PALATABILITY OF MICROFUNGI TO SOIL ARTHROPODS IN RELATION TO THE FUNCTIONING OF ARBUSCULAR MYCORRHIZAE

We investigated the feeding preferences of six species of mites and co llembolans for three fungi commonly associated with roots of Acer sacc harum (Glomus macrocarpum, Alternaria alternata and Trichoderma harzia num), from a maple-forest soil in southern Ontario, Canada. Experiment s were also conducted in vitro to determine animal feeding responses t o (1) increasing quantities of hyphal biomass, (2) the presence of roo t vs. litter fungal substrates, and (3) hyphae of different widths of Glomus macrocarpum. The results indicate that arthropods prefer to gra ze in the litter region rather than in the deeper soil layers. Under i deal moisture/temperature conditions, animals are forced to the lower regions by interspecific interactions. They prefer to graze on hyphae of conidial fungi rather than on those of arbuscular mycorrhizal fungi . When arbuscular mycorrhizal fungal hyphae are grazed, there is a cle ar preference for the narrower hyphae, which are those further away fr om the root. The thicker hyphal segments, commonly found connecting '' absorptive hyphal fans'' to roots, were less preferred. These data are not consistent with the hypothesis that microarthropods are detriment al to arbuscular mycorrhizal associations, and suggest that Glomalean fungi may have evolved mechanisms to deter grazing by microarthropods.