Sediment type and nitrogen deposition affect the relationship between Alternanthera philoxeroides and experimental wetland plant communities.
Wetlands have been demonstrated to be susceptible to invasions. Nutrient availability of wetland sediment is strongly affected by both sediment type and nitrogen deposition. We performed a greenhouse experiment to investigate the main effects and interactions between the presence of Alternanthera philoxeroides, sediment type and nitrogen deposition on biomass and evenness of experimental wetland plant communities. We established two types of plant communities, specifically wetland plant communities without and with A. philoxeroides, in two different sediment types crossed with two nitrogen deposition treatments. Experimental wetland plant communities consisted of four native or naturalised wetland species. Sediment type and nitrogen deposition significantly promoted A. philoxeroides growth. At the community level, the presence of A. philoxeroides decreased the total biomass of wetland plant species and increased community evenness, whereas sediment type significantly decreased evenness. At the species level, the presence of A. philoxeroides significantly decreased total biomass of Iris wilsonii and increased total biomass of Pontederia cordata. However, the interaction between invasion and nitrogen deposition significantly increased total biomass of Butomus umbellatus. These findings suggest that both sediment type and nitrogen deposition promote A. philoxeroides growth and exacerbate A. philoxeroides invasion into wetland plant communities. However, the presence of A. philoxeroides can increase the evenness of the wetland plant communities at a small scale by suppressing dominant species. The findings of the present study provide insights into the management of A. philoxeroides in wetlands.