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| An image taken in Bhutan from the research expedition. Photo Credit: Courtesy of University of Sheffield |
Scientific Frontline: Extended "At a Glance" Summary: Global Arbuscular Mycorrhizal Fungal Networks
The Core Concept: Arbuscular mycorrhizal (AM) fungal networks are vast underground systems that form symbiotic relationships with the majority of Earth's plant species, exchanging water and nutrients for plant-fixed carbon. A recent global mapping effort revealed these living infrastructures possess a total length of approximately 110 quadrillion kilometers and a mass of roughly 300 megatons of carbon.
Key Distinction/Mechanism: Unlike standard root systems, AM fungi act as ecosystem engineers that penetrate plant roots and extend extensively into the soil, functioning as a planetary circulatory system. This hyper-efficient network increases root foraging areas by up to 100 times, transporting water, nutrients, and an estimated four billion tons of carbon dioxide equivalent into soils annually.
Origin/History: While mycorrhizal fungi have shaped terrestrial life for hundreds of millions of years, the first global distribution map and mass quantification of AM networks was published in 2026 by an international team including the University of Sheffield, AMOLF, and the Society for the Protection of Underground Networks (SPUN).
Major Frameworks/Components:
- Symbiotic Exchange: The mutually beneficial transfer of plant-generated carbon for fungi-sourced phosphorus (providing up to 80 percent of a plant's needs) and water.
- Predictive Modeling: The use of machine learning algorithms calibrated with robotic imaging of living fungal hyphae and density data from over 16,000 global soil cores.
- Ecosystem Distribution: The identification of wild grasslands as critical biodiversity hubs holding roughly 40 percent of the world's AM biomass, contrasting with agricultural croplands which exhibit an approximate 50 percent reduction in network density.
Branch of Science: Mycology, Soil Ecology, Biogeochemistry, and Evolutionary Biology.
Future Application: High-resolution mapping tools and digital visualization (such as the Mycorrhizal Infrastructure Map) will enable governments and decision-makers to monitor underground ecosystem health, optimize agricultural practices, and integrate soil fungi into precision climate and conservation policies.
Why It Matters: These largely invisible networks are foundational to plant productivity, global nutrient cycling, and ecosystem resilience. By drawing massive amounts of carbon into the soil, they play a crucial role in mitigating climate change, making their protection—especially in vulnerable, unprotected grassland habitats—vital for environmental stability and future food security.
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| Screenshot of interactive map. Image Credit: Society for the Protection of Underground Networks |
For the first time, an international team of researchers has mapped the global distribution and mass of arbuscular mycorrhizal (AM) fungal networks. These vast underground systems sustain plant life and play a critical role in regulating Earth’s climate by locking carbon into the soil.
Published alongside an interactive visualization that helps reveal the scale of this underground fungal infrastructure, the research will help scientists and decision-makers understand where these vital fungal systems are thriving and where they are threatened.
AM fungi form symbiotic relationships with approximately 70 percent of plant species on Earth. The fungi provide nutrients and water in exchange for carbon fixed by plants. As ecosystem engineers, these networks form a critical living infrastructure that draws carbon into soils and supports much of life on Earth. Last year, in Nature, researchers published global analyses of the diversity patterns of underground mycorrhizal fungal communities accompanied by a digital tool, the Underground Atlas, to help decision-makers locate predicted underground biodiversity hotspots. But until now, no one has attempted to predict and visualize the physical density and global distribution of AM fungal networks.
Study contributor Katie Field, a professor of plant-soil processes at the University of Sheffield and a Royal Society Faraday Discovery Fellow, said, “These findings are exciting and significant because they provide the first global view of AM fungal networks, revealing an extensive but largely invisible living infrastructure that underpins plant productivity, nutrient cycling, ecosystem resilience, and the health of terrestrial ecosystems worldwide.
“This study not only represents a major advance in quantifying these hidden fungal networks and identifying key hotspots such as grasslands, but it also highlights important knowledge gaps surrounding the ecological functioning of these networks.”
The researchers assembled data on the density of AM networks from over 16,000 soil cores collected across Earth. They developed machine learning models that incorporated data layers from deserts and tundra to forests to predict network density in unsampled ecosystems. In collaboration with the Physics of Behavior group at the research institute AMOLF, the team calibrated their model with robotic imaging of over 300,000 living AM fungal hyphae grown in the lab.
Using these datasets, they estimate that AM fungal networks have a total length of approximately 110 quadrillion kilometers and a mass of around 300 megatons of carbon (four to six times the mass of all living humans).
