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.

The effects of human disturbance on the stability of alpine meadow communities, their diversity–stability relationship, and the underlying mechanisms are still not fully understood. Here, we performed a 12-year-long (2007–2018) two-factor (2 × 3) controlled experiment on Kobresia humilis on the Tibetan Plateau. The manipulations included three clipping levels (no clipping, NC; moderate clipping, MC; heavy clipping, HC) and two fertilization levels (no fertilization, NF; fertilization, F). Our results revealed that the two clipping manipulations significantly increased the temporal stability of alpine meadow communities, whose significant increase was more pronounced under the MC than HC treatment. Moreover, asynchrony effects, portfolio effects, and facilitation interactions were all present in the communities under the six types of experimental treatment combinations. Additionally, a selection effect was detected in the compound communities, demonstrating characteristics that are common to different mechanisms. There were no significant differences in the effects of these mechanisms on community temporal stability between the NC–NF and MC–NF interactive communities. The portfolio effects predominated when clipping intensity was moderate under both fertilization and non-fertilization conditions. By contrast, in the compound communities, the selection effect predominated. In summary, we conclude that in meadow communities that undergo clipping and fertilization disturbances, facilitation interactions and weak interactions make a greater contribution toward maintaining their temporal stability.