The more synthetic polymer types pollute the soil, the stronger the growth suppression of invasive alien and native plants

Although most studies on the ecological effects of microplastic pollution focus on a single type of synthetic polymer and a single species, most organisms will be exposed to multiple polymer types simultaneously and the effects may vary among species. To test the effects of polymer diversity on plants, we grew single plants of eight invasive and eight native species in pots with substrate polluted by 0, 1, 3 and 6 types of micro-sized synthetic polymers. