Competition between two floating-leaved aquatic plants.
Water chestnut (Trapa natans L.) is a notorious aquatic invasive species invading wetlands and waterways of the northeastern United States. In the Great Lakes watershed, specifically Lake Ontario coastal wetlands, water chestnut grows in areas similar to the native white water lily (Nymphaea odorata Aiton). To understand better the competitive interactions these species may have, they were grown in mesocosms in a factorial design to simulate varying levels of invasion. Biomass, percent cover, number of rosettes or leaves, and specific leaf area of both species, and seed production of T. natans were measured and analyzed. Relative growth rate (RGR) was also calculated. These data were analyzed using Spitters' reciprocal-yield model to explore inter-specific and intra-specific effects. Regressions of T. natans percent cover, N. odorata percent cover, number of T. natans rosettes, and number of N. odorata leaves against planting density were statistically significant. Inter-specific competition from N. odorata was 2.27 times more effective than intra-specific competition on T. natans percent cover. These analyses indicate that N. odorata exerts more competitive pressure on T. natans than T. natans on N. odorata or either species intra-specifically. However, these analyses also indicate that N. odorata may facilitate T. natans seed production. Understanding competitive interactions between T. natans and other species can help inform management decisions.