Long invisible, fungi weave global networks whose total length reaches hundreds of quadrillions of kilometers. An international team has produced the first worldwide map, radically changing our view of soils.
Arbuscular mycorrhizal fungi live in symbiosis with more than 70% of land plants. For 475 million years, they have provided water and minerals to plants in exchange for carbon produced by photosynthesis. Until now, no one had attempted to estimate their density on a planetary scale.
World map of the density of arbuscular mycorrhizal fungal hyphae.
Credit: Truth & Beauty / Moritz Stefaner. Justin Stewart - SPUN Numbers that defy comprehension
By gathering more than 16,000 soil samples and using machine learning, researchers calculated that the total length of these filaments reaches 110 quadrillion kilometers (approx. 68.4 quadrillion miles). "110 what?" some may ask: that is 110,000 billion, but to better grasp this distance, know that it corresponds to... nearly a billion round trips between Earth and the Sun! The extent of the density and distribution of fungal networks is also shown in an interactive visualization on
this site.
The mass of these fungi represents about 300 megatonnes of carbon (approx. 330 million short tons), or 4 to 6 times the weight of all living humans. In a single teaspoon of soil, you can find up to 10 meters (approx. 33 feet) of these filaments. These networks increase the root exploration surface by up to 100 times to capture water and nutrients.
Architecture of fungal mycelium. The architecture differs between strains and species. Networks imaged at the AMOLF Institute of Biophysics in Amsterdam.
Credit: Corentin Bisot - VU Amsterdam, AMOLF. Justin Stewart - SPUN Essential allies for climate and agriculture
Each year, these underground networks bury nearly one billion tonnes of carbon dioxide (approx. 1.1 billion short tons) in soils. This natural mechanism plays a major role in regulating the global climate. Without these fungi, some of the atmospheric carbon would remain suspended.
Wild grasslands concentrate 40% of this fungal biomass. Yet they are the least protected ecosystems. Their conversion to agricultural land is 4 times faster than that of forests. In cultivated areas, network density drops by nearly half compared to natural environments.
Mycorrhizal fungi under a microscope at the AMOLF Institute of Biophysics. The circular structures are spores. Color is modified for readability.
Credit: Tomás Munita Identified threats, possible solutions
Mechanical plowing physically destroys the filaments. Fertilizers and fungicides disrupt the relationship between plants and fungi. These practices reduce the soil's ability to store carbon and retain nutrients. Researchers call for better protection of remaining wild grasslands.
The team suggests drawing inspiration from less invasive agricultural methods, such as no-till farming or organic cultivation. Maintaining dense fungal networks would reduce fertilizer use while improving crop resilience to drought. Collaboration between scientists and farmers is considered a priority.
To go further: How do we measure invisible networks?
Researchers collected more than 16,000 soil cores from all continents. Each sample was analyzed to count fungal filaments. An imaging robot photographed over 300,000 hyphae (filaments) grown in the lab.
These local measurements were used to train a machine learning model. The model incorporates climate data, soil type, and vegetation type. It can thus predict fungal density where no sampling has taken place.
The resulting map has a resolution of one square kilometer (approx. 0.386 square miles). Only ice caps and areas without sufficient data are excluded.
Author of the article: Cédric DEPOND