecosystems around the globe. These samples let the team measure the actual length of fungal threads within specific volumes of soil. Using this dataset, the team applied machine learning models to generate predictive maps of fungal networks across the entire planet, highlighting areas of high density and pointing out regions where more physical sampling is still needed.

But there's a catch. Knowing the length of the threads is only part of the equation. To determine the actual weight of the network, researchers had to find a way to measure the width of these microscopic structures. So working alongside AMOLF, a research institute in Amsterdam, the team utilized a specialized robot equipped with a camera to track and record the growth of fungal networks over time in a laboratory setting. This video data provided the precise measurements needed to calculate the total biomass of the living networks.

The structural design of microscopic pipes

They're incredibly thin , less than a single strand of human hair. But these networks are built from threads called hyphae, and despite their microscopic size, they function as active, living pipes that transport vital materials back and forth between plants and the fungal network. They can navigate tight soil spaces. Plant roots simply can't penetrate those spaces, so it's their thinness that makes all the difference.

A two-way underground economy

Plants and fungi trade. It's a mutual exchange built on giving and taking,plants provide the fungi with carbon, and in return the fungi deliver critical nutrients gathered from deep underground. Let's break this down.

• Fungi extract phosphorus and nitrogen from deep soil layers and deliver them directly to plant roots.
• In exchange, plants transfer carbon to the fungal networks, which sequester approximately 1 billion tons of carbon underground every year.
• This massive carbon drawndown prevents that carbon from entering the atmosphere and contributing to global warming.

Massive biomass concentrated in unprotected grasslands

The numbers tell a different story. But it's not dense tropical forests that hold most of this underground mass,it's wild grasslands. According to the study, wild grassland ecosystems contain about 40 percent of the global biomass of arbuscular mycorrhizal fungi, and these open habitats host some of the most concentrated fungal webs on the planet.

There's a major problem here. Grasslands are among the least protected ecosystems on Earth, and they're being cleared and converted into agricultural fields at four times the rate of forests, which devastates the underground networks.

"The plants are growing better, and carbon's being drawn down. That all depends on having dense fungal networks and soils that are active and alive," said Justin Stewart, an evolutionary ecologist and lead author of the study.

The vast scale of unmapped underground territory

But researchers stress we're only seeing a fraction of the full picture, even with this new map. The current study focused exclusively on living arbuscular mycorrhizal networks. Dead fungal networks were not included. They continue to store carbon and influence soil ecosystems long after the fungi have died, so the total organic footprint of these systems is likely much larger than the current estimate of five times human mass.

But huge gaps in our knowledge remain. Scientists don't fully understand the precise drivers behind fungal loss or the long-term ecological consequences of their decline, and previous work indicates that 90 percent of fungal communities worldwide currently lack any form of formal environmental protection. So many geographic regions, like the deserts of the American Southwest, remain almost entirely unstudied.

We still lack practical solutions for soil restoration. Corentin Bisot, an AMOLF biophysicist and co-author of the study, explained that scientists are far from understanding how to actively increase microbes and fungi in a local grassland. They simply don't have the toolbox to do it yet.

Presenting the findings to global policymakers

Toby Kiers, the executive director and co-founder of the organization that led the research, noted that this study represents a major shift in our understanding of soil ecology. But this is just the start. Kiers stated that this is the moment where researchers went from simply knowing that this system exists to actually understanding where it is, how dense it is, and where it has been lost. It's a starting point. The map serves as a starting point, much like early, imperfect historical maps, which will be refined as more soil data is collected.

Researchers are taking action. To address the ongoing loss of these networks, they plan to bring their findings directly to international climate discussions by attending the upcoming United Nations Climate Change Conference, COP31, and presenting their data to global policymakers. It's a critical moment. Their goal is to highlight the role these subterranean networks play in carbon storage and to advocate for policies that protect the living soils necessary to keep these carbon-sequestering systems alive. But they can't do it alone.