Effects of Conyza canadensis and Lactuca serriola invasion on native plant communities in disturbed habitats

Abstract

Invasive plants can alter native plant communities and soil properties, and their effects may depend not only on their presence but also on their intensity within invaded communities. This study assessed the effects of two invasive species in Asteraceae, Conyza canadensis and Lactuca serriola, on native plant communities in disturbed habitat of South Korea. In ten regions, C. canadensis-invaded, L. serriola-invaded, and uninvaded plots were surveyed. Native plant diversity, the growth performance of the invaders and native plants, and soil chemical properties were measured. Effects were evaluated by comparing invaded and uninvaded plots （invasion status） and by regression against the relative cover of each invader （invasion intensity）. Both invasive species showed higher growth performance than the co-occurring native species, mainly in aboveground traits, whereas the root:shoot ratio did not differ. The two invaders differed in their effects on the native community. In C. canadensis-invaded plots, native plant diversity and growth performance were lower than in uninvaded plots, and the same patterns appeared as C. canadensis relative cover increased. In contrast, native plant diversity and growth performance in L. serriola invaded plots did not differ from those in uninvaded plots, and native plant diversity declined only as L. serriola relative cover increased. Soil chemical properties showed limited associations with invasion. pH was the only property that differed among plot types. C. canadensis relative cover was positively related to soil PO₄³⁻. These results indicate that C. canadensis and L. serriola differ in their impact on native plant communities, with C. canadensis reducing native plant diversity and growth performance and L. serriola exerting weak, intensity-dependent effects.