Ankara: Underground networks formed by beneficial fungi extend roughly one billion times the distance between the Earth and the Sun, making them one of the planet's largest living structures and a crucial component of the global carbon cycle, according to a new study.

According to Anadolu Agency, an international team of researchers from Vrije Universiteit Amsterdam and the AMOLF Institute produced the first global map of arbuscular mycorrhizal fungal networks, which form symbiotic relationships with around 70% of all plant species.

These fungi exchange water and nutrients for carbon produced by plants, forming underground filament networks known as hyphae that help sustain ecosystems worldwide. The researchers estimate the total length of these living fungal networks in the planet's topsoil at about 110 quadrillion kilometers, or approximately 1 billion astronomical units.

To produce the map, scientists compiled data from more than 16,000 soil samples collected across nine global biomes and developed machine-learning models to estimate fungal density in regions that had not been directly sampled. The biomass estimates were calibrated using more than 300,000 laboratory measurements of fungal filaments.

The study estimates that the living fungal networks contain about 300 million tons of carbon, equivalent to four to six times the total carbon stored in all living humans. Researchers said the fungi transport around one billion tons of carbon from plants into soils every year, helping store carbon and supporting long-term soil health.

Grasslands were identified as the world's richest fungal ecosystems, accounting for roughly 40% of global fungal biomass. Particularly dense underground networks were found in the Sudd wetlands of South Sudan, the Everglades in Florida, and the Tibetan Plateau.

By contrast, agricultural soil contained significantly fewer fungal networks. The researchers found fungal densities in croplands were, on average, about 47% lower than in non-cultivated soils, which they linked to intensive farming practices such as fertilizer use and fungicide application.