Science Publishes First Global Map of Arbuscular Mycorrhizal Fungal Networks

The journal Science published on Thursday the first global map of arbuscular mycorrhizal fungal filament density. The map shows 110 quadrillion kilometres of carbon-rich fungal threads intersecting plant roots just beneath Earth’s surface. Researchers compiled data from 16,000 soil samples drawn from 322 earlier studies.

They also used robotic imaging to measure more than 300,000 fungal threads grown in laboratory conditions. The team combined these measurements to estimate total biomass and carbon storage, then extended the estimates to regions with limited direct sampling. Worldwide, the networks contain a mass of carbon equivalent to about five times that of all living humans combined.

Around 40 per cent of the fungi occur in grassland ecosystems. High-density areas were identified in South Sudan, the Florida Everglades and the Tibetan plateau. Large-scale crop-growing soils showed roughly 50 per cent lower network densities than uncultivated ecosystems.

Azole antifungals reduced hyphal density by about 70 per cent and cut beneficial fungal colonisation of roots by up to 80 per cent, according to separate measurements by Laura Carter at the University of Leeds and colleagues. Justin Stewart of the Society for the Protection of Underground Networks said the findings quantify losses that may affect nutrient access, drought resilience and carbon storage in agricultural soils.

Steven Allison at the University of California, Irvine, noted that farmers could add fungal spores or reduce tillage and fertiliser use to rebuild biomass.

The team also released an interactive map displaying the global distribution of the networks. Toby Kiers, also at the Society for the Protection of Underground Networks, said the group plans to present the results to policy-makers at the United Nations desertification summit in Mongolia this August.