In a series of greenhouse experiments, we examined the influence of below-ground herbivory by larvae of the Japanese beetle Popillia japonica Newman (Coleoptera: Scarbaeidae), and fungal endophyte infection on individual species performance and competition between the common forb Taraxacum officinale (dandelion) and two species of cool-season perennial turfgrasses Lolium perenne L. (perennial ryegrass) and Festuca araundinacea Schreb. (tall fescue). We hypothesized that because endophyte-mediated defensive compounds are mainly confined to above-ground plant tissues, endophyte-infected plants would not experience any significant competitive advantage in the presence of below-ground herbivory. Furthermore, we hypothesized that the influence of herbivory would vary through time in accordance with the life cycle of the herbivore. Burrowing activity associated with Japanese beetle oviposition increased tiller (grass) and leaf (dandelion) production, and above-ground biomass production in most cases through enhancing water infiltration and soil microbial activity. However, increased plant growth early in experiments did not compensate for damage caused by larval feeding. After five months, herbivory significantly reduced the number of tillers per plant, and above- and below-ground biomass production in both grasses, regardless of endophyte infection, in pure stands and in mixtures with dandelion. In turn, dandelion above-ground biomass and leaf production were often higher in herbivore treatments. Results indicate that endophyte infection can have variable effects on competition between grasses and dandelion and that below-ground herbivory can provide a competitive edge to dandelion. However, below-ground herbivory does not appear to affect endophyte-infected and uninfected plants differentially in this regard.
Keywords: tall fescue, perennial ryegrass
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