Nitrogen addition frequency and propagule pressure influence Solidago canadensis invasion into native plant community

Introduction Propagule pressure (i.e., the number of propagules) has long been recognized to play an essential role in plant invasion. But it is not clear whether propagule pressure influences the invasion of exotic plants into native plant communities when different frequencies of nitrogen are added. Method We established an experiment with three plant communities that included native plant communities alone (four grasses, two legumes and two forbs) or native plant communities with one or five invasive plants, Solidago canadensis, under three frequencies of nitrogen addition (no addition or low or high addition with the same amount). Results High propagule pressure significantly enhanced the biomass and relative dominance index of S. canadensis. Moreover, high propagule pressure only decreased the total and aboveground biomass of the legumes. However, the competitive effect between S. canadensis and the native community and biomass of the whole native community varied according to different frequencies. Conclusion Overall, high propagule pressure encouraged invasion by S. canadensis, while alow nitrogen frequency was advantageous for the native community to resist invasion in this experiment. The results provide a scientific basis to manage and control the invasion of S. canadensis.