Abstract
Saprotrophic cord-forming basidiomycetes, with their mycelial networks at the soil/litter interface on the forest floor, play a major role in wood decomposition and nutrient cycling/relocation. Many studies have investigated foraging behaviour of their mycelium, but there is little information on their intelligence. Here, we investigate the effects of relative size of inoculum wood and new wood resource (bait) on the decision of a mycelium to remain in, or migrate from, inoculum to bait using Phanerochaete velutina as a model. Experiments allowed mycelium to grow from an inoculum across the surface of a soil microcosm where it encountered a new wood bait. After colonisation of the bait, the original inoculum was moved to a tray of fresh soil to determine whether the fungus was still able to grow out. This also allowed us to test the mycelium’s memory of growth direction. When inocula were transferred to new soil, there was regrowth from 67% of the inocula, and a threshold bait size acted as a cue for the mycelium’s decision to migrate for a final time, rather than a threshold of relative size of inoculum: bait. There was greater regrowth from the side that originally faced the new bait, implying memory of growth direction.
Highlights
Fungi are vital agents for organic matter decomposition, and carbon and nutrient cycling in forest ecosystems by virtue of their huge biomass, enzymatic ability, and efficient translocation of carbon and nutrients by mycelial networks [1]
If a newly encountered resource is sufficiently large compared with the inoculum, connecting cords thicken and non-connected mycelium regresses, resulting in a strong connection between inoculum and bait
The aims of this study were to (1) determine what conditions make a fungal mycelium decide to make its final move from an old inoculum to a new wood resource, and (2) test whether a fungal mycelium within an inoculum remembers the direction of a new resource bait to which it had been connected, if the cord connection between the inoculum and bait was completely destroyed
Summary
Fungi are vital agents for organic matter decomposition, and carbon and nutrient cycling in forest ecosystems by virtue of their huge biomass, enzymatic ability, and efficient translocation of carbon and nutrients by mycelial networks [1]. Cords are aggregations of many parallel-aligned hyphae, which are often differentiated internally, forming large networks at the interface of the litter layer and soil horizon in the forest floor, translocating carbon and nutrients efficiently [2,3,4]. When a wood block colonised by a cord-forming basidiomycete is placed as an inoculum on the surface of compressed soil, mycelium grows out from the inoculum onto the soil, colonising any new resources that it encounters. Similar patterns are seen on the forest floor [10], and there is evidence that mycelium sometimes completely abandons small resources [12]. The latter phenomenon has not been investigated experimentally
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