Elevated nitrogen deposition and co-evolutionary history shape competition between an invasive plant and its competitors during range expansion

During the range expansion of invasive plants, competitors shared different co-evolutionary history with invasive plants, as well as population differentiation, would have different effects on the response of invaders to global change factors such as increased nitrogen deposition. Disregard the community responses and potential adaptations of invaders during the range expansion might bring misleading answers. To address these challenges, we conducted a greenhouse experiment to explore the synergistic effects between population differentiation during range expansion and competitors on the invasion of Galinsoga quadriradiata in response to increased nitrogen deposition. Competitors (new or old that shared short or long co-evolutionary history with the invader, respectively) were set to compete with the invasive central and edge populations under different nitrogen addition treatments. Galinsoga quadriradiata from the central population (i.e., with longer residence time since invasion) showed significantly higher total mass, reproduction, interspecific competitiveness when compared to the individuals from the edge population, and the magnitude of response to nitrogen addition treatments was larger in the central population when planted in isolation (single-culture). Nitrogen addition promoted growth and reproductive performance of G. quadriradiata in single-culture, in the presence of competitors this effect was weakened. The old competitors acted more effectively than new competitors in inhibiting the invader performance, mainly for the central population. Our results indicate that population differentiation on growth and competitiveness occurred during the range expansion of G. quadriradiata, with the central population displaying higher invasiveness than the edge population. The co-evolutionary history between invasive species and its competitors has been suggested to be probably not in favor of invasive plants, especially for central populations. Our results highlight the synergistic and non-additive role of population differentiation and shared co-evolution history between invasive species and its competitors in the range expansion of invaders in the context of global change factors.