A groundbreaking global digital map has for the first time unveiled the colossal scale of fungal networks hidden beneath the Earth's surface, revealing their critical importance for both plant life and the planet's climate. These vast, carbon-rich networks, estimated to stretch for 110 quadrillion kilometres, form intricate connections with plant roots, acting as a vital underground circulatory system.
Known as arbuscular mycorrhizal fungi, this ancient group forms symbiotic relationships with approximately 70% of the world's plant species. In this mutually beneficial exchange, the fungi supply plants with essential nutrients and water, while receiving carbon in return. Justin Stewart from the Society for the Protection of Underground Networks highlighted their significance, stating that these fungi are effectively the 'saviours of plants'.
To quantify this previously underestimated infrastructure, researchers analysed data from 16,000 soil samples collected worldwide across 322 previous studies. They also used advanced robotic imaging to measure over 300,000 fungal threads in laboratory settings, allowing them to estimate the total biomass and carbon stored within these networks. This data was then used to extrapolate estimates across diverse environments, including deserts, tundra, and forests, where direct measurements were scarce.
The findings indicate that these global fungal networks harbour a mass of carbon equivalent to approximately five times that of all living humans combined. This substantial carbon storage capacity underscores their vital role in regulating the planet's climate by drawing carbon underground. However, the study also raised concerns, estimating that around 40% of the world's arbuscular mycorrhizal fungi reside in grassland ecosystems, many of which are rapidly being converted into farmlands.
Further analysis revealed a significant reduction in fungal presence in croplands, with large-scale agricultural soils exhibiting network densities around 50% lower than those in uncultivated ecosystems. This decline is attributed to practices such as fungicide use, which directly kills fungi; tilling, which disrupts their networks; and heavy fertiliser application, which can undermine the nutrient-for-carbon trade essential for the symbiosis. Dr Laura Carter from the University of Leeds, UK, whose previous research showed azole antifungals cut fungal density by 70%, noted that current agricultural practices may be undermining a key natural ally for crops.
Steven Allison at the University of California, Irvine, expressed particular concern over the depleted networks in croplands, suggesting that agricultural crops may be missing out on crucial benefits like enhanced nutrient access, drought resilience, and carbon storage. However, he also pointed to a positive aspect: by quantifying the scale of these losses, researchers can now design targeted interventions, such as adding fungal spores to soils or encouraging farmers to adjust practices like reducing tillage or fertiliser use, to rebuild fungal biomass and improve soil health.