Growth-induced mass flows in fungal networks

Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimising the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive, biological transport networks.

💡 Research Summary

The paper investigates how the growth of cord‑forming fungi generates internal mass flows that sustain efficient transport throughout the mycelial network. The authors begin by noting that water uptake in fungi is often spatially separated from the growing hyphal tips, and because the aqueous cytoplasm is essentially incompressible, any local increase in volume must be compensated by fluid movement elsewhere. From this premise they formulate a physical model in which growth‑induced changes in cord volume act as sources or sinks of fluid, and the resulting flow field is the one that minimizes the total viscous dissipation required to move the fluid through the network of cords.

Mathematically the mycelium is represented as a graph whose nodes correspond to hyphal junctions and whose edges correspond to cords (tubes) characterized by length L, cross‑sectional area A, and a constant viscosity η. Assuming Newtonian flow, the hydraulic resistance of an edge is R = 8ηL/(πA³). For each node i the net inflow minus outflow must equal the measured rate of volume change dV_i/dt, which is obtained from time‑lapse imaging. The set of linear equations that couples node pressures to edge currents is under‑determined; the authors resolve this by imposing the principle of minimum viscous dissipation, i.e., they minimize Σ I²R over all edges subject to the volume‑conservation constraints. This yields a unique set of currents {I_ij} for any given snapshot of the network.

Experimentally, the authors cultivated Phanerochaete velutina on a transparent agar substrate and recorded high‑resolution images every six hours. An image‑analysis pipeline extracted the network topology, measured cord lengths and diameters, and calculated the temporal change in cord volume at each node. These data served as inputs to the model, producing predictions of flow speed (v = I/(A·ρ)) and the pressure gradient required to sustain the flow.

The model’s predictions matched independent measurements of cytoplasmic streaming speed (≈0.1–2 µm s⁻¹) and required pressure differences on the order of 10⁻³–10⁻² Pa, indicating that the mycelium can generate the observed flows without any active pumping mechanism. Moreover, cords that the model identified as carrying larger currents or higher velocities were significantly more likely to increase in cross‑sectional area over time, whereas low‑flow cords tended to shrink or disappear. This correlation suggests a feedback loop: faster flow reinforces cord thickening, which in turn lowers hydraulic resistance and further enhances flow.

The authors discuss the broader implications of these findings. The coupling of growth‑driven volume changes with the incompressibility of the internal fluid creates a rapid, quasi‑global redistribution of mass in response to local events. Consequently, flow velocity itself becomes a local signal that conveys information about a cord’s functional importance within the whole network. This mechanism mirrors principles observed in other biological transport systems, such as plant xylem development and vascular remodeling in animals, where mechanical or hydraulic cues guide structural adaptation.

In conclusion, the study demonstrates that fungal mycelia exploit basic physical constraints—fluid incompressibility and minimization of viscous work—to self‑organize into highly efficient, adaptive transport networks. The work bridges mycology, fluid mechanics, and network theory, offering a quantitative framework that could inform the design of synthetic transport systems, bio‑inspired materials, and strategies for controlling fungal spread in ecological or agricultural contexts. Future directions include extending the model to account for non‑Newtonian cytoplasmic rheology, anisotropic cord properties, and environmental stresses such as dehydration or nutrient limitation.