Plant-Earthworm Interaction Favors Invasive Alien Plants Over Natives in Cd-Contaminated Environments

Plant-earthworm interaction confers fitness advantages to the plants, including growth promotion, nutrient uptake, tolerance, and resistance to heavy metal (HM) contamination. Plant dominance and plant-soil nutrient cycle processes of plant invasion in contaminated environments can be mediated by plant-earthworm interaction. However, little is known about whether different functional groups of invasive plants can gain an advantage in HM-contaminated soils when regulated by plant-earthworm interaction. We conducted an experiment to examine the effects of Cadmium (Cd) (with or without) and earthworms (with or without) on the growth of both native and invasive species of legume, grass, and forb functional groups. We found that Cd reduced the biomass of native species and changed the root mass fraction and root-shoot ratio, while earthworms increased the aboveground mass of invasive species. When contaminated with Cd, earthworms increased the aboveground mass of invasive nonlegumes (grasses and forbs) while reducing the biomass loss of invasive legumes. In turn, invasive plants had a positive effect on earthworm mass. The mutually beneficial relationship between earthworms and invasive species in Cd-contaminated environments can enhance the competitive edge of invasive species over natives. This may facilitate invasive species spread, potentially risking Cd contamination and food chain transmission, threatening ecosystems biodiversity, environmental health, and human health. Thus, earthworm management may be an important measure to control the spread of invasive species in Cd-contaminated areas, particularly invasive nonlegumes.