Mowing mitigates the enhancement of nitrogen enrichment on grassland insect herbivory

Insect herbivory influences ecosystem nutrient cycling and energy flow, and is sensitive to global change drivers. Nitrogen (N) enrichment would stimulate grassland insect herbivory by increasing insect abundance and changing plant community. However, it remains unknown whether such impacts of N enrichment would depend on grassland management practices, such as mowing. With a field experiment in temperate steppe after eight years treatments, we examined the role of mowing in mediating the impacts of N addition on insect herbivory at both species and community levels. Nitrogen addition significantly increased insect herbivory at the community level from 2.55 % to 9.36 %, while mowing decreased that from 9.49 % to 2.42 %. The positive impacts of N addition on herbivory were much stronger under unmown than mown condition, resulting in a significant interaction between N addition and mowing. Nitrogen addition enhanced herbivory by reducing plant C:N and increasing insect abundance. In contrast, mowing showed opposing effects on those two variables, and consequently led to lower herbivory. Mowing reduced the magnitude of N-induced herbivory in grasslands. Our results demonstrate that grassland management status should be given full consideration when assessing the impacts of eutrophication on insect-mediated transfer of nutrients and energy between plant and insect communities.