Global Map Uncovers Extensive Underground Fungal Network: Insights into Mycelium and Ecosystem Health

Below the Earth’s surface lies an extensive, carbon-rich network of fungi interlinked with plant roots, extending to a staggering 110 quadrillion kilometers. This intricate system forms part of our planet’s mycelial network, which facilitates nutrient exchange and climate regulation.

Arbuscular mycorrhizal fungi comprise an ancient group of soil fungi critical to most terrestrial ecosystems. These fungi create symbiotic relationships with approximately 70% of the Earth’s plant species, providing essential nutrients and water in exchange for carbon. “Plants may be seen as the saviors of fungi, but in reality, these fungi are equally vital for plant survival,” states Justin Stewart from the Association for Underground Network Protection. “Any plants not engaging in symbiosis with arbuscular mycorrhizal fungi are outliers in the plant kingdom.”

Recognizing the crucial role of fungi, Stewart and his team aimed to quantify this hidden ecosystem. “We posed the question: Can we map Earth’s subterranean circulation system?” says team member Toby Kiers, also with the Underground Network Protection Association.

The researchers analyzed data from 16,000 soil samples worldwide derived from 322 prior studies. They also employed robotic imaging to measure over 300,000 fungal threads cultivated in a laboratory, helping to estimate total biomass and carbon content within the network. The gathered data allowed them to extrapolate these estimates across deserts, tundras, forests, and regions lacking direct measurements.

The findings indicate that the arbuscular mycorrhizal fungi network sequesters around five times more carbon than all living humans combined. “These fungi play an indispensable role in various Earth functions,” notes Stewart. “For instance, they help sequester carbon underground, which is crucial for addressing climate change.”

Approximately 40% of the global arbuscular mycorrhizal fungi reside in grassland ecosystems, particularly in areas like South Sudan, the Florida Everglades, and the Tibetan Plateau. This situation raises concerns, as agricultural expansion poses a threat to these ecosystems.

In agricultural settings, fungal populations are significantly diminished, with network density reduced by about 50% in heavily cultivated soils compared to uncultivated ecosystems, despite having an abundance of plants. This decline is primarily due to fungicides that directly kill fungi, soil tillage that disrupts fungal networks, and excessive fertilizer use that hinders the critical nutrient and carbon exchanges that sustain symbiosis.

Last year, Laura Carter and researchers at the University of Leeds discovered that azole antifungals—chemicals commonly used to combat fungal crop diseases—can reduce mycelial density by approximately 70%, and beneficial fungal colonization of plant roots by up to 80%. This raises alarms about contemporary agricultural practices potentially endangering vital fungal allies. “Promoting arbuscular mycorrhizal fungi isn’t just an ecological concern; it offers practical benefits for enhancing soil health, resilience, and long-term crop yields,” emphasizes Carter.

Stephen Allison, a professor at the University of California, Irvine, expressed deep concern regarding the shrinking fungal network beneath farmlands: “With the biomass being severely reduced, our crops may be deprived of essential advantages like nutrient availability, drought resistance, and carbon storage.”

Nonetheless, there are opportunities for recovery. With the scale of fungal loss quantified, strategies can be developed to restore fungal biomass. “Farmers can introduce fungal spores back into the soil,” suggests Allison. “This research prompts an examination of farming practices, such as reducing cultivation and fertilizer applications.”

While the study highlights a vast fungal network, Stewart clarifies that this does not imply a universal “wood wide web,” a theoretical subterranean network for plants to exchange resources and information. “Our research focused on the sheer number of fungal threads across the globe, rather than proving they form a continuous network,” he states.

In tandem with this study, researchers unveiled an interactive map detailing the global distribution of fungal networks, offering unprecedented insights. Kiers intends to present these findings to policymakers at the upcoming United Nations Desertification Summit in Mongolia this August.