The inducible plant immune responses that alter plant-herbivore interactions through time are well-elucidated. Despite that mycorrhizal fungi associate with 80% of the plants worldwide, however, it remains unclear how mycorrhizal fungi alter and shape inducible plant immune responses to herbivory. Given that mycorrhizal fungi often alleviate biochemical and nutritional constraints on plants, it is possible that mycorrhizae promote plant responses to herbivory and differentially alter herbivore performance and preference. Based on the known nutritional exchanges between mycorrhizae and plants, we predicted that herbivores would perform worse on mycorrhizae-incolated, herbivore-damaged plants due to promoted production of induced chemical defenses. We established an experiment that tested the independent and interactive effects of mycorrhizal inoculants (none, single species, mix) and past herbivory (included, excluded) on herbivore performance and preference. Specifically, we employed choice and no-choice assays with Spodoptera frugiperda on Solidago altissima. No choice assays involved raising S. frugiperda larvae on sterile, AMF- and commercial mix- inoculated plants. We conducted 36 hour choice assays in which S. frugiperda larvae could choose between leaves from plants undergoing different mycorrhizal and herbivory treatments. Here we present the results demonstrating how mycorrhizae and herbivory history influence herbivore performance and preference.
Results/Conclusions
Preliminary results indicate that herbivores perform better on plants grown with a diversity of mycorrhizal mutualists than plants inoculated with a single mycorrhizal species (p=0.014). Directly contrasting with our original predictions, herbivory history alters this pattern by suppressing the effects of mycorrhizal diversity (herbivory treatment x inoculation treatment, p = 0.017). Preliminary analysis demonstrates that naive herbivores performally equally as well on plants inoculated with a diversity of mycorrhizae as plants inoculated with a single species as long as the host plants had previously experienced herbivory (p = 0.17). Given the strong diversity effects without herbivory, and the subsequent loss of diversity effects with herbivory, our results suggest that there are complex interactions between below-ground mutualists and above-ground antagonists. To elucidate possible mechanisms for these patterns, we are analyzing foliar nutrition, as mycorrhizal mutualists may differentially alter herbivore performance through improved foliar nutritional value. For herbivore preference, preliminary results of choice assays within each inoculation treatment (none, single species, mycorrhizal mix) has not revealed a clear preference between undamaged leaves from herbivore-damaged and non-herbivore-damaged plants (p = 0.636).