Plant height and leaf size: Which one is more important in affecting the successful invasion of Solidago canadensis and Conyza canadensis in urban ecosystems?

Abstract

It is still debated whether invasive alien species (IAS) have superior functional traits, especially plant height and leaf size, than co-occurring native plant species (NPS). Meanwhile, as two important indicators affecting the competitiveness for sunlight acquisition, plant height and leaf size, which one is more important in affecting the successful invasion of IAS? Thus, it is vital to assess the differences in the functional trait between IAS and co-occurring NPS and the significance of plant height and leaf size in the successful invasion to further elucidate the mechanisms underlying successful invasion especially with diverse degrees of invasion, especially in urban ecosystems. This study aims to assess the differences in the functional trait between IAS and co-occurring NPS and the significance of plant height and leaf size in the successful invasion of two notorious IAS [i.e., Solidago canadensis L. and Conyza canadensis (L.) Cronq.] with different degrees of invasion (i.e., low and heavy degrees of invasion based on their relative abundance in the invaded habitats) in urban ecosystems by using field sampling experiments. The competitiveness for sunlight acquisition of IAS distinctly increases as the degree of invasion increases. The competitiveness for sunlight acquisition of IAS is evidently higher than that of NPS but contrary to the leaf photosynthetic area. Plant height is more strongly related to the relative abundance of the two IAS than leaf size. The contribution intensity of plant height of the two IAS to their relative abundance is obviously higher than leaf size. Thus, plant height, rather than leaf size, was the most important determinant of the successful invasion of the two IAS, especially under heavy degree of invasion. Thus, the invasiveness of the two IAS is largely contributed by the higher competitiveness for sunlight acquisition rather than the larger leaf photosynthetic area, especially under heavy degree of invasion.