Beneath the surface of our planet lies an intricate and colossal network of life that has remained largely invisible to human eyes until now. Vast, interconnected systems of fungi are quietly underpinning terrestrial ecosystems, playing a fundamental role in supporting plant life and, critically, in regulating the Earth’s climate by facilitating the movement of carbon into soils. In a groundbreaking achievement, an international team of researchers has unveiled the first comprehensive global maps, detailing the distribution and sheer magnitude of these subterranean fungal networks worldwide.
The pioneering study, recently published in the prestigious journal Science, zeroes in on arbuscular mycorrhizal (AM) fungi. These microscopic powerhouses form symbiotic relationships with an estimated 70% of all plant species on Earth, creating a biological partnership that is essential for the health and vitality of nearly every terrestrial biome. Complementing the release of these critical maps, scientists have also launched an interactive digital visualization, allowing individuals from all walks of life to explore the remarkable scale and complexity of this hidden underground infrastructure. These unprecedented maps are poised to become an invaluable tool for scientists, conservationists, and policymakers, enabling them to pinpoint areas where these vital fungal networks are flourishing and, conversely, where they may be under significant threat.
The Unseen Architects of Ecosystems: Arbuscular Mycorrhizal Fungi
Arbuscular mycorrhizal fungi, often referred to simply as AM fungi, are not merely passive inhabitants of the soil; they are active participants in a mutually beneficial exchange that sustains much of the plant kingdom. In this intricate partnership, plants, through the process of photosynthesis, provide AM fungi with essential carbon compounds. In return, the fungi act as an extended root system for the plants, vastly increasing their capacity to absorb vital nutrients, such as phosphorus and nitrogen, and access scarce water resources from the soil. This symbiotic relationship is so profound that many plants would struggle to survive, let alone thrive, without their fungal partners.
These underground networks function as a living, dynamic infrastructure, not only sustaining individual plants but also underpinning the stability and resilience of entire ecosystems. Their role in sequestering carbon, effectively drawing it down from the atmosphere and storing it within the soil, is a critical component of the planet’s natural carbon cycle and a vital mechanism for climate regulation. Building upon previous foundational research, including a significant global analysis of underground mycorrhizal fungal diversity published in Nature in 2025 and the development of the "Underground Atlas" digital platform, this latest study marks a pivotal moment. For the first time, scientists have embarked on a systematic effort to quantify and map the physical density and global distribution of the AM fungal networks themselves, moving beyond simply cataloging their diversity.
Quantifying a Planetary Network: 110 Quadrillion Kilometers of Fungal Threads
The creation of these new global maps represents a monumental undertaking, involving the meticulous compilation of data from over 16,000 soil cores collected from diverse locations across the globe. To bridge the gaps in direct sampling, researchers employed sophisticated machine-learning models. These models integrated extensive environmental data, encompassing information from arid deserts, frigid tundra, lush forests, and a myriad of other ecosystems, to predict the density of fungal networks in regions where direct measurements were not feasible.
Further enhancing the accuracy and detail of the study, the research team collaborated with the Physics of Behavior group at the AMOLF research institute. Utilizing cutting-edge robotic imaging techniques, they analyzed more than 300,000 living AM fungal hyphae cultivated under controlled laboratory conditions. This multi-faceted approach, combining field sampling, advanced computational modeling, and precise laboratory analysis, allowed researchers to achieve a groundbreaking estimation of both the total length and the sheer mass of the global AM fungal network.
The findings are staggering: their analysis suggests that these intricate AM fungal networks stretch for an astonishing approximately 110 quadrillion kilometers worldwide. To put this into perspective, this distance is equivalent to traversing the Earth to the Sun and back over 580 million times. Furthermore, the total carbon contained within these networks is estimated to be around 300 megatons. This figure is a remarkable 4 to 6 times the estimated total mass of all living humans on Earth, underscoring the profound biological significance and sheer volume of this hidden world.
"It is hard to overstate the importance and enormity of these fungi," stated lead author Dr. Justin Stewart, affiliated with the Society for the Protection of Underground Networks (SPUN). "There could be up to 10 meters (32 feet) of mycorrhizal network in just a teaspoon of soil." This vivid analogy highlights the incredible density and ubiquitous presence of these fungal structures even in seemingly unremarkable soil samples.
Earth’s Subterranean Circulatory System: A Vital Artery for Life
Scientists frequently liken mycorrhizal networks to one of Earth’s vital circulatory systems. Just as blood vessels transport oxygen and nutrients throughout the human body, these fungal networks serve as conduits for the movement of carbon, essential nutrients, and water throughout underground ecosystems. This constant flow is fundamental to maintaining soil health, nutrient cycling, and the overall functioning of terrestrial environments.
