First Global Map Estimates 110 Quadrillion Kilometres of Underground Fungal Networks

Researchers have produced the first global digital map of Earth’s underground fungal networks, revealing 110 quadrillion kilometres of carbon-rich threads that intersect with plant roots just beneath the surface. Justin Stewart, Toby Kiers and colleagues at the Society for the Protection of Underground Networks compiled data from 16,000 soil samples drawn from 322 earlier studies.

They supplemented those records with robotic imaging of more than 300,000 fungal threads grown in laboratory conditions, then extended the measurements to deserts, tundra and other regions with limited direct sampling.

The resulting estimates indicate that worldwide arbuscular mycorrhizal fungi networks contain a mass of carbon equivalent to about five times that of all living humans combined. These fungi form symbiotic relationships with roughly 70 per cent of the world’s plant species, supplying nutrients and water in exchange for carbon from the plants.

The map shows that about 40 per cent of the global arbuscular mycorrhizal fungi population resides in grassland ecosystems, including those in South Sudan, the Florida Everglades and the Tibetan plateau.

Large-scale crop-growing soils, by contrast, support roughly 50 per cent lower network densities than uncultivated land. Laura Carter and colleagues at the University of Leeds, UK, previously found that azole antifungals reduce fungal hyphal density by around 70 per cent and cut beneficial colonisation of plant roots by as much as 80 per cent.

Steven Allison at the University of California, Irvine, noted that the reduced biomass under croplands may limit nutrient access, drought resilience and carbon storage for agricultural plants.