Plant-microbe interactions in response to grassland herbivory and nitrogen eutrophication

Plant-soil feedback is increasingly recognized as a vital framework to analyze multi-trophic interactions involving herbivores, plants and microbes, but research is still lacking on understanding such feedback in the context of global change. In grasslands, patterns of herbivory are expected to be affected by global change, further modifying existing plant-soil feedbacks. We tested this by evaluating the individual and combined impacts of aboveground herbivory by a generalist leaf-chewer and nitrogen (N) eutrophication, simulating elevated N deposition, on soil microbial communities and root colonization of arbuscular mycorrhizal fungi and related these to existing data on plant functional types and community composition. We found that colonization of arbuscular mycorrhizal fungi in the plant roots responded differently to treatments depending on host plant species in patterns consistent with the changes in the plant community composition and biomass. Further, the effect of aboveground herbivory on plant-soil interactions was comparable and even exceeded that of N-eutrophication, with the additive effects of herbivory and N-eutrophication on the soil microbiome being stronger than each factor separately. Our results suggest that plant-soil feedback in response to N-eutrophication is contingent on biotic variables such as herbivory and plant species, and that biotic and abiotic disturbances may have additive effects on the soil microbiome structure.