Beneath the Earth’s surface, extensive networks of fungi quietly sustain plant life and play a critical role in regulating the planet’s climate by facilitating carbon storage in soils. Researchers have now created the first global maps documenting the distribution and extent of these underground fungal networks, offering unprecedented insights into their global footprint.
The study, published in Science, focuses on arbuscular mycorrhizal (AM) fungi—organisms that form partnerships with approximately 70% of plant species worldwide. Alongside the research, scientists unveiled an interactive visualization enabling exploration of the remarkable scale of this hidden underground infrastructure. The maps will aid researchers and policymakers in identifying regions where these fungal networks thrive and where they face threats.
Key findings include:
- Global topsoils contain an estimated 110 quadrillion kilometers (68 quadrillion miles) of AM fungal networks, composed of thread-like hyphae. This distance exceeds the Earth-Sun separation by nearly a billionfold.
- Grasslands account for roughly 40% of Earth’s AM fungal infrastructure, with particularly dense networks predicted in South Sudan’s flooded grasslands, Florida’s Everglades, and the Tibetan Plateau.
- AM fungal networks sequester an estimated 4 billion tons of CO2 equivalent annually—equivalent to 11% of human-caused carbon emissions.
- Agricultural croplands exhibit approximately 50% lower network densities compared to wild ecosystems, potentially reducing soil carbon storage, nutrient cycling, and resilience to environmental stress.
The Hidden Partnerships Supporting Plant Life
Arbuscular mycorrhizal fungi exchange carbon from plant photosynthesis for nutrients and water, forming mutually beneficial relationships with most plant species. These underground networks function as living infrastructure, sustaining ecosystems and transporting carbon into the soil. Prior work in Nature (2025) highlighted mycorrhizal efficiency in carbon-nutrient exchange, while the new study expands this understanding to a planetary scale.
Mapping 110 Quadrillion Kilometers of Fungal Networks
Researchers compiled data from over 16,000 soil cores and used machine learning models integrating environmental data from deserts, tundra, and forests to predict fungal density in unsampled regions. Collaborating with AMOLF’s Physics of Behavior group, they analyzed 300,000 hyphae using robotic imaging. This synthesis revealed the global network spans roughly 110 quadrillion kilometers and contains 300 megatons of carbon—four to six times the biomass of all humans.
“The magnitude of these fungi is staggering—there could be up to 10 meters of mycorrhizal network in a single teaspoon of soil,” said Dr. Justin Stewart of SPUN.
Earth’s Underground Circulatory System
Mycorrhizal networks act as Earth’s circulatory system, distributing carbon, nutrients, and water. In healthy soils, they enhance plant foraging by 100-fold and supply over 80% of a plant’s phosphorus needs.
“Advanced imaging, robotics, and machine learning are revealing subterranean secrets,” said co-lead author Dr. Corentin Bisot. “We’re uncovering how fungal networks regulate climate and transport nutrients.”
A New Global Fungal Infrastructure Map
Designed by data visualization expert Moritz Stefaner, the Mycorrhizal Infrastructure Map provides the most detailed view of Earth’s fungal networks. Estimates cover every 1km² of land, excluding ice caps and data-deficient regions. The public dataset equips governments with tools to monitor fungal ecosystem health.
The study builds on previous SPUN research showing mycorrhizal carbon transport at speeds up to 120 um/sec (~400km/hr). While the maps illuminate this infrastructure’s scale, large regions remain unsampled, guiding future research into one of Earth’s most vital yet understudied ecosystems.
Threats to Underground Fungal Ecosystems
Croplands have half the network density of wild areas, and grasslands—which hold 40% of AM fungi—are being converted four times faster than forests. SPUN research indicates 95% of mycorrhizal biodiversity hotspots lie outside protected zones.
“Fungi have been overlooked in climate and conservation efforts for too long,” said Dr. Toby Kiers, SPUN Executive Director and recent MacArthur Fellow. “Now is the time to change that.”
Future Research Directions
“Despite their ancient role in shaping life, we know too little about their planetary distribution,” said Dr. Merlin Sheldrake. “These maps offer a roadmap to address food security and climate challenges by partnering with fungi.”
The study underscores the urgent need to protect grasslands and integrate fungal ecosystems into conservation strategies, as their loss accelerates soil degradation and climate instability.
