Global map reveals the vast scale of underground fungal networks

Plants and fungi are interacting beneath our feet Andrea Obzerova/Alamy Just under Earth’s surface, 110 quadrillion kilometres of carbon-rich fungi intersect with plant roots. This vast network has been laid bare in the first global digital map of our planet’s mycelial networks. Not only do these fungi exchange nutrients with plants, they also help regulate our climate. First, the researchers analysed data from 16,000 soil samples from across Earth, derived from 322 previous studies. They also used robotic imaging to measure more than 300,000 fungal threads grown in the lab, allowing them to estimate the total biomass and carbon stored in the networks. Next, the team combined that data and used it to extend estimates across deserts, tundra, forests and other regions where direct measurements were sparse or unavailable. The results suggest that worldwide arbuscular mycorrhizal fungi networks harbour a mass of carbon equivalent to about five times that of all living humans combined. “They’re very important for a lot of the different functions of our planet,” says Stewart. “For example, they pull carbon underground – that’s important for climate change.” The researchers also estimate that around 40 per cent of the world’s arbuscular mycorrhizal fungi live in grassland ecosystems, especially those of South Sudan, the Florida Everglades and the Tibetan plateau. That’s concerning, they say, since grasslands are rapidly being transformed into farmlands. Croplands, meanwhile, show significantly reduced fungal presence, with large-scale crop-growing soils associated with about 50 per cent lower network densities than those in uncultivated ecosystems, despite their high presence of plants. That could be because fungicides can kill fungi directly, while tilling can break apart their networks and heavy fertiliser use may undermine the nutrient-for-carbon trade that normally sustains the symbiosis, says Stewart. Last year, Laura Carter at the University of Leeds, UK, and her colleagues revealed that azole antifungals – a widely employed class of chemicals used to control fungal diseases like mildew and rot in crops – cut the density of hyphae (the long, straw-like tube cells of fungi) by around 70 per cent and reduced the extent to which beneficial fungi colonise plant roots 80 per cent. Kiers says they plan to present the findings to policy-makers at the United Nations desertification summit in Mongolia this August. Science DOI: 10.1126/science. adu4373 Topics: fungi Receive a weekly dose of discovery in your inbox. We'll also keep you up to date with New Scientist events and special offers.