Herbivory and plant-soil feedbacks (PSFs) are ubiquitous processes, each with strong effects on plant communities and ecosystem processes. Yet little is known about the interactive effects of herbivory and PSFs. Such interactions might play a strong role in shaping native-invasive plant dynamics. For example, plant invasion success is thought to be enhanced both by escape from enemies, including specialist herbivores, and by positive PSFs, suggesting that herbivory x PSF interactions could be important. The purpose of this study was to determine whether an interaction between herbivory and PSFs influences an invasive species’ PSF advantage. In this full reciprocal PSF study conducted under greenhouse conditions, experimental communities of three native plants common to eastern U.S. woodlands (Elymus hysterix, Solidago flexicaulus, and Aster lateriflorus) and monocultures of the invasive liana Euonymus fortunei were established. In phase I of this study, the vegetation treatments were assigned to two herbivory treatment groups, unclipped controls and herbivory simulated by clipping, imposed for a three-month period. In phase II, conditioned soils from phase I were used to grow native communities, Euonymus monocultures, and native community-Euonymus mixtures using a pairwise PSF design. Above and belowground biomass was measured after another three months of growth.
Results/Conclusions
When phase I soils were conditioned in the absence of simulated herbivory, results indicated strong positive feedback promoting invasive growth: Euonymus productivity was higher, whereas native community productivity was lower, in soil conditioned by conspecifics relative to heterospecifics. For a Euonymus enemy escape scenario, conditioning soils with simulated herbivory reduced the strength of this positive feedback, because native community productivity markedly increased in soils conditioned by conspecifics exposed to simulated herbivory. The legacy effect of simulated enemy escape in reducing positive feedback was similar when Euonymus and the native community were grown in competitive mixture. These results indicate that herbivory can influence PSF dynamics between native and invasive plants. In particular, herbivory can reduce the positive feedback advantage exhibited by an invasive species of eastern U.S. woodlands.