Subterranean fungi networks more than 100 quadrillion km in length, study finds
First ever global mapping of arbuscular mycorrhizal fungi shows scale of hyphal systems that sustain plant life
Arbuscular mycorrhizal fungi are networks of tubular cells called hyphae. Photograph: Alf Jacob Nilsen/Alamy
Our planet's soils contain enough of the subterranean fungi that sustain plant life and help regulate the climate to stretch from the Earth to the sun almost three-quarters of a billion times, a groundbreaking new study has found.
Arbuscular mycorrhizal fungi are networks of tubular cells called hyphae that sustain life on Earth by forming critical partnerships with more than 70% of plants. The networks, which have been forming for about 475 million years, provide nutrients and water in exchange for the carbon produced by the plants, and help to regulate the climate by drawing carbon into soils.
And yet, despite their importance, very little is known about their distribution and density across natural ecosystems. This was one of the reasons that the Society for the Protection of Underground Networks (Spun) was set up in 2021 by a global network of scientists and researchers.
Now, in a new study published in Science andreferred to as "one of the most exciting of my career" by one researcher, a Spun team have used machine-learning models with data from more than 16,000 soil cores from around the world to produce the first ever global map of arbuscular mycorrhizal fungi networks.
They calculated that the fungi networks, if stretched end to end, would reach a length of 110 quadrillion kilometres, which is almost 750m times the distance from the Earth to the sun.
"There could be up to 10 metres (32ft) of mycorrhizal network in just a teaspoon of soil," said Dr Justin Stewart, lead author of the study.
The densest networks of arbuscular mycorrhizal fungi are found in grasslands
Density of arbuscular mycorrhizal fungi, measured in metres of hyphae (branching filaments) per cubic centimetre of soil
- Sudd wetlands, South Sudan: 8.05 metres per cm3
- Tibetan Plateau, China: 11.40 metres per cm3
- Flint Hills prairie, US: 10.29 metres per cm3
Guardian graphic. Source: Spun Note: examples are all montane and flooded grasslands in the top 1% globally.
The study also documents potential threats to this life-giving infrastructure, with the researchers finding that, on average, network densities in cropland are 47.3% lower than in wild ecosystems.
"A lot of large-scale agriculture practices harm fungal networks," said Stewart. "The most apparent way is with something like tilling, where you go into a soil and literally rip it up." Fertilisers or fungicides can also "disrupt the symbiosis between the plants and the fungi".
The scientists warned that the consequences of the loss of fungal networks could be wide ranging. Lower-density fungal networks reduce the soil's ability to store carbon and distribute nutrients, and the networks also protect waterways from nitrogen, phosphorus and other chemicals.
"If they disappear, there's going to be a lot more chemicals going into waterways," said Dr Toby Kiers, an author of the study, who called the study one of the most exciting of her life. "Ultimately, the aim of the research is to help scientists and decision-makers understand where fungal systems are thriving and where they are threatened. We will be presenting these data to governments at the upcoming desertification Cop in Mongolia in August."
Through their mapping, the researchers found that grasslands contained the densest hyphal systems. Regions including the Everglades in Florida, the Sudd flooded grasslands of South Sudan, and prairie and steppe ecosystems globally were all found to have "exceptionally high" density.
However, the study highlights that these regions are often poorly protected and are becoming increasingly degraded.
The researchers also called for closer collaboration between farmers and fungi. Stewart noted that current crop yields were artificially boosted by heavy fertiliser use. He argued that if farmers were encouraged to protect and support soil fungi, plants could obtain more nutrients naturally, reducing the need for fertilisers, while the fungi would help transfer more carbon deep into the soil, improving carbon storage.
Kiers said: "There's a big movement now to not only restore communities above ground, the things that you can see, the plants and animals, but also to restore underground fungal communities. And this dataset allows us to have benchmarks for what a healthy microbial community can look like."
The biologist and co-author Dr Merlin Sheldrake said the study helped to find "ways that we can better work with fungi to help address many of the unfolding challenges of our times, from food security to climate change".
