Scientists have mapped the global density and biomass of fungal mycelium networks, revealing a vast underground infrastructure that supports plants, soil health, and carbon flow. The findings show why protecting living soils and reducing intensive agricultural disruption could be crucial for biodiversity, climate resilience, and future food systems.
Beneath our feet lies a living infrastructure we cannot see,but one on which much of plant life, soil health, and even the climate depend. These are not roots, tunnels, or a single network like a cable crossing the planet. They are microscopic fungal filaments that spread through the soil and form vital associations with plants. We are talking about mycelium.
Now, for the first time, an international team of researchers has managed to estimate, on a global scale, the density and biomass of these networks.
The study, titled Global density and biomass of arbuscular mycorrhizal fungal networks and published in Science, gathered data from 322 studies, with more than 16,000 soil samples distributed across nine biomes. The team then applied machine-learning models to estimate where these networks are concentrated and to build a global map of one of Earth’s most important and least visible biological infrastructures. They also calibrated the biomass model using robotic images of more than 300,000 living hyphae—the filaments that make up fungal structure—grown in the laboratory.
The result might be hard to grasp: researchers estimate that the planet’s topsoils contain around 110 quadrillion kilometers of living hyphae—110,000,000,000,000,000 kilometers. If placed end to end, they would stretch for a distance equivalent to hundreds of millions of times the distance between Earth and the Sun, according to calculations reported by The Guardian.
The figure is staggering, and the discovery shows that these fungi play a much larger role than they usually get credit for in conversations about biodiversity, agriculture, and climate change.
What Is Mycelium, and Why Does Life Need It?
Arbuscular mycorrhizal fungi live in association with the roots of approximately 70% of plant species. This relationship is an ancient alliance: plants provide the fungi with carbon produced through photosynthesis, and the fungi help plants obtain nutrients and water from the soil.
In simple terms, fungal mycelium works like an extension of plant roots. Its hyphae are so fine that they can explore spaces in the soil that roots cannot reach. In doing so, they help plants absorb key nutrients such as phosphorus and nitrogen, which are essential for growth and for resisting adverse conditions.
This relationship also matters for agriculture. Crops such as wheat, corn, and rice can benefit from these associations because fungi expand the roots’ ability to capture resources. In healthy soils, this cooperation can improve nutrient-use efficiency and help plants better tolerate stresses such as drought.
That is why some scientists describe mycelium as a kind of underground circulatory system, because it moves essential resources through ecosystems.
Everything Is Connected: Mycelium, a Fungal Network Crucial to Carbon, Soil, and Climate
The study estimated that these networks have a biomass of around 300 megatonnes, several times greater than the combined biomass of all living humans. This mycelium also participates in the movement of enormous amounts of carbon into the soil.
According to the research, these fungal networks transport around 1 billion metric tons of carbon into soils each year. Some institutions express this as close to 4 billion tons of carbon dioxide equivalent, a figure close to 11% of annual CO₂ emissions generated by human activity.
This does not mean fungi can “solve” climate change. But it does show that living soils are a central part of the global carbon cycle. When these networks function properly, they help store carbon, sustain soil structure, and maintain more resilient ecosystems.
Researchers found that flooded savannas, wetlands, and grasslands harbor an especially important share of this fungal infrastructure: around 40% of the global total. Its “capitals,” then, are not major cities but landscapes such as the Sudd in South Sudan, the Florida Everglades, the Tibetan Plateau, and India’s Banni grasslands. Beneath their less disturbed soils, these networks appear to reach some of their highest densities.
However, many of these ecosystems remain poorly protected and are rapidly being converted for agricultural use.
The Threat of Intensive Agriculture
The other side of the discovery comes as a warning. In intensively farmed land, mycorrhizal networks appear far less dense than in natural ecosystems. The study and reports about it point to reductions of nearly 50% in large-scale crop areas.
Possible causes include intensive tillage, the overuse of fertilizers and pesticides, and soil degradation. When plants receive nutrients artificially and soil is constantly disturbed, its relationship with mycelium can weaken. And when that relationship breaks down, the soil loses part of its capacity to recycle nutrients, store carbon, and withstand droughts or other environmental shocks.
That is why the authors argue that these maps go beyond simple scientific curiosity. They can help decide which ecosystems to protect, where to restore degraded soils, and how to design agricultural practices that are more compatible with underground life. The idea is for these maps to reveal where fungal networks are thriving, where they are under pressure, and which territories should be prioritized for conservation or restoration.
The main lesson behind the study is a simple, but powerful one: soil is not an inert support structure where plants grow. It is a living, connected, and fragile world. And much of the planet’s health depends on what happens down there, silently, long before anything breaks through the surface.
Cover image created with AI
