A complementary study of network development was then presented by Luke Heaton, who discussed growth induced
mass flows. He explained that the translocation of resources within fungal networks is ecologically critical, but it is much
less well studied than transport in the other major multicellular kingdoms of life (Jennings 1987). In particular, he
noted that the relative roles of pressure driven mass-flows diffusion and active transport remain poorly understood.
The uptake of water and the maintenance of turgor pressure require an osmotic gradient between the hyphae and their
environment, but because aqueous fluids are incompressible, mass flows can only take place when water is able to exit
the translocation pathway through either localised exudation (e.g. Serpula lacrymans), evaporation, or by moving into a
region of new growth (Cairney 1992, Lew 2005). Growthinduced mass flow can be used to describe the last of these
phenomena (Heaton et al. 2010). The key idea here is that as the hyphal tips expand, the incompressibility of aqueous
fluids ensures that in the supporting mycelium, there must be a net flow of fluid from the sites of water uptake to the
sites of growth. To quantify the scale of growth-induced mass flows and gain insight into the developmental logic of fungal
networks, a mathematical model based on circuit theory has been developed, and applied to three empirical networks of
Phanerochaete velutina. Given a time series of networks where each edge has a measured volume, the model was
used to calculate a current for each edge. These currents reflect the minimal flow of material that is consistent with the
measured changes in volume, under the assumptions that: (1) the inoculum is the sole source of water and nutrients;
(2) the conductance of cords is proportional to their cross sectional area; and (3) the fluid follows the path of least
resistance. Cords that are predicted to carry larger currents were significantly more likely to increase in thickness than
the other cords (Fig. 2). Over three replica experiments the Spearman’s rank correlation coefficient between the volumes
predicted to have passed through the cords and the cord’s cross-sectional areas was 0.51. In contrast, the correlation
coefficient between the age of cords and their cross-sectional areas was only 0.21 (Heaton et al. 2010).
A complementary study of network development was then presented by Luke Heaton, who discussed growth induced
mass flows. He explained that the translocation of resources within fungal networks is ecologically critical, but it is much
less well studied than transport in the other major multicellular kingdoms of life (Jennings 1987). In particular, he
noted that the relative roles of pressure driven mass-flows diffusion and active transport remain poorly understood.
The uptake of water and the maintenance of turgor pressure require an osmotic gradient between the hyphae and their
environment, but because aqueous fluids are incompressible, mass flows can only take place when water is able to exit
the translocation pathway through either localised exudation (e.g. Serpula lacrymans), evaporation, or by moving into a
region of new growth (Cairney 1992, Lew 2005). Growthinduced mass flow can be used to describe the last of these
phenomena (Heaton et al. 2010). The key idea here is that as the hyphal tips expand, the incompressibility of aqueous
fluids ensures that in the supporting mycelium, there must be a net flow of fluid from the sites of water uptake to the
sites of growth. To quantify the scale of growth-induced mass flows and gain insight into the developmental logic of fungal
networks, a mathematical model based on circuit theory has been developed, and applied to three empirical networks of
Phanerochaete velutina. Given a time series of networks where each edge has a measured volume, the model was
used to calculate a current for each edge. These currents reflect the minimal flow of material that is consistent with the
measured changes in volume, under the assumptions that: (1) the inoculum is the sole source of water and nutrients;
(2) the conductance of cords is proportional to their cross sectional area; and (3) the fluid follows the path of least
resistance. Cords that are predicted to carry larger currents were significantly more likely to increase in thickness than
the other cords (Fig. 2). Over three replica experiments the Spearman’s rank correlation coefficient between the volumes
predicted to have passed through the cords and the cord’s cross-sectional areas was 0.51. In contrast, the correlation
coefficient between the age of cords and their cross-sectional areas was only 0.21 (Heaton et al. 2010).
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