Scientists have unveiled the first global map of arbuscular mycorrhizal fungi, revealing an underground network so extensive that it stretches an estimated 110 quadrillion kilometers across Earth's topsoil.
A Hidden System Beneath Our Feet
These fungi live as thin filaments called hyphae, weaving through soil and connecting with plant roots. In this partnership, plants share carbon-rich sugars, while fungi deliver phosphorus, nitrogen, and water back to the roots. Researchers say this symbiosis has existed for about 450 million years and supports roughly 70% of plant species.
The study combined data from 322 research papers, more than 16,000 soil cores, climate and soil information, and machine-learning models to estimate fungal density across vegetated land. Robotic imaging also helped measure hyphae at scale, offering a rare look at a system that usually remains invisible underground.
Grasslands Emerge as Major Hubs
One of the most striking findings is where these fungi are most concentrated. Instead of forests, wild grasslands appear to host some of the densest networks on the planet. The study estimates that about 40% of these fungi are found in grasslands, including regions such as the Tibetan Plateau, the Flint Hills Prairie, the Everglades, and the Sudd Wetlands.
By contrast, large-scale croplands showed fungal network densities that were about 47% to 50% lower than those in wild ecosystems. The researchers note that plowing, heavy fertilizer use, and fungicides may all contribute to weakening these underground systems.
Why It Matters
Beyond supporting plant growth, these fungal webs help shape soil structure and move carbon into the ground, where some of it can remain stored. The team estimates that arbuscular mycorrhizal fungi channel around 1 billion metric tons of carbon into soils each year.
The map is still a first draft, with some regions under-sampled, but it offers a powerful new view of life below the surface. As soil science advances, this hidden network could become central to how we think about ecosystems, farming, and climate resilience in the future.