Competitive Effect and Mechanisms of an Invasive Species, Japanese Knotweed (Polygonum cuspidatum) in the Riparian Plant Community of the Susquehanna River

Polygonum cuspidatum, Japanese knotweed, is an invasive exotic species from Asia. Originally introduced to North America as an ornamental plant, it has caused significant disruption to the native riparian plant communities of Pennsylvania. In the summer of 2014 we carried out field research in the riparian zone of the Susquehanna River adjacent to Bucknell University to identify native plants that are highly susceptible to competition from P. cuspidatum. Our current research is investigating the mechanism of this competition with a focus on the role of allelopathy, the release of chemicals that inhibit the growth of other plants. Allelopathy is thought to be one of the main mechanisms that allows P. cuspidatum to successfully compete with native plants. In the field study, several 2.5m by 0.5m plots were set up on both the upstream and downstream sides of patches of P. cuspidatum encountered along the river and divided into five 0.5m by 0.5m plots. In each plot, frequency of each species was recorded and a photo was taken from above. Impatiens pallida and Verbesina alternifolia may be highly susceptible to P. cuspidatum and are candidates for further study. We are conducting controlled studies in the lab that measure the effect on germination and growth of applying extracts from leaves and rhizomes of P. cuspidatum to the seeds of I. pallida and V. alternifolia. An additional study will be conducted in the field that measures the effect of either the full plant, only the below ground parts, or only the aboveground parts of Japanese knotweed on the other species in its community with a specific focus on the plants that were found to be highly susceptible to its presence