First Global Mapping of Arbuscular Mycorrhizal Fungi Reveals Vast Underground Networks
New research has revealed that the subterranean fungi essential for sustaining plant life and regulating the climate extend across Earth’s soils in networks so vast they could stretch from the planet to the sun nearly 750 million times. This groundbreaking study provides the first global mapping of arbuscular mycorrhizal fungi, highlighting the immense scale of their hyphal systems.
Arbuscular mycorrhizal fungi consist of tubular cells known as hyphae that have been forming symbiotic relationships with over 70% of plant species for approximately 475 million years. These networks facilitate the exchange of nutrients and water for carbon produced by plants, playing a critical role in climate regulation by sequestering carbon in soils.
Despite their ecological importance, there has been limited understanding of their global distribution and density across natural ecosystems. This knowledge gap motivated the establishment of the Society for the Protection of Underground Networks (Spun) in 2021, a coalition of international scientists and researchers dedicated to studying these fungal systems.
In a study published in Science, described by one researcher as “one of the most exciting of my career,” the Spun team employed machine-learning models analyzing data from over 16,000 soil cores worldwide to generate the first comprehensive global map of arbuscular mycorrhizal fungi networks.
The researchers estimated that if the fungi’s hyphal networks were extended end to end, their length would total 110 quadrillion kilometres—approximately 750 million times the distance from 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 study also identifies significant threats to these vital networks, noting that fungal network densities in cropland are on average 47.3% lower than those in wild ecosystems.
“A lot of large-scale agriculture practices harm fungal networks,”
Stewart explained.
“The most apparent way is with something like tilling, where you go into a soil and literally rip it up.” He added that fertilisers and fungicides can also disrupt the symbiotic relationship between plants and fungi.
The scientists cautioned that the degradation of fungal networks could have extensive consequences. Reduced network density diminishes soil’s capacity to store carbon and distribute nutrients effectively. Additionally, these networks help protect waterways by filtering nitrogen, phosphorus, and other chemicals.
“If they disappear, there’s going to be a lot more chemicals going into waterways,”
said Dr Toby Kiers, co-author of the study, who described the research as 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 UN Convention to Combat Desertification in Mongolia in August.”
Mapping Reveals Densest Networks in Grasslands
The mapping revealed that grasslands host the densest hyphal systems. Regions such as the Everglades in Florida, the Sudd flooded grasslands of South Sudan, and various prairie and steppe ecosystems worldwide exhibited exceptionally high fungal network densities.
However, the study highlights that these ecosystems are often inadequately protected and face increasing degradation.
The researchers advocate for enhanced collaboration between farmers and fungal communities. Stewart pointed out that current crop yields are artificially elevated through heavy fertiliser application. He suggested that encouraging farmers to conserve and support soil fungi could enable plants to access nutrients more naturally, reducing fertiliser dependence. Furthermore, the fungi would facilitate deeper carbon transfer into soils, enhancing carbon storage.
“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.”
said Kiers.
Biologist and co-author Dr Merlin Sheldrake emphasized the study’s potential to inform solutions for global challenges.
“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.”
