Time lapse: Tracking The Arbuscular Mycorrhizal Fungal Network Development

Original video: https://youtu.be/teI6tkesl8s

The arbuscular mycorrhizal (AM) symbiosis is arguably the most widespread symbiotic partnership in nature, forming in the roots of around 70% of terrestrial plant species that, in turn, dominate Earth’s biomass. AM fungi form complex mycelial networks of filamentous hyphae that are aseptate—meaning that their cells are not divided by internal walls. They form open conduits where carbon and nutrients are stored, and also flow dynamically through cytoplasmic streaming toward and away from host roots. These nutrient-rich networks can reach densities of 10 m cm⁻³ and underlie global carbon cycling.

The diverse trade behaviours enacted by mycorrhizal fungi are well documented, with research suggesting that fungal partners move and exchange resources in ways that can improve their access to host carbon. Although progress has been made in imaging mycorrhizal networks and exploring their cytoplasmic dynamics, their precise topology—and internal cytoplasmic flows—have never been quantitatively tracked across space and time. Models of AM network growth have depended primarily on coarser mycelial density data, which cannot resolve how AM fungi build and operate their networks to meet trade demands. This is surprising because the spatial and temporal context of resource movement is fundamental to AM symbioses: the fungal partner depends on plant roots for carbon, received as sugars and fats (that is, obligate biotroph). In return, the fungus must continuously provide nutrients (such as phosphorus) to the host by extracting and moving resources through filamentous networks. The spatial expansion of the fungal network leads to new opportunities for colonization and trade, as the network encounters new resources and roots.

To date, difficulties in simultaneously tracking dynamic topologies of mycorrhizal networks, while measuring their internal cytoplasmic flows, have precluded understanding how symbiotic fungi modulate their anatomical architecture and transport patterns to meet trade demands. To overcome these challenges, we built an imaging robot enabling time-resolved microscopy of network topologies in up to 40 in vitro root organ culture (ROC) plant–fungal replicates simultaneously (Methods). A typical experiment acquired 150 images per replicate every 2 h at ×2 magnification, with an image overlap of about 20%. This configuration enables imaging of full network graphs by constraining growth to two dimensions, but basic symmetry considerations suggest relevance for fungal growth in three-dimensional soils. Through computational image analysis, we extracted the full network graph at every timepoint and tracked every node (growing tips, hyphal branches and junctions) and every edge (hyphal segments between nodes) across time, assigning each element a unique identifier. A typical experiment tracked around 40,000 nodes per plate and about 500,000 nodes across replicates. Using element-by-element tracking, we created time-lapse videos of fungal trade routes and monitored architectural rearrangements across the symbiotic network, such as hyphal fusion (that is, anastomosis) and timing/location of spore formation.

This video shows the extracted skeleton of a fungal network as it develops over the first 112 hours of growth. The color of each hyphal segment in the network corresponds to the time at which it appeared, providing a visual representation of the network's growth chronology. This video also illustrates the detailed tracking of individual components within a fungal network over time. Each node (growing tips, hyphal branches, and junctions) is assigned a unique color label that is maintained throughout the video. Similarly, each edge (hyphal segment between nodes) is also color-coded based on its label, which remains consistent as long as its two end nodes remain the same. This element-by-element tracking allows for the monitoring of network dynamics and rearrangements. The scale bar indicates 1 mm.

Keywords: Arbuscular Mycorrhizal, Fungal Network Development, Time-Lapse, Mycelial Network, Hyphal Growth, Network Skeleton, Growth Chronology.

Citation:

Oyarte Galvez, L., Bisot, C., Bourrianne, P. et al. A travelling-wave strategy for plant–fungal trade. Nature 639, 172–180 (2025). https://doi.org/10.1038/s41586-025-08614-x

Published on: 26 February 2025

Attribution 4.0 International — CC BY 4.0 - Creative Commons