Researchers have mapped an estimated 110 quadrillion kilometres of arbuscular mycorrhizal fungal hyphae in Earth’s topsoils. Published in Science by the Society for the Protection of Underground Networks, the global density map reveals a vast subterranean network supporting roughly 70 per cent of plant species worldwide.
Measuring Earth’s 110 Quadrillion Kilometre Subterranean Network
Earth’s topsoils contain an estimated 110 quadrillion kilometres of thread-like structures called arbuscular mycorrhizal fungal hyphae, also known as AM fungi. Fungus is a type of eukaryotic organism including yeasts, molds, and mushrooms, which are distinguished from the plant kingdom because fungal cells lack chloroplasts or the organelles that conduct photosynthesis. Often referred to as AM fungi, these tubular cells weave through soil and into plant roots, forming part of the ancient infrastructure connecting ecosystems beneath our feet, having formed symbiotic relationships with plant life over the past 475 million years. A teaspoon of healthy soil can hold up to 10 metres of living fungal thread, according to findings published in the journal Science.
To grasp the scale of the 110 quadrillion kilometre estimate, laying the threads end to end would reach the Sun nearly a billion times over, or span just under 10 per cent of the entire width of the Milky Way galaxy. In contrast, when measured as more than 621 trillion miles, connecting every AM fungal network end to end in one big line would be long enough to span the distance from Pluto to the sun—which is 3.6 billion miles away—roughly 172,500 times. The measurement relies on data drawn from more than 16,000 soil cores collected globally, combined with machine-learning models trained on environmental variables such as temperature, rainfall, and soil chemistry where direct sampling was not possible.
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,
The research team was led by Dr. Justin Stewart from the Society for the Protection of Underground Networks, alongside co-lead author Dr. Corentin Bisot of the AMOLF physics institute in Amsterdam. To complement the field data, the team used robotic imaging to analyze more than 300,000 living fungal structures grown in laboratory conditions, producing an interactive visualization built with data designer Moritz Stefaner.
How Fungal Networks Circulate Nutrients and Carbon
Often described as Earth’s underground circulatory system, AM fungi form mutually beneficial relationships with roughly 70 per cent of the world’s plant species. Plants provide the fungi with carbon produced through photosynthesis, while the fungal networks help plants absorb water and essential mineral nutrients from the soil. Because mycorrhizal fungi are thinner than most plant roots, they come into contact with more soil per volume, helping them absorb nutrients and redirect them back to the host plant while sending additional water to surrounding plant life.
These underground networks can expand the effective foraging area of plant roots by up to 100 times and provide more than 80 per cent of a partnered plant’s phosphorus needs. Across grassland, forest, tundra, and cropland ecosystems, the fungi move roughly 4 billion tonnes of carbon dioxide equivalent into soils every year, accounting for about 11 per cent of annual human-related carbon dioxide emissions. The global infrastructure contains roughly 300 megatons of carbon, which equals four to six times the mass of all living humans.
Agricultural Pressures on Global Grassland Hotspots
The mapping project identified specific regional hotspots where fungal density peaks, including Florida’s Everglades, the Sudd flooded grasslands of South Sudan, and the Tibetan Plateau. Grasslands alone account for roughly 40 per cent of Earth’s AM fungal infrastructure. However, researchers noted that these critical zones face mounting pressure from land conversion.
Grasslands are being converted to agricultural land at roughly four times the rate at which forests are lost. Tilling physically breaks hyphae apart, while synthetic fertilisers and fungicides disrupt the natural exchange between plant roots and fungi.
Furthermore, previous SPUN analysis indicated that 95 per cent of AM fungal biodiversity hotspots sit outside protected areas, raising concerns about the long-term stability of these underground networks.
Future Research and International Policy Next Steps
The newly released global density maps are designed to help researchers and policymakers identify both thriving underground networks and vulnerable areas requiring enhanced protection.
As scientists continue to explore the capabilities of subterranean fungi—including unrelated research into fungal intelligence and pattern recognition, such as a 2024 study on wood-eating Phanerochaete velutina fungus exhibiting very intelligent
behavior according to researcher Yu Fukasawa, PhD—experts emphasize that safeguarding these hidden networks remains essential to preventing ecosystem collapse and addressing climate change.