Invertebrate grazing during mycelial interactions

Saprotrophic cord-forming basidiomycete fungi are major agents of wood decomposition in woodland and support the decomposer food-web. Limited resource availability and the abundance of mycelium in soil leads to competition between fungi. These fungal interactions are aggressive involving reallocation of mycelial biomass, pigment formation, changes in gene expression and enzyme synthesis. Collembola are abundant mycophagous invertebrates in woodlands and affect fungal morphology and growth. Experiments investigated the effects of collembola grazing on fungal interaction progression and the effects of these interactions on collembola behaviour and mortality. In British woodlands, the collembola Folsomia Candida and Protaphorura armata are common as are the cord-forming fungi Hypholoma fasciculare, Phallus impudicus, Phanerochaete velutina and Resinicium bicolor. Pairwise interactions between these fungi were investigated in agar and compressed soil microcosms. Multiple genetic isolates of two of the fungi studied were also used. Fungal morphology was affected by collembola grazing in soil- but less so in agar- microcosms. In particular, when interacting with H. fasciculare, grazing of P. velutina mycelia accelerated growth over the opposing mycelium but reduced extension over soil. This was associated with an increased ability to colonise the wood resource of H. fasciculare. Grazing did not reduce the transport efficiency of P. velutina but the estimated cost of biomass production rose more steeply with increasing area than in ungrazed systems. Despite changes in progression, interaction outcome was not generally substantially altered by grazing. Collembola exhibited strong preferences for certain mycelia during interactions but showed a change in preference in others. Collembola mortality on fungal interactions in agar microcosms also varied with the species interacting. There was limited evidence of attraction of collembola to the fungal interaction zone. Overall, the results suggest that collembola grazing may have important impacts on fungal species assemblage and their ability to extend in search of new resources