Grazing by collembola affects the outcome of interspecific mycelial interactions of cord-forming basidiomycetes

While there is a plethora of studies on the effects of invertebrate grazing on mycelia, including several studies on saprotrophic cord-forming basidiomycetes, there is little information on the effects of grazing on mycelial interactions. The study compares the progress and outcomes of interspecific mycelial interactions between Hypholoma fasciculare, Phallus impudicus, Phanaerochaete velutina and Resinicium bicolor when grazed by the collembola Folsomia candida or Protaphorura armata in agar culture and trays (24 × 24 cm) of non-sterile soil. In ungrazed systems results were broadly consistent with previous studies, though there were few instances of deadlock, and a clear transitive (A > B > C) hierarchy could not be discerned. Instead, there was an intransitive hierarchy (i.e., A > B, B > C but C > A). Additionally, in agar culture, there were considerable differences in combative ability of four different strains of H. fasciculare. Collembola grazing had major effects on mycelial interactions. F. candida grazing altered both the outcome and progression of half of the fungal interactions studied, while the less active P. armata had almost no discernable effects on fungal interactions. Grazing by F. candida affected mycelial extension rate in five of the interaction combinations, some increasing, others decreasing. In grazed systems of P. velutina interacting with H. fasciculare, extension rate of the former was much more rapid over the opponent than over soil. Not only did grazing affect mycelial interactions, but interactions affected grazer activity; H. fasciculare was grazed in areas where it was interacting with P. velutina mycelium, but less so elsewhere. By altering the outcome of mycelial interactions and mycelial extension rate, collembola grazing may alter the distribution of cord-forming fungi on the forest floor, and may also play a role in maintaining the diversity of fungal species. The differences in combative ability of different strains of a species imply an even more complex scenario in the natural world