Arbuscular Mycorrhizal Fungal networks in the spotlight

By Corentin Bisot, Vrije Universiteit Amsterdam

Arbuscular mycorrhizal fungi use plant-derived carbon to build extensive underground networks of filaments, called hyphae, that can stretch for meters through the soil. These networks are ubiquitous in underground ecosystems, measuring over meters per cubic centimeter of soil. Their detailed structure has however never been fully resolved.

In our work, we built a custom microscope capable of capturing month-long timelapses of growing fungal colonies in controlled conditions. To analyze this large amount of data (100s of Terabytes), we developed an image-processing pipeline that tracks the movement of millions of hyphal tips, the growing part of fungal hyphae.

We find that these tips collectively behave as a travelling wave, forming a propagating front that leaves behind a well-structured network that coats the grown-through space surprisingly evenly. This network is crucial for nutrient acquisition, as many plants rely on this symbiosis for a significant portion of their mineral intake. Striking a balance between dense coverage and outward expansion appears to be a carbon-efficient strategy to supply nutrients while also exploring for new host plants.

However, carbon and nutrients must flow in opposite directions—carbon from the plant to the fungi, and nutrients (nitrogen, phosphorous, etc) back to the plant. By zooming in on individual hyphae, we observed bidirectional flows, with resources moving both ways inside single tubes. These flows varied over time and space, suggesting a finely tuned system aligned with the needs of each organism.

This research opens new questions: How do these fungi balance network growth and resource exchange? And what physical mechanisms drive such coordinated bidirectional flows? We are just beginning to uncover the hidden dynamics of this fascinating underground world.

Because the soil is opaque, organisms that live there are by nature invisible. By bringing them to the light of the microscope, we hope that their beauty can also help protect them.

Highlighting soil biodiversity and bringing its stunning intricacies to public awareness is a central mission of our team. Toby Kiers founded the Society for the Protection of Underground Networks (SPUN), spearheading global expeditions to document and protect soil biodiversity. Additionally, thanks to captivating artwork by Loreto Oyarte Galvez, our work reached a broader audience through a feature in The New York Times. Corentin Bisot further enhances public engagement by developing the Living Soils Workshop, designed to share the wonders of soil ecosystems with communities worldwide.