Epsilon Open Archive

Abstract

Herbivorous insects can infuence grassland ecosystem functions in several ways, notably by altering
primary production and nutrient turnover. Interactions between above- and belowground herbivory
could afect these functions; an efect that might be modifed by nitrogen (N) addition, an important
global change driver. To explore this, we added above- (grasshoppers) and belowground (wireworms)
insect herbivores and N into enclosed, equally composed, grassland plant communities in a fully
factorial feld experiment. N addition substantially altered the impact of above- and belowground
herbivory on ecosystem functioning. Herbivory and N interacted such that biomass was reduced under
above ground herbivory and high N input, while plant biomass remained stable under simultaneous
above- and belowground herbivory. Aboveground herbivory lowered nutrient turnover rate in the
soil, while belowground herbivory mitigated the efect of aboveground herbivory. Soil decomposition
potential and N mineralization rate were faster under belowground herbivory at ambient N, but
at elevated N this efect was only observed when aboveground herbivores were also present. We
found that N addition does not only infuence productivity directly (repeatedly shown by others), but
also appears to infuence productivity by herbivory mediated efects on nutrient dynamics, which
highlights the importance of a better understanding of complex biotic interactions.