Global density and biomass of arbuscular mycorrhizal fungal networks 

Stewart et al., 2026

Most species of plants form underground associations with arbuscular mycorrhizal (AM) fungi, which provide plant roots with nutrients in exchange for carbon. AM fungi form networks of hyphae that act as tubes spreading carbon and connecting plants, but the global scale of these networks is unknown because of the difficulty of observing them underground. Compiled field and experimental data on hyphal density and used machine learning to predict how AM density varies across the globe. They then predicted hyphal biomass using high-resolution image analysis of hyphal network length from two globally distributed fungal species grown on transparent media in the lab. The authors predicted a large and spatially variable extent of AM fungi across the globe.

Arbuscular mycorrhizal fungi form symbioses with ~70% of plant species, building hyphal networks that exchange nutrients for host-derived carbon. These tubular networks move ~1 billion metric tons of carbon per year into Earth’s soils. However, we have no quantitative understanding of the hyphal infrastructure required to carry out this resource transfer. We assembled data from 322 studies representing more than 16,000 soil cores across nine biomes and developed machine-learning models to predict hyphal densities globally. With robotic imaging of more than 300,000 hyphae, we calibrated a biomass model from our spatial predictions. We estimate that global topsoils contain 1.10 × 1017 ± 0.13 × 1017 SD kilometers of living hyphae, weighing ~300 ± 60 SD megatons, ~4- to 6-fold the biomass of humans. Our uncertainty analyses identified undersampled ecosystems that require additional empirical attention.

https://www.science.org/doi/10.1126/science.adu4373

Maps:

https://a-hidden-infrastructure.spun.earth/story/mycorrhizal-infrastructure-map

https://www.spun.earth/underground-atlas/mycorrhizal-biodiversity