A study published Saturday in the journal Science has produced the first global map of Earth's underground fungal networks, estimating that the microscopic filaments linking plant roots to their fungal partners stretch a combined 110 quadrillion kilometers through the top 15 centimeters of soil — a distance so vast it exceeds the span between Earth and the nearest star system, Alpha Centauri, by a factor of roughly three. The analysis, led by researchers at the University of Colorado and collaborating institutions across five continents, used machine learning to synthesize data drawn from more than 16,000 soil samples compiled across 300 previous studies conducted over four decades of ecological fieldwork.
The networks are composed of structures called hyphae, the thread-like filaments that fungi extend through soil in search of nutrients and water. Hyphae from arbuscular mycorrhizal fungi — a class that forms symbiotic partnerships with approximately 72 percent of all plant species on Earth — are individually far thinner than a human hair but collectively form a living infrastructure that researchers have long suspected plays a critical role in sustaining ecosystems worldwide. What the new study demonstrates for the first time is both the physical scale of that infrastructure and its highly uneven distribution across climate zones, biomes, and land use types.
Carbon, Climate, and Agriculture
Beyond its sheer geographic scale, the fungal web performs a function of enormous consequence for the global carbon cycle. The study found that arbuscular mycorrhizal networks draw approximately 4 billion tons of carbon dioxide from the atmosphere into soils each year — a quantity comparable to the combined annual CO2 emissions of the United States and the European Union. That carbon, once incorporated into fungal biomass and stabilized organic matter deep in the soil profile, can remain sequestered for decades, making these networks one of the planet's most effective natural mechanisms for removing greenhouse gases from the atmosphere.
The research also found that agricultural soils, which cover roughly 40 percent of Earth's ice-free land surface, host significantly lower densities of hyphal networks than undisturbed grasslands, temperate forests, and wetlands. Conventional farming practices — particularly mechanical tilling, which physically severs fungal threads — and the intensive application of synthetic nitrogen fertilizers, which reduce plants' biological incentive to maintain fungal partnerships, have sharply diminished the carbon-capturing capacity of cropland soils. "What we are mapping is a planetary-scale biological infrastructure that we have been systematically degrading for more than a century without fully understanding what we were losing," said a lead author of the study at a press briefing in Vienna Saturday.
What the Map Reveals About Soil Health
The map, which assigns hyphal density estimates to every square kilometer of topsoil on Earth's land surface, is expected to serve as a reference tool for environmental scientists, agricultural researchers, climate modelers, and policymakers for years to come. Among its most striking findings: the highest hyphal densities on the planet are found in old-growth temperate rainforests, including in the Pacific Northwest, and in undisturbed tropical forests, while the lowest densities appear in heavily irrigated croplands and degraded urban soils. Oregon and the broader Pacific Northwest emerged in the analysis as among the most biologically dense fungal regions anywhere on Earth, consistent with the region's reputation as a global hotspot for mycological diversity and forest ecological complexity.
The study's authors noted that the research carries direct implications for climate policy and carbon accounting. If farming practices that restore hyphal networks — including no-till cultivation, cover cropping, and reduced synthetic fertilizer application — can be demonstrated to measurably increase soil carbon sequestration in verifiable ways, they could qualify as legitimate offset methodologies under voluntary carbon markets and, potentially, under Article 6 of the Paris Agreement, which governs international carbon trading among signatory nations. That prospect has already attracted the attention of several large agribusiness companies and carbon market developers who have begun examining the study's data for commercial applications.
Ecologists at Oregon State University, who were not part of the research team but provided peer review commentary to the journal, called the findings "a landmark contribution that fundamentally reframes how we should think about soil — not as an inert agricultural substrate, but as a living, climate-regulating system whose biological integrity we have been eroding at scale." They cautioned that translating the map's estimates into actionable policy would require extensive field-level verification, as the machine learning predictions carry uncertainty intervals that widen considerably in regions where historical soil sampling data is sparse, including parts of sub-Saharan Africa, Central Asia, and the high Arctic.