Global map shows fungal networks bury vast carbon

A first global digital map of arbuscular mycorrhizal fungi networks estimates 110 quadrillion kilometres of carbon-rich fungal threads under Earth’s surface. Researchers quantify how much carbon these underground partnerships store, and they warn that cropland

Just under Earth’s surface. a carbon-rich web stretches farther than most people can picture: 110 quadrillion kilometres of fungal threads intersect with plant roots. A team has now turned that hidden infrastructure into the first global digital map of mycelial networks. revealing the scale of a partnership that feeds plants while also pulling carbon underground—an effect researchers say matters for climate as well as for soil health.

Arbuscular mycorrhizal fungi. an ancient group of soil fungi found throughout most terrestrial ecosystems. form symbiotic relationships with about 70 per cent of the world’s plant species. In exchange for carbon from plants, the fungi provide nutrients and water. Justin Stewart. at the Society for the Protection of Underground Networks. puts it bluntly: “Some people call plants the saviours of these fungi. but these fungi are also the saviours of plants.” He adds. “If you’re not in symbiosis with arbuscular mycorrhizal fungi. you’re kind of the weirdo of the plant world.”.

Stewart and colleagues set out to quantify what has largely remained out of sight. They asked. “can we map the Earth’s underground circulatory system?” says Toby Kiers. also at the Society for the Protection of Underground Networks. The approach combined existing measurements with lab and modelling work. First, the researchers analysed data from 16,000 soil samples from across Earth, derived from 322 previous studies. They then used robotic imaging to measure more than 300. 000 fungal threads grown in the lab. enabling estimates of the total biomass and carbon stored in the networks. Finally. they combined those results to extend estimates across deserts. tundra. forests and other regions where direct measurements were sparse or unavailable.

The picture that emerges is staggering: the worldwide networks harbour a mass of carbon equivalent to about five times that of all living humans combined. Stewart says these fungi are “very important for a lot of the different functions of our planet. ” including that they “pull carbon underground – that’s important for climate change.”.

The map also shows where the underground infrastructure appears strongest. The researchers 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. They call that concerning because grasslands are being rapidly transformed into farmlands.

In croplands, the story changes. Large-scale crop-growing soils show significantly reduced fungal presence. with network densities associated with about 50 per cent lower than those in uncultivated ecosystems—despite high plant presence. Stewart suggests multiple pressures may be at work: fungicides can kill fungi directly. tilling can break apart their networks. and heavy fertiliser use may undermine the nutrient-for-carbon trade that sustains the symbiosis.

That concern isn’t coming out of nowhere. Last year. Laura Carter at the University of Leeds in the UK and her colleagues revealed that azole antifungals—widely employed chemicals used to control fungal diseases like mildew and rot in crops—cut the density of hyphae by around 70 per cent and reduced the extent to which beneficial fungi colonise plant roots by up to 80 per cent. Carter. linking her earlier findings with the new map. says: “Supporting arbuscular mycorrhizal fungi isn’t just an ecological issue; it is a practical route to improving soil health. resilience and long-term crop productivity.” She adds that “suggests current practices may be undermining a key natural ally of crops.”.

Steven Allison of the University of California. Irvine. is especially focused on what thinner networks under croplands could mean for farming. “With that biomass being knocked down so much. our agricultural crops may be missing out on some key benefits like nutrient access. drought resilience and carbon storage. ” he says.

Still. the researchers argue the new work has a silver lining: once losses are quantified. it becomes easier to design ways to rebuild fungal biomass. Allison says. “Farmers could add fungal spores to their soils. ” and that the study might also prompt adjustments to field practices—reducing tillage or adding less fertiliser.

Even with the scale revealed, the map is careful about what it does and doesn’t claim. Stewart says the findings don’t mean all fungi are connected in a global “wood wide web. ” a hypothesised underground network through which plants exchange resources and information. “Our research here was just asking how many threads are there on Earth. not if this is one large. continuous network.”.

Alongside the study, the team has launched an interactive map showing the global distribution of fungal networks in unprecedented detail. Kiers says the researchers plan to present the findings to policy-makers at the United Nations desertification summit in Mongolia this August.

mycelial networks arbuscular mycorrhizal fungi soil health carbon storage fungal spores croplands grasslands fungicides azole antifungals tillage nutrient cycling climate change desertification summit