Saprotrophic cord systems: dispersal mechanisms in space and time

In natural terrestrial environments, nutrients are often patchily and sparsely distributed, and the microclimate is constantly changing both temporally and spatially. To survive, fungi must be able to transfer to a new resource before the nutrient supplies in their current food base are exhausted. While the majority of fungi propagate as spores, some basidiomycetes can grow out of a resource as mycelium in search of new resources. The mycelium of these fungi typically aggregates to form linear organs, termed cords or rhizomorphs, that ramify at the soil–litter interface in forests, interconnecting disparate litter components to form extensive (many square meters or even hectares), long-lived (many years) systems. These mycelial systems form effective dispersal mechanisms in space and time. This article reviews the two main, but not mutually exclusive, mycelial dispersal (resource capture) strategies: (1) a “sit and wait” strategy, whereby a large mycelial network waits for resources to land on it and then actively colonises those resources; and (2) growing and searching actively for new resources. The way in which mycelia balance exploration and nutrient transport, and robustness to damage, against “cost” of production and speed with which an area can be colonised, is explored using techniques borrowed from graph theory and statistical mechanics.