Mycelial dynamics during interactions between Stropharia caerulea and other cord-forming, saprotrophic basidiomycetes.

•  Macroscopic mycelial interactions between Stropharia caerulea and four other cord-forming wood decomposer basidiomycetes (Phanerochaete velutina, Phallus impudicus, Hypholoma fasciculare and Agrocybe gibberosa) on nonsterile soil were quantified using nondestructive image analysis. •  Interaction development and outcome was species dependent. Once S. caerulea mycelium became fully confronted by nonself mycelia, extension usually ceased and mycelia formed (defensive) aerial ridges and/or (invasive) cords. P. velutina rapidly replaced S. caerulea, but with significantly (P < 0.05) reduced biomass and mass fractal dimension (DBM ). S. caerulea regressed, biomass, DBM and surface fractal dimension (DBS ) became significantly (P < 0.05) reduced. •  S. caerulea produced temporary defensive ridges against P. impudicus, the latter extending through and replacing S. caerulea mycelium, but with significantly (P ≤ 0.05) reduced biomass. S. caerulea and H. fasciculare deadlocked, the latter producing dense (high DBM ) noninvasive lateral mycelial fans resulting in persistent mycelial fronts. S. caerulea and A. gibberosa initially deadlocked, the latter completely encircling S. caerulea. In response, S. caerulea produced defensive mycelial ridges at the interaction margin, and fans extended over A. gibberosa. •  These results are discussed in relation to mycelial foraging strategies, mycelial morphogenesis and determinants of interaction outcome.