Modern agriculture is weakening the fungi that keep soils fertile
Beneath every prairie, wetland, and backyard lies a living infrastructure older than forests themselves — a web of fungal filaments stretching, in aggregate, nearly a billion times the distance from Earth to the Sun. For the first time, scientists have mapped these underground networks globally, revealing that grasslands, long overlooked in favor of forests, are the true strongholds of arbuscular mycorrhizal fungi, organisms that have quietly sustained plant life and carbon cycles for 450 million years. The map arrives as a warning as much as a discovery: intensive agriculture has already halved fungal density in croplands, and what humanity does next with this knowledge may determine the long-term fertility of its soils.
- A global scientific effort has produced the first-ever map of Earth's underground fungal networks, quantifying 110 quadrillion kilometers of living filaments in the world's topsoils — a scale that strains human comprehension.
- The findings upend a long-held assumption: grasslands, not forests, are the planet's fungal hotspots, harboring 40% of arbuscular mycorrhizal fungi and storing vast amounts of carbon safely below ground where fire and drought cannot easily reach it.
- Each year these fungi move an estimated 3.12 billion tonnes of carbon dioxide equivalent from plant photosynthesis into the soil, yet they remain almost entirely absent from global biodiversity assessments and climate policy frameworks.
- Intensive farming — through tillage, heavy fertilizers, and fungicides — has reduced fungal density by nearly half in managed croplands, quietly dismantling the biological infrastructure that keeps soils fertile without chemical dependency.
- Scientists now have a baseline from which to work, and the next challenge is translating this map into conservation and agricultural policy before further losses make restoration exponentially harder.
Walk across a prairie or wetland and you are standing atop one of Earth's most expansive living systems — invisible, ancient, and only now being understood at a planetary scale. A new international study has mapped, for the first time, the underground networks of arbuscular mycorrhizal fungi, finding approximately 110 quadrillion kilometers of fungal filaments threaded through the world's topsoils. Stretched end to end, they would span the distance from Earth to the Sun nearly a billion times over. These organisms have been sustaining plant life for more than 450 million years, likely enabling plants to colonize land in the first place.
The relationship between these fungi and plants is one of nature's most fundamental exchanges. Fungal filaments extend into soil that plant roots cannot reach, delivering water and nutrients; in return, plants share carbon captured through photosynthesis. It is a transaction that happens entirely out of sight, yet it underpins the health of most terrestrial ecosystems on Earth.
One of the study's most striking findings is that grasslands — prairies, steppes, savannas, and wetlands — are the true hotspots of fungal abundance, harboring around 40 percent of the world's arbuscular mycorrhizal fungi. Places like the Sudd wetlands of South Sudan, the Florida Everglades, and the Tibetan Plateau rank among the densest. Because grasslands store much of their carbon below ground through these fungal networks, they are far more resilient to wildfire and drought than previously appreciated — a finding that challenges the conventional focus on forests in climate and conservation discussions.
The carbon implications are substantial. Each year, these fungi channel an estimated 3.12 billion tonnes of carbon dioxide equivalent into the soil, and they collectively contain around 300 megatonnes of carbon. Yet they remain largely invisible in global climate and biodiversity assessments.
The urgency sharpens when agriculture enters the picture. Intensively managed croplands contain nearly half the fungal density of comparable natural ecosystems. Tillage, heavy fertilizer use, and fungicides disrupt and suppress these networks, leaving soils increasingly dependent on external chemical inputs. Healthy fungal communities, by contrast, improve nutrient cycling, strengthen soil structure, and help plants withstand stress — functions that no synthetic input fully replicates.
This global map is a beginning, not a conclusion. Scientists now have a baseline for where these networks exist and how extensive they are. The work ahead — understanding how to protect and restore them — will shape whether agriculture can become genuinely sustainable and whether soils can remain fertile as the climate continues to shift. The answers, quite literally, lie beneath our feet.
Walk across a prairie, a wetland, or even your own backyard, and you're standing atop one of Earth's most vast and vital living systems—one you cannot see. Beneath the soil lies a network of fungal filaments so extensive that if you could stretch them all out, they would reach from here to the sun and back nearly a billion times over. A new global study has mapped these underground fungal highways for the first time, revealing that the world's topsoils contain approximately 110 quadrillion kilometers of living fungal threads. The scale is almost incomprehensible, yet these organisms have been quietly sustaining plant life and entire ecosystems for more than 450 million years.
These fungi, known as arbuscular mycorrhizal fungi, form partnerships with the roots of most land plants on Earth. The relationship is ancient and mutually beneficial: the fungi extend their thread-like filaments, called hyphae, into soil that plant roots cannot reach, helping plants acquire water and essential nutrients. In return, plants provide the fungi with carbon they've captured through photosynthesis. This exchange is so fundamental that it likely enabled plants to colonize land in the first place. Today, it remains one of nature's most important transactions, yet it happens entirely out of sight.
