Plant Invasiveness Studies Based On Congener Comparison

Why some species can successfully invade while others can not is a central issue in both invasion biology and dispersal ecology. Comparative approaches are useful in solving this problem.But lots of them have not take phylogeny into account when making comparisons between plants that are inherently different. In contrast, congeneric species are expected to show similar characteristics because of shared evolutionary history. This is especially true of congeners that share the same distribution range. An established invasive congener has been usually presumed to overcome barriers that limited the performance of a native in the same range.Plants of the genus Alternanthera in China are appropriate materials to make comparison studies. Four species of the genus Alternanthera have been found in China:the notorious invasive species alligator weed (A. philoxeroides), the less invasive species A. pungens, the non-invasive alien species A. bettzickiana, and the native species A. sessilis. A comparison study of the four congeneric species has been conducted in this research to better understand the invasion mechanisms of plants of Alternanthera.The main results are as follows:1)The biomass production of alligator weed was higher than that of A.pungens and A. sessilis under conditions with high availability of water and nutrients, but not in conditions of low water availability. This suggested that the invasiveness of alligator weed might be influenced by environmental factors. A. pungens had relatively high biomass production under conditions with low availability of water.2) The SLA and phenotypic plasticity of alligator weed were slightly greater than that of its congeners. Thus SLA and phenotypic plasticity might be useful indexes for predicting the invasiveness of alien species under multiple environmental factors.3)Analysis of population genetic structure with AFLP markers revealed that both A. philoxeroides and A. bettzickiana possess very low genetic diversity, while A. pungens and A. sessilis showing higher genetic variation among populations, suggesting that there was no necessary connection between genetic diversity and invasiveness. Meanwhile, A. pungens and A. bettzickiana showed discriminate intraspecific genetic differentiations.The results of this study will enhance our understanding of the invasion mechanisms of A. philoxeroides and improve the predictive power for invasiveness.