Land use intensity modulates the impact of root herbivores on plant interactions with above- and below-ground organisms

Root herbivory can influence plant interactions with other organisms by systemically affecting plant morphology and chemistry. Strength and direction of this influence may depend on environmental factors such as land use intensity in managed systems. We established local Plantago lanceolata plants with and without root feeding Agriotes spp. larvae (Coleoptera, Elateridae) in their root system in grasslands of different management intensity. We then determined root herbivore impacts on plant interactions with invertebrate shoot herbivores and root fungi. Root herbivory reduced length and biomass of P. lanceolata roots independent of land use intensity. Root colonization by non-mycorrhizal fungi increased with increasing cattle grazing intensity, but was unaffected by root herbivory. The root herbivore impact on root colonization by arbuscular mycorrhizal fungi depended on cattle grazing intensity. Root herbivores increased colonization under low but reduced colonization under high grazing intensities. Root herbivory affected P. lanceolata interactions with shoot herbivores, as indicated by increased leaf damage in the presence of root herbivores. The increase, however, declined with increasing mowing frequency. We conclude that land use intensity may determine the net effect of root herbivory on plant performance in managed systems.