According to research published in Science by the Society for the Protection of Underground Networks (SPUN), scientists have mapped roughly 110 quadrillion kilometres of arbuscular mycorrhizal fungal hyphae in the top 15 centimetres of global soil. This vast living infrastructure, which covers about 70 percent of land plant species, forms a critical underground circulatory system that moves carbon, water, and nutrients across ecosystems.
Measuring the Global Fungal Network Beneath Our Feet
To calculate the staggering scale of these networks, researchers combined more than 16,000 soil core measurements with robotic imaging of over 300,000 living fungal structures grown in the laboratory, according to study details released by SPUN. Led by Dr. Justin Stewart alongside co-lead author Dr. Corentin Bisot of the AMOLF physics institute, the team fed environmental variables like temperature, rainfall, and soil chemistry into machine-learning models to predict hyphal density where direct sampling was impossible.
The resulting figure of 110 quadrillion kilometres—equivalent to 110 followed by fifteen zeros—is a modeled estimate rather than a direct census. According to arithmetic breakdowns of the data, laid end to end, that thread would reach the Sun roughly 733 million times over and stretch more than a tenth of the way across the Milky Way galaxy. The living network contains around 300 megatonnes of carbon, which is four to six times the total mass of every human alive, as reported by SPUN researchers.
Did You Know? In just a single teaspoon of healthy soil, there can be up to 10 metres of living fungal thread. Scoop up a handful from a meadow, and you are holding biological infrastructure comparable to the height of a three-story building.
Agricultural Pressures and Biodiversity Hotspots
The global density map identifies major hotspots in Florida’s Everglades, the Sudd flooded grasslands of South Sudan, and the Tibetan Plateau. However, according to a 2025 SPUN analysis cited in the research, approximately 95 percent of these AM fungal biodiversity hotspots sit entirely outside protected areas, leaving them vulnerable to land-use changes.
Grasslands globally are being converted to cropland at roughly four times the rate of forest loss. According to study co-author Katie Field, a professor of plant-soil processes at the University of Sheffield, croplands hold about half the fungal density of the wild ecosystems they replace. Tilling physically breaks hyphae apart, while synthetic fertilizers and fungicides disrupt the natural trade where plants exchange fixed carbon for phosphorus and nitrogen supplied by the fungi.
Frequently Asked Questions
What are arbuscular mycorrhizal fungi?
Arbuscular mycorrhizal (AM) fungi are microscopic networks of tubular cells called hyphae that thread through soil and plant roots, trading water and mineral nutrients for carbon, according to SPUN research.
How much fungal network exists in the soil?
According to a study published in Science, researchers estimate there are roughly 110 quadrillion kilometres of AM fungal hyphae in the top 15 centimetres of global soil.
Do agricultural practices harm these underground networks?
Yes. According to researchers like University of Sheffield professor Katie Field, tilling breaks fungal threads apart, while synthetic fertilizers reduce a plant’s need to trade carbon with fungi, leading to lower overall network density in croplands.
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