Effects of herbivory simulated by clipping and jasmonic acid on Solidago canadensis

Herbivory is likely to be an important factor in the evolutionary ecology of plants and especially of aggressive invasive species. Because in the introduced range experimental treatment with non-native herbivores is laborious and may be risky for native plants, simulated herbivory by removal of plant tissue and treatment with jasmonic acid, which is a natural elicitor of defences against herbivores, may be a suitable alternative in experimental studies. We studied the effects of removal of 50% of the leaf area by clipping and of spraying with jasmonic acid on growth, morphology, leaf physiology and reproduction of the invasive Solidago canadensis in Europe. The relative height growth rate was reduced (-11.9%) by clipping in the period of day 0-20 but increased (+13.5%) in the period of day 42-138 after start of the treatments. As a consequence, final heights did not differ between treatment and control plants. Clipped plants, however, had thinner stems (-12.2%) than unclipped ones. Plants that had been sprayed with jasmonic acid tended to have shorter stem internodes (-14.7%), a lower specific leaf area (-4.6%), and to delay flowering (+4.4 days) than plants that had not been sprayed with jasmonic acid. The biomass of inflorescences was reduced by both clipping (-43.2%) and spraying with jasmonic acid (-32.2%). Because each, clipping and jasmonic acid, alone only induced some but partly different responses observed in previous studies with natural herbivores, the combined application of both covers the full response spectrum better and should therefore be used as the most realistic simulation of herbivory.