Resource acquisition by the mycelial-cord-former Stropharia caerulea: effect of resource quantity and quality

Saprotrophic mycelial-cord-forming basidiomycetes, which extend between organic substrata on the forest floor, exhibit remarkable patterns of reallocation of biomass and nutrients when encountering new resources. These have been equated with foraging strategies, and differ between species, resources quality and quantity. Stropharia caerulea occupies more disturbed sites than the fungi previously examined, and the responses of its mycelial foraging systems were investigated non-destructively by image analysis. Resource quantity and quality affected extension rate, extra-resource biomass production and distribution, as quantified by box-count fractal dimension. When mycelia grew from 0.5 cm3 beech (Fagus sylvatica) wood inocula across compressed, non-sterile soil to 0.06–4 cm3 uncolonised sterile beech wood "baits" extension rate fell after contact with large wood baits but biomass production and mycelial distribution was unaffected. In contrast, extension rates of cord systems grown from 0.15 cm3U. dioica rhizome inocula to 0.1–1.2 cm3 rhizome "baits" were unaffected after contact with equal or larger sized baits, but biomass production rates fell and mass fractal dimension increased. Mycelial morphology was affected by inoculum age; systems grown from 84 day old 0.5 cm3 beech wood inocula took 10 days longer achieving the fractal values of systems developing from 22 day old inocula. Foraging strategies and resource relations of mycelial cord systems are discussed.