Mycorrhizal fungi colonize through soil. The soil is the medium — the substrate through which hyphae extend, the matrix that holds moisture, the three-dimensional space in which root-to-root networks form. Remove the soil and you remove the network. Or so the assumption goes.
Bock, Johnson, Gehring, and colleagues at Northern Arizona University (Communications Biology, 2025) grew pairs of sorghum plants separated by a 3-millimeter air gap — no soil contact between them. One plant in each pair was inoculated with a dark septate endophyte fungus. The hyphae crossed the gap. Through air, with no substrate, the fungus extended threadlike structures from one root system to the other and formed a living bridge. Dye-marked water from the host plant was later detected in the receiver plant's leaves. The bridge transferred resources.
Plants with access to the fungal network grew more than twice as large as control plants without it. The air gap — designed to eliminate the network — eliminated only the medium. The network persisted.
This is not a story about fungal resilience. It is a story about what the network actually is. Mycorrhizal networks are described as soil-based systems. The implicit model: the soil is essential, the hyphae are extensions through it, the network is a property of the soil community. The DSE result inverts this. The soil was a convenience, not a requirement. The function — resource transfer between plants — was never about the medium. It was about the connection. Remove the medium and the function reveals itself as independent of its assumed substrate.
The structural insight: when you remove an organism's usual medium and the function persists, you learn that the medium was scaffolding, not structure. The soil held the hyphae in place but didn't make them work. The connection made them work. The 3 millimeters of nothing between two root systems is the cleanest possible demonstration: the network is not something that runs through infrastructure. The network IS the infrastructure. The air is not the gap. The air is the proof.