A recent study published in Nature highlights how researchers used a custom-built robotic system for high-throughput imaging to uncover how mycorrhizal fungi develop highly efficient nutrient-trading networks with plant roots.
Study: A traveling-wave strategy for plant–fungal trade. Image Credit: lego 19861111/Shutterstock.com
These fungi, which have evolved over 450 million years, construct self-regulating, wave-like networks that optimize exploration, resource transport, and efficiency. The findings reveal that fungal networks expand with minimal carbon investment while maintaining transport efficiency and adapting through loops and widened pathways—offering valuable insights into symbiotic supply-chain principles shaped by natural selection.
Background
Arbuscular mycorrhizal (AM) symbiosis, present in 70 % of terrestrial plants, is one of the most ecologically significant partnerships in nature. AM fungi form extensive mycelial networks that facilitate nutrient and carbon exchange with plant roots, playing a key role in global carbon cycling and plant biomass production.
These networks, made up of aseptate hyphae, enable dynamic cytoplasmic streaming of resources, but their precise topology and internal flow dynamics have remained largely unknown.
While previous research has documented the trade behaviors of AM fungi, studies have been limited by coarse mycelial density data, failing to capture the spatial and temporal dynamics of network formation and operation. This gap is particularly significant given that the fungal partner relies on host-derived carbon while continuously supplying nutrients such as phosphorus, necessitating efficient network expansion and resource transport.
To overcome these limitations, researchers have developed a high-throughput imaging robot capable of time-resolved microscopy, allowing them to simultaneously track network topologies and cytoplasmic flows in up to 40 plant–fungal replicates.
By analyzing over 500,000 network nodes, they quantitatively assessed fungal trade routes, architectural adjustments, and flow dynamics. This innovative approach provided an unprecedented look at the design principles governing symbiotic nutrient exchange networks shaped by evolution.
Self-Regulating Travelling Waves
The study identified a self-regulating traveling wave pattern in fungal growth. Using high-throughput imaging and computational analysis, researchers observed that fungal networks expand through a leading pulse of growing tips, followed by densifying hyphal filaments that stabilize at a low, constant density. Wave speed is driven by fast-growing "puller" tips, while density is controlled by branching and anastomosis (hyphal fusion).
This strategy ensures a balance between exploration, nutrient acquisition, and carbon trade, enabling efficient resource exchange with minimal carbon expenditure.
A mathematical model, the Branching and Annihilating Range Expansion (BARE) wave model, confirmed that AM fungi prioritize spatial exploration over densification—aligning with their symbiotic function. Experimental data showed that as fungal networks expand, phosphorus absorption increases, creating depletion zones that advance with the wavefront, optimizing nutrient uptake.
Automated tracking revealed that AM fungi maintain about 30 % of their network length as nutrient-absorbing structures (BAS), which enhances phosphorus uptake. Meanwhile, runner hyphae (RH) transition from exponential to quadratic growth. Loops formed through anastomosis further improve transport efficiency and robustness.
Graph theory analysis showed that these networks maintain stable transport efficiency towards plant roots while increasing overall efficiency over time, facilitating continued exploration and connection with new host plants. Notably, hyphal widths correlated with betweenness centrality (BC), suggesting that fungi modulate cross-sectional dimensions to support greater nutrient flow in central pathways.
High-resolution imaging of cytoplasmic flow revealed bidirectional particle movement, with speeds decreasing near growing tips (where diffusion dominates) and increasing in central, high-BC hyphae, optimizing transport efficiency. These findings indicate that AM fungi use a sophisticated, topology-informed strategy to optimize symbiotic trade, balancing exploration, nutrient absorption, and transport efficiency while minimizing carbon costs.
Growth and Transport in AM Fungal Networks
To analyze fungal network growth, researchers used Ri T-deoxyribonucleic acid (T-DNA) transformed carrot root cultures colonized by different AM fungal strains. Split Petri plates allowed hyphal growth without root interference, while a modified Strullu–Romand (MSR) medium with low phosphate levels encouraged colonization. The impact of myristic acid on fungal growth was also examined. Growth was monitored over two months under controlled conditions.
High-resolution imaging and image processing classified hyphae as either RH or BAS, while tracking anastomosis and branching events to understand network formation. Colony expansion rates were measured using convex hull radii, with puller hyphae identified at the growth front.
Cytoplasmic flow was assessed using high-magnification video analysis and deep learning tools (KymoButler). Flow speeds increased from 2–5 micrometers per second (µm/s) in the early days of growth to 45 µm/s after 2.5–3.5 days, with maximum speeds observed near growing tips. Kymographs visualized flow directionality, while spatial mapping linked flow speeds to tip distances.
Conclusion
This study provides new insights into how AM fungi construct self-regulating, wave-like networks to optimize nutrient trade with plant roots. By leveraging a high-throughput imaging robot and computational analysis, researchers demonstrated that AM fungi effectively balance exploration, resource transport, and efficiency through branching, anastomosis, and topology-informed flow modulation.
The use of robotics allowed for an exceptional level of precision in tracking fungal network dynamics, revealing how these organisms optimize their symbiotic trade strategies. The traveling-wave expansion strategy enables fungal networks to grow efficiently while minimizing carbon costs. Additionally, loops and widened pathways enhance adaptability and transport robustness.
These findings highlight not only the evolutionary sophistication of AM fungal networks but also the power of advanced imaging technologies in uncovering nature’s complex biological systems.
Journal Reference
Oyarte Galvez et al., 2025. A traveling-wave strategy for plant–fungal trade. Nature. DOI:10.1038/s41586-025-08614-x https://www.nature.com/articles/s41586-025-08614-x
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