Traveling-wave strategy for plant-mycorrhizal trade*

Mycorrhizal fungi construct complex mycelial networks to collect and trade nutrient resources with plant roots. Like human-built commercial networks, these fungi face conflicting trade-offs in building networks that balance low construction costs with high geographic coverage and long-distance transport. Yet, how they navigate supply-chain design challenges is unknown. To monitor the construction of a living trade network, we built a custom-designed robot for high-throughput time-lapse imaging that could track >500,000 fungal nodes simultaneously. We then measured ~100,000 cytoplasmic flow trajectories inside networks, toward and away from roots. Our findings provide the first direct evidence that symbiotic fungi control network-level structure and flows to meet trade demands. However, the mechanisms by which an organism with such a diffuse networked anatomy achieves control of growth and transport remain entirely open. I will conclude by discussing the possibility that adaptive rearrangements of the network anatomy and transport could be understood as a physical learning problem.