Responses to nutrient addition, shading and clipping in a range expanding invasive plant, Mikania micrantha

Abstract

AbstractInvasive plants often spread in their new range. During range expansion, the population density at the invasion front may be low compared to that at the invasion centre, and this may select for an acquisitive growth strategy, such as rapid growth, stronger responses to nutrient addition, less tolerance to shading and more tolerance to biomass removal. In this study, we tested this idea using 27 populations of an invasive plant, Mikania micrantha, which is spreading on Hainan island of China in the past 20 years. Nutrient addition increased biomass of M. micrantha, and shading and clipping reduced it. Population density, frequency of occurrence and their interaction with nutrient addition, shading or clipping did not influence plant biomass and root to shoot ratio (RSR). For the western populations, both population density and frequency of occurrence were negatively correlated with RSR in the shading treatment. Overall, populations of M. micrantha differed little in growth. The reasons for these results may be that the spread distance and residence time of M. micrantha on Hainan island are too short to drive any evolutionary change, strong interspecific invaders may prevent M. micrantha from acquiring abundant resources when population density and frequency are low, and long distance dispersal of seeds and pollen may potentially mix genes, preventing adaptive evolution. These results indicate that M. micrantha may not evolve to be more invasive during range expansion. Future studies can examine if populations of M. micrantha differ in other aspects, such as seed dispersal ability and competitive ability.