Scientists Map the World's Underground Fungi

A team of scientists working through the Society for the Protection of Underground Networks, better known by its acronym SPUN, has published the first global map of soil mycorrhizal fungi in the journal Science. The research shows that the underground network these fungi build runs to a total length of about 110 trillion kilometers, a scale that had not been quantified in this way before.

Mycorrhizal fungi are not a new subject in biology. It has been known for decades that they live in the soil and that their thin threads, called hyphae, connect to plant roots. What was missing was a map showing where these networks are densest and how much of them exists across the planet. The new study fills exactly that gap, drawing on data gathered from several continents.

How do you measure something buried underground?

The map was built by combining three approaches. The first is soil samples taken from a large number of locations, which give a direct view of where fungi are present and how dense they are. The second is machine learning, which estimates conditions in places that were not sampled based on the measured values. The third is laboratory testing, used to check and calibrate the results. By layering these three elements, the researchers produced an estimate of distribution at a global scale.

The figures that emerge from the map are large. The total mass of the network is estimated at around 300 megatonnes of carbon, several times the combined mass of every person alive today. According to the data, the densest layers of fungi are found in high mountain grasslands and in grasslands that flood periodically. These are habitats where the symbiosis between plants and fungi plays a particularly important role in keeping vegetation alive.

It is worth stressing that these are estimates rather than exact counts. The network is underground, vast and shifting, so every figure carries a degree of uncertainty. Machine learning helps fill the gaps, but it also introduces assumptions that future samples may correct. The authors present the map as a first step, a baseline that later research will refine and amend.

Why does this network matter at all?

Mycorrhizal fungi form a symbiosis with about 70 percent of plant species on Earth. The exchange runs both ways. The fungi deliver nutrients and water from the soil to plants, and in return they receive carbon that plants produce through photosynthesis. That exchange links individual plants into a wider underground structure and shapes the health of whole ecosystems.

This is where the practical value of the map lies. Knowing where the networks are densest and most sensitive makes it easier to judge which areas deserve protection. SPUN exists to draw attention to the underground part of nature, which is often overlooked in conversations about biodiversity precisely because it is invisible. The map gives those conversations a concrete tool.

It helps to be precise about what the study shows and what it does not. It offers a global estimate of the network’s spread and mass, but it does not prove how these networks will behave under pressure from climate change or intensive agriculture. Those remain questions for future work. In your view, what role should invisible networks like these play in plans to protect nature?