Abstract: Invasions by non-native plant species are thought to be facilitated by factors like escape from specialized natural enemies and increased resource availability. However, the success of invasive plants also depends on interactions with native plants and soil organisms, including nematodes. Plants can experience both beneficial and harmful interactions with nematodes. Yet, research on how nematodes and nutrient levels interact to affect competition between invasive and native plants is lacking. We conducted a multi-species greenhouse experiment involving 10 invasive species and 20 native species to test the separate and combined effects of nutrient levels and nematodes on performance of individual invasive plant species, as well as their competition with native plant communities. High-nutrient conditions significantly enhanced the aboveground biomass (+119.4%), height (+26.9%), reproduction (+21.0%) and proportional aboveground biomass (+21.2%) of invasive plant species. Conversely, competition from native plant communities significantly reduced the mean aboveground biomass, height, and reproduction of the invasive species by 55.3%, 20.3% and 13.5%, respectively. For invasive plants grown without competition, the high-nutrient treatment significantly enhanced total biomass and root diameter, although it decreased the root mass fraction, independent of nematode presence. In addition, in the absence of competition, nematodes increased the specific root length of invasive plants by 3.6% under low-nutrient conditions but reduced it by 10.1% under high-nutrient conditions. These results indicate that nutrient enrichment, competition and biotic interactions with nematodes can all play critical roles in shaping the growth and adaptive strategies of invasive plant species.

Key words: biological invasions, exotic-native competition, global change, nematode-plant interactions, resource allocation