In healthy, undisturbed soils, these fungal networks can dramatically expand the reach of plant roots, effectively increasing their foraging area by up to an astounding 100 times. This enhanced nutrient uptake is particularly crucial for phosphorus, with AM fungi often supplying more than 80 percent of a plant’s requirement for this essential element. This symbiotic efficiency allows plants to thrive in diverse conditions and contributes to robust plant growth, which in turn supports herbivores and the entire food web.
"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," commented co-lead author, Dr. Corentin Bisot, a biophysicist at AMOLF. "We are learning how the complex bodies of network-forming fungi transport nutrients and help regulate the climate." This sentiment reflects a broader scientific awakening to the critical, yet often overlooked, roles played by fungi in planetary processes.
A New Visual Frontier: The Mycorrhizal Infrastructure Map
To translate these complex scientific findings into an accessible and engaging format, the researchers collaborated with award-winning data visualization designer Moritz Stefaner. Together, they developed the "Mycorrhizal Infrastructure Map," an interactive online tool designed to vividly showcase the study’s results. This innovative map provides the most detailed global overview to date of Earth’s fungal infrastructure. Estimates of fungal network density were calculated for every square kilometer of terrestrial landmass, with exclusions made for permanent ice caps and regions where data was insufficient to generate reliable predictions.
The underlying data powering these maps has been made publicly available. This crucial step empowers governments, conservation organizations, and other decision-makers with novel and robust tools for monitoring the health and extent of underground fungal communities, a vital step towards informed conservation strategies.
This groundbreaking work builds upon a significant body of previous research published by several of the same authors in Nature. Those earlier studies delved into the intricate mechanisms by which mycorrhizal fungi and plants collaborate to create highly efficient systems for exchanging carbon and nutrients. Through precise measurements, researchers observed carbon movement through these living networks at speeds reaching 120 micrometers per second. If a human were able to navigate within these fungal pathways, these speeds would translate to an astonishing 400 kilometers per hour, highlighting the dynamic nature of these subterranean flows. The current study extends this research by examining how these critical flows operate at a planetary scale, revealing their global ecological significance.
Identifying Areas of Concern: Threats to Subterranean Ecosystems
While the maps illuminate the widespread presence of these vital fungal networks, they also highlight significant areas of concern and identify regions where these ecosystems are under particular pressure. A striking observation is that network densities in agricultural croplands are predicted to be approximately half of those found in comparable wild ecosystems. This reduction in fungal network health in cultivated lands suggests a potential compromise in soil fertility and carbon sequestration capacity in areas critical for food production.
Furthermore, the analysis reveals that wild grasslands harbor a substantial portion of the world’s arbuscular mycorrhizal biomass, estimated at roughly 40%. Despite their critical ecological role and the immense fungal diversity they support, grasslands remain among the least protected ecosystems on Earth. Alarmingly, they are being converted to agricultural land at a rate four times faster than forests, indicating a significant and accelerating threat to these fungal communities and the ecosystems they sustain.
These findings corroborate previous research conducted by SPUN, which indicated that a staggering 95% of biodiversity hotspots for arbuscular mycorrhizal fungi lie outside of established protected areas. This disparity underscores a critical gap in current conservation efforts, suggesting that a significant portion of Earth’s fungal biodiversity is vulnerable and inadequately safeguarded.
For Dr. Toby Kiers, Executive Director of SPUN and a renowned evolutionary biologist, the accumulating evidence from this and other studies points to an urgent need to integrate fungi into global climate and conservation planning. Dr. Kiers, a recent recipient of a MacArthur Fellowship and the Tyler Prize, often referred to as the "Nobel Prize for the Environment," for her pioneering work on plant-fungal relationships, emphasizes the urgency. "Fungi have been ignored in climate and conservation for too long. Now is the time to change that trajectory," she asserts, advocating for a paradigm shift in how we perceive and protect these essential organisms.
Unanswered Questions and the Path Forward
Despite the revolutionary insights provided by these new maps, the researchers acknowledge that significant knowledge gaps remain regarding the intricate distribution and function of mycorrhizal fungi. "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 towards 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."
The new maps, while revealing the extraordinary scale of Earth’s underground fungal networks, also serve as a roadmap for future scientific inquiry. Large regions of the world remain undersampled, presenting a clear directive for upcoming research efforts. Understanding the intricate dynamics of these vital, yet largely invisible, ecosystems is paramount for developing effective strategies to address pressing global challenges, including climate change mitigation, sustainable agriculture, and biodiversity conservation. The ongoing exploration of this hidden world promises to unlock further secrets about the planet’s intricate life support systems and guide us toward a more harmonious coexistence with the natural world.
