Abstract: Alien plant invasions threaten native biodiversity, disrupt ecosystem functions, and can cause large economic damage. Phenotypic plasticity is considered a key mechanism facilitating plant invasions. Plastic responses can occur not only within a generation but also be transmitted to subsequent generations. However, little is known about how combined plasticity within and between generations affects the growth performance of clonal invaders and their native congeners under drought conditions, and whether clonal invaders benefit more from such plasticity. The parental generation of the clonal invader Wedelia trilobata and its native congener Wedelia chinensis were exposed to drought or control conditions. After ten weeks, rooted offspring ramets from the parental generation were obtained and subsequently exposed to either drought or control conditions. Parental drought significantly enhanced offspring drought resistance in both species. However, the expression of combined plasticity in morphological traits differed significantly between the clonal invader and its native congener. The clonal invader exhibited greater plasticity in specific leaf area and root surface area, while the native congener showed stronger plasticity in root to shoot ratio. Furthermore, combined plasticity significantly increased the total and shoot biomass in the clonal invader’s offspring, a pattern not observed in the native congener. These results indicate that when offspring environments are predictable, combined plasticity can improve offspring drought adaptation in both species, but the clonal invader benefits more. Given the projected increase in drought frequency under climate change, combined plasticity may enhance the competitive advantage of invasive plants, facilitating their establishment and spread in introduced ranges.

Key words: plant invasions, transgenerational effects, epigenetic variation, clonal growth, drought stress, phenotypic plasticity