“It is hard to overstate the importance and enormity of these fungi,” said lead author Dr. Justin Stewart, with the Society for the Protection of Underground Networks (SPUN).
“There could be up to 10 meters of mycorrhizal network in just a teaspoon of soil.”
Often called one of Earth’s circulatory systems, mycorrhizal networks move carbon, water, and nutrients across underground ecosystems. In healthy soils, mycorrhizal networks can increase the foraging area of plant roots by up to 100 times, while providing more than 80 percent of a plant’s phosphorus.
“With the emergence of new technologies in high-resolution imaging, machine learning, and robotics, we are starting to reveal what has long been hidden under our feet,” said co-lead author Dr. Corentin Bisot, an AMOLF biophysicist.
“We are learning how the complex bodies of network-forming fungi transport nutrients and help regulate the climate.”
The team worked with award-winning data visualization designer Moritz Stefaner to build the Mycorrhizal Infrastructure Map. It is the first time Earth’s fungal infrastructure has been seen at this scale and resolution. The underlying data are available to download for governments and decision-makers to begin monitoring the health of critical underground fungal communities.
Last year, several of the same authors published a cover story in Nature in which they described how mycorrhizal fungal networks and their plant partners build hyper-efficient supply chains for the exchange of carbon and nutrients, measuring carbon flows inside these living transport systems that can reach speeds of up to 120 micrometers per second. The current study is a critical step toward understanding how carbon and nutrient flows unfold on a global scale.
The study also documented potential threats. Mycorrhizal densities across croplands are predicted to be roughly half those in wild ecosystems. Wild grassland ecosystems were found to contain approximately 40 percent of the world’s AM biomass. Yet grasslands are among Earth’s least protected ecosystems and are being transformed into farmlands four times faster than forests. This reinforces a finding published by SPUN researchers last year showing that 95 percent of the biodiversity hotspots for AM fungi are located outside protected areas.
For evolutionary biologist Dr. Toby Kiers, executive director of SPUN, this growing body of research is critical in developing more precise climate policies: “Fungi have been ignored in climate and conservation for too long. Now is the time to change that trajectory.” Kiers was recently named a prestigious MacArthur Fellow and winner of the Tyler Prize, known as the "Nobel Prize for the Environment," for her work on plant-fungal systems.
“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,” added co-author and biologist Dr. Merlin Sheldrake.
“This study is an exciting step toward understanding how this planetary circulatory system operates and suggests ways that we can better work with fungi to help address many of the unfolding challenges of our times, from food security to climate change.”
This study helps quantify the extraordinary extent of AM fungal networks, but it also reveals how much remains unknown by pinpointing many regions of the planet that remain unsampled.
Professor Katie Field added: “Importantly, the research shows that large-scale agricultural croplands exhibit an approximately 50 percent reduction in AM fungal network density compared with less intensively managed systems. On the face of it, this seems alarming.
“However, as stated by the authors, our understanding of how specific environmental conditions and agricultural practices influence mycorrhizal health, carbon storage, and nutrient cycling remains very limited. In other words, although we are now starting to understand where these networks occur, we still know relatively little about what they do, how effectively they function, and how their roles vary across environments and host plants.”
Addressing this gap is one of the central aims of Professor Field's new Royal Society Faraday Discovery Fellowship based at the University of Sheffield in collaboration with Lancaster University and the Natural History Museum. Building on recent advances, Professor Field’s project will investigate the ecological performance and functional capacity of mycorrhizal networks across diverse environmental and management contexts.
Research material: A Hidden Infrastructure
(Interactive map by SPUN: Society for the Protection of Underground Networks)
Published in journal: Science
Title: Global density and biomass of arbuscular mycorrhizal fungal networks
Authors: Justin D. Stewart, Corentin Bisot, Rachael I. M. Cargill, Michael E. Van Nuland, Heidi-Jayne Hawkins, Loreto Oyarte Galvez, Malin Klein, Marije Van Son, Victoria Terry, Louis Paré, Claudia Banchini, Franck Stefani, Felix Kahane, Kai-Kai Lin, Renato K. Braghiere, Katie J. Field, Nadejda A. Soudzilovskaia, Jinsu Elhance, Vasilis Kokkoris, Merlin Sheldrake, James T. Weedon, Thomas S. Shimizu, Stuart West, and E. Toby Kiers
Source/Credit: University of Sheffield
Edited by: Scientific Frontline
Reference Number: bio061426_02