Flow with the Grow

In order to remain metabolically active, living things require a source of energy, and a regular supply of molecules of various kinds. As living things are composed of cells, large organisms inevitably face a fundamental challenge: they need to supply all of their component cells with the resources needed for survival. Mammals have cardio-vascular systems, plants have xylem and phloem, but how do fungi tackle the fundamental transport challenge? Compared to the other major kingdoms of multi cellular life, transport in fungi is poorly understood. This is somewhat surprising, as transport in fungi is an ecologically critical process. Fungi are an essential component of soil: without fungi leaf litter would not degrade, and many fungi form foraging networks which circulate carbon, nitrogen and phosphate. If a fungus grows, that increase in volume must come from somewhere: if the source of new volume is distant from the growth then this must create flows in the network. Because the volume is mostly water, which here is effectively incompressible, growth in one part of the network will be rapidly coupled to the rest. We suggest that fluid flows associated with growth might themselves be the major form of long-range transport in fungi. To investigate transport in fungi and the developmental logic of fungal networks, we photographed growing fungal networks, and digitized the images to produce a sequence of matrices that describe how the networks change over time. For each sequence of networks we identify a set of fluid flows which are as small as possible whilst being consistent with the observed changes in volume. We found that those parts of the network that were predicted to carry a large current typically thickened over time, while other parts of the network became thinner, or were consumed by the fungi in order to fuel further exploratory growth. So our crude idea (that flows are directly coupled to growths) did seem to be, at least partly, consistent with the data. You'll find our paper "Growth-induced mass flows in fungal networks" here and in its journal version (free, from Nov 2011, at the Proceedings of the Royal Society B) here. The Institute for Science, Innovation and Society did a blog on this article as well. Luke and Nick