Effects of herbivory, competition, and disturbance on a wetland plant community with emphasis on the dominant aquatic macrophyte, Nymphae odorata Aiton

The importance of herbivory, competition, and disturbance may differ within and between terrestrial and wetland ecosystems. Separate field and greenhouse experiments were performed to determine how these biotic interactions influenced the performance of a dominant macrophyte, Nymphaea odorata , and how the deep-water marsh community in which it occurs responded to physical disturbance.; During a two-year exclosure study in the field and a two-year greenhouse experiment, the effects of grazing on N. odorata growth and production were quantified to determine if moderate grazing affected plant performance as predicted by the grazing optimization hypothesis. Results tended to support the grazing optimization hypothesis, although increased aboveground growth in response to herbivory may have been at the expense of belowground growth.; During another experiment, N. odorata performance was quantified when growing alone and in mixture with a similar species, Nuphar advena. Interspecific competition between these two species was negligible, suggesting that other factors were more important for regulating N. odorata. Despite the lack of competition as a main effect, competition intensity tended to decline with increasing productivity, which is different from patterns frequently documented in terrestrial ecosystems.; To examine the contribution of seed banks to the formation of distinct plant assemblages after a physical disturbance, plant percent cover on and off floating islands was assessed in the field. A controlled greenhouse seed bank experiment in which water levels were manipulated was also conducted. Emergent plants dominated floating islands, which were characterized by localized declines in inundation, whereas N. odorata dominated undisturbed sites. Assemblages in the greenhouse experiment differed among water level treatments in a manner consistent with differences observed in the field. This suggests that floating island formation temporarily altered inundation favoring the germination of a more species-rich, emergent plant assemblage, and may be one mechanism maintaining otherwise rare plant populations. These experiments suggest that herbivory and disturbance are more important than competition for regulating N. odorata and for influencing the surrounding deep-water marsh community at this site.