Scientists Publish First Global Map of Underground Mycorrhizal Fungi

An international research team has produced the first global map of the vast underground network of arbuscular mycorrhizal (AM) fungi, the threadlike organisms that live in soil and connect to plant roots. These fungi have quietly supported plant life on Earth for millions of years, but their true scale and spread had never been measured at a worldwide level until now. The findings were published in the journal Science.

To build the map, the scientists used machine learning together with data from more than 16,000 soil samples taken around the world. They found that the world's topsoils hold roughly 110 quadrillion kilometres of fungal threads, called hyphae. That length is so large it equals almost a billion round trips between the Earth and the Sun. The networks also store around 300 million tonnes of carbon, several times the combined weight of all humans alive today.

These fungi survive by forming a give-and-take partnership with plants. They share nutrients with roots and in return receive carbon from the plant. Through this exchange, AM networks are estimated to lock away about 4 billion tonnes of carbon dioxide equivalent every year, which is close to 11 percent of all carbon emissions caused by human activity. This makes them a quietly powerful part of the natural climate system.

The study also pointed to where these networks are richest and where they are in danger. Grassland regions, including South Sudan, the Tibetan plateau and the Banni grasslands in India, together hold about 40 percent of the world's AM fungal networks. But the researchers warned that farmland usually has around half the fungal density of wild land, and grasslands are being turned into farms about four times faster than forests are being cleared. This places these underground systems at serious risk.

By putting a number on this "living infrastructure" beneath our feet, the researchers hope to move fungi from the edges of environmental policy to the centre of climate action. Protecting healthy soils, they argue, is not only about farming but also about keeping a major natural carbon store intact.