Full Breakdown
New Global Map Shows Vast Arbuscular Mycorrhizal Fungal Network
6/12/2026, 4:19:14 AM
Background & Context
Arbuscular mycorrhizal (AM) fungi form hyphal webs that exchange nutrients and carbon with about 70 % of terrestrial plants. Their distribution was unknown. Evolutionary biologist Justin Stewart of SPUN and colleagues compiled 16,669 soil cores from studies worldwide. Machine-learning models produced the first map of AM fungal density and biomass, published in *Science* on 11 June 2026.
Scale & Statistics
The model estimates an average hyphal density of 237 feet per cubic inch (4.4 m cm?³) in topsoil. Laid end-to-end, the hyphae would span about 68 quadrillion miles (110 quadrillion km), ~10 % of Milky Way’s width. Grasslands have the highest density (355 ft in?³) and hold ~40 % of AM biomass. Total fungal carbon is ~300 megaton—four to six times human mass—and the networks move ~4 billion metric tons of carbon annually, ~11 % of 2021 fossil-fuel emissions. Cropland topsoil shows 47–50 % lower hyphal density than wild ecosystems.
Ecological and Climate Implications
Dense hyphal systems in undisturbed grasslands act as reliable carbon sinks, sequestering carbon deep in soils, stabilizing nutrients, and boosting plant drought tolerance and disease resistance, supporting biodiversity. Reduced fungal density in agricultural lands lowers soil carbon storage and raises nutrient-runoff risk.
Official Statements & Responses
Andrea Genre (University of Turin) called the map “urgently needed” for biodiversity conservation, management and climate mitigation. Edouard Evangelisti (Côte d’Azur University) called it a “major milestone” that makes “part of the invisible visible.” Stewart urged protection of wild grasslands amid rapid conversion to farmland. Toby Kiers (Vrije University Amsterdam) stressed the need to bring hidden fungal patterns to policymakers.
Criticism, Threats, and Gaps
The authors link lower hyphal density in croplands to fungicides, phosphorus and nitrogen fertilizers, and intensive tillage. Sampling is sparse in tropical rainforests and deserts, leaving uncertainty. No dissenting voices appear, but the agricultural impacts form a clear counter-argument to land-use practices.
Conflicting Reports & Gaps
The study reports cropland hyphal density as 47.3 % lower in one source and “roughly 50 % lower” in another. Carbon transport is cited as 4 billion metric tons and 4.3 billion tons CO2-equivalent in reports.
Verbatim Quotes
- “This is the most dense fungal forest on Earth, and they're under wild grasslands,” — Justin Stewart, Evolutionary Biologist, SPUN
- “People just aren’t paying attention to these ecosystems,” — Toby Kiers, Evolutionary Biologist, Vrije University Amsterdam
- “makes part of the invisible visible,” — Edouard Evangelisti, Plant Scientist, Côte d’Azur University
- “If they disappear, there’s going to be a lot more chemicals going into waterways,” — Toby Kiers, Evolutionary Biologist, Vrije University Amsterdam
What’s Next
The team will refine the map over five years as soil cores are added. Findings will be presented at the Desertification COP in Mongolia to guide policies protecting fungal hotspots and encouraging fungal-friendly agriculture.
