A new study published in the journal Science has mapped the global distribution of arbuscular mycorrhizal fungal networks. Researchers compiled data from 16,669 soil cores collected across 322 previous studies to analyze these networks.

The study used machine learning to create predictive maps of fungal network density for every square kilometer of topsoil worldwide. "This is the moment where we went from knowing that this system exists to really knowing where it is, how dense it is and where it's been," said Toby Kiers, executive director and co-founder of the Society for the Protection of Underground Networks.

The networks extend approximately 110 quadrillion kilometers globally. If connected in a single line, these fungal threads would nearly reach a billion times the distance between Earth and the sun. These fungi form symbiotic relationships with around 80 percent of the world's plant species, providing plants with nutrients like phosphorus and nitrogen in exchange for carbon.

The networks sequester an estimated 1 billion tons of carbon underground each year. This translates to absorbing approximately 4.3 billion tons of carbon dioxide equivalent annually, which represents about 11 percent of global fossil fuel emissions in 2021. The total mass of these living fungal networks is estimated to be five times the combined mass of all humans on Earth.

"The study helps us come to grips with how important these below ground organisms can be to everything that we see above ground," said James Bever, professor of ecology and evolutionary biology at the University of Kansas. The plant-fungus interfaces consist of hyphae, which are thinner than a human hair and transport nutrients and carbon.

Wild grassland ecosystems contain about 40 percent of the world's fungal biomass. In croplands, fungal network densities are approximately 50 percent lower compared to wild ecosystems. "A global map of arbuscular mycorrhizal fungal network density and biomass was urgently needed and can inform more efficient strategies for biodiversity conservation and restoration, agricultural management, and climate change mitigation," said Andrea Genre, expert in arbuscular mycorrhizal fungi at the University of Turin. Researchers plan to present the findings to policymakers at a United Nations climate conference.