Scientists Measure Earth’s Vast Underground Fungal Webs

A hidden circulatory system pulses just beneath the planet’s surface. There, embedded in the soil, are dense networks of microorganisms known as arbuscular mycorrhizal fungi. These fungi attach themselves to the roots of plants, sending long, thin filaments out through the soil. These ferry water and nutrients to plants and whisk away carbon, helping to keep vast quantities of it out of the atmosphere.

Laid end to end, these filaments would extend for 68 quadrillion miles — roughly 730 million times the distance between Earth and the sun, scientists reported in a new paper. Collectively, the filaments contain approximately 300 megatons of carbon, or four to six times as much as the carbon contained by all the human beings on the planet, according to the study, which was published in Science on Thursday.

An international team of scientists conducted the research, using a combination of advanced techniques, including machine learning and a high-resolution imaging robot, to measure, predict and map the size of these fungal networks in ecosystems across the globe.

The study revealed particularly dense fungal networks beneath the world’s grasslands, adding to the evidence that these ecosystems, which tend to receive less conservation protection than forests, serve as significant carbon sinks for the planet.

“People just aren’t paying attention to these ecosystems,” said Toby Kiers, director of the Society for the Protection of Underground Networks, or SPUN, and an evolutionary biologist at Vrije University Amsterdam; she was also an author of the new paper. “What we want to do with these data is really shine a light on some of these hidden patterns underground.”

More than 70 percent of Earth’s terrestrial plant species rely on arbuscular mycorrhizal fungi, which — in addition to transporting nutrients and storing carbon — also help stabilize the soil and protect plants from environmental stress.