High invader density alone drives invasive plant dominance, but its impacts on native community biomass and diversity depend on nutrients and microplastics

While high invader density is known to increase the likelihood of invasion success, the consequences of this increased invader density for the diversity and productivity of native plant communities under these interacting stressors remain insufficiently explored.

We conducted a factorial mesocosm experiment using four invasive aquatic macrophytes and five native plant communities to assess the individual and interactive effects of invader density (one or two individuals), nutrient enrichment (enriched or unenriched), and microplastic pollution (presence or absence) on invasion success, as well as on native community biomass and diversity. High invader density substantially increased both the absolute and relative biomass of invasive plants (+75.9% and +32.1%, respectively), and this effect was consistent across nutrient and microplastic treatments.