In a single teaspoon of soil, up to 10 meters of delicate fungal threads may twist and stretch—living filaments so vast that, if laid end-to-end, they would span nearly a billion times the distance from Earth to the sun. These are the hidden highways of arbuscular mycorrhizal (AM) fungi, an underground network now mapped in unprecedented detail by scientists with the Society for the Protection of Underground Networks (SPUN). For the first time, researchers have produced global maps revealing not just where these fungal networks thrive, but how much biomass they represent and how much carbon they quietly pull from the atmosphere. The findings, published in Science, underscore a quiet miracle beneath our feet—one that could be pivotal in the fight against climate change.
Nearly all land plants partner with AM fungi, exchanging carbon for water and nutrients in a symbiosis that has shaped terrestrial life for over 400 million years. These fungal networks act as a living circulatory system, channeling carbon deep into soils. The study reveals they sequester an estimated 4 billion tons of CO2 annually—equivalent to 11% of global human emissions. This invisible infrastructure, long overlooked in climate models and conservation plans, is now being brought into focus through data from over 16,000 soil cores collected across nine biomes and analyzed from 322 published studies. Using machine-learning models refined with robotic imaging of more than 300,000 living hyphae at Amsterdam’s AMOLF institute, the team created the Mycorrhizal Infrastructure Map, an interactive tool offering estimates for every square kilometer of land on Earth.
The maps reveal that grasslands are the powerhouse of fungal biomass, harboring 40% of the planet’s AM fungal networks. Hotspots include South Sudan’s vast flooded grasslands, the Everglades in Florida, and the high-altitude plains of the Tibetan Plateau. In contrast, croplands show only about half the fungal density of wild ecosystems—a deficit that could weaken soil resilience and reduce carbon storage. Alarmingly, previous research indicates that 90% of AM fungal biodiversity hotspots lie outside protected areas, and the new data suggest their physical infrastructure is just as exposed.
"Fungi have been ignored in climate and conservation for too long," says SPUN executive director and study co-author Toby Kiers. "Now is the time to change that trajectory." With a growing understanding of their role, these underground networks could become central to land management, regenerative agriculture, and global conservation strategies. As the Mycorrhizal Infrastructure Map becomes a tool for policymakers and land stewards, it offers not just data, but direction—toward a future where what lies beneath is no longer invisible.