The research, an international effort drawing on data from hundreds of sites across continents, reveals that grasslands—not forests—are the true hotspots for underground fungal abundance. Prairies, steppes, savannas, and wetlands collectively harbor around 40 percent of the world's arbuscular mycorrhizal fungi. Some of the densest concentrations exist in places like the Sudd wetlands of South Sudan, the Florida Everglades, and the Tibetan Plateau. This finding challenges the conventional focus on trees and forests when discussing carbon storage and ecosystem conservation. Grasslands, supported by their extensive fungal networks, store much of their carbon below ground, making them far more resilient to wildfires, droughts, and storms than previously understood.
The carbon implications are staggering. Each year, these fungi channel an estimated 3.12 billion tonnes of carbon dioxide equivalent from plant photosynthesis into the soil. Collectively, they contain around 300 megatonnes of carbon. Yet despite this enormous contribution to how the planet cycles carbon and maintains ecosystem health, fungal networks remain largely invisible in global assessments of biodiversity and climate resilience. Scientists are only now beginning to account for what has always been there.
The stakes become even clearer when you look at agriculture. Intensively managed croplands contain nearly half the fungal density found in comparable natural ecosystems. Practices like intensive tillage, heavy fertilizer application, and fungicide use disrupt or suppress these fungal networks. Coupled with evidence that the same practices reduce fungal diversity, a troubling pattern emerges: modern industrial farming is simplifying and weakening the very fungal communities that keep soils fertile and crops productive. When fungal networks decline, soils become dependent on external chemical inputs. Healthy, diverse fungal networks, by contrast, improve nutrient cycling, enhance soil structure, boost plant productivity, and help plants withstand environmental stress.
The implications for future food security are significant. As agriculture faces pressure to become more sustainable and resilient in the face of climate change, protecting and restoring these underground networks could prove essential. The fungi are not a luxury or an afterthought—they are infrastructure. Yet they remain largely absent from conversations about farming's future.
It's worth noting that popular culture has sometimes overstated what these fungal networks do. Claims that they function as a "wood wide web" where trees exchange nutrients and send warning signals to one another have captured public imagination, but scientists caution that such claims exceed the current evidence. While fungal networks undoubtedly connect plants and facilitate resource exchange, researchers are still working to understand exactly how these relationships operate under real-world conditions.
This global map represents a crucial first step. For the first time, scientists have a baseline understanding of where these fungal networks exist and how much of them covers the planet. The next phase of research will focus on how to protect and restore them. That work will determine whether agriculture can become truly sustainable, whether soils can remain fertile without endless chemical inputs, and whether ecosystems can maintain their resilience as the climate shifts. The answer lies beneath our feet, in a world we are only now learning to see.
Notable Quotes
Modern agricultural intensification is simplifying and diminishing the fungal communities that help keep soils fertile, crops productive and ecosystems resilient.— Research team
To improve soil health, strengthen food security and build resilience to climate change, we need to pay more attention to the life-support system beneath our feet.— Research team
The Hearth Conversation Another angle on the story
When you say 110 quadrillion kilometers of fungal filaments, what does that actually look like in soil? Can you picture it?
Not really—it's too vast. But think of it this way: if you took a handful of healthy soil, it would be threaded through with these invisible filaments, like the soil itself is woven. They're so fine you'd need a microscope to see them, but they're everywhere, connecting to plant roots, exploring spaces the roots can't reach.
And the plants are feeding these fungi carbon in exchange for water and nutrients. That's a trade. But why has agriculture disrupted it so badly?
Because we've treated soil as inert—just a medium to hold plants up while we dump fertilizer on top. Intensive tillage tears apart the fungal networks. Fungicides kill them. Heavy fertilizer means plants don't need the fungi as much, so the relationship weakens. We've essentially told the soil it doesn't need to work anymore.
So by using more chemicals, we've made soil more dependent on chemicals.
Exactly. It's a trap. The fungi that would naturally cycle nutrients and build soil structure are gone, so we need more inputs. And the more inputs we use, the harder it is for the fungi to come back.
The study found that grasslands, not forests, are the real carbon storage hotspots. That's surprising.
It is, because we've been so focused on saving forests. But grasslands store their carbon below ground, in the soil and in these fungal networks. That makes it much safer—fire can't burn it, drought can't dry it out. It's protected by the very system we've been ignoring.
What happens next? Is anyone actually trying to restore these networks on farms?
That's the frontier now. Some farmers are experimenting with reduced tillage, cutting back on fungicides, using cover crops. But it's slow. The science is clear about what we've lost. Now we have to figure out how to get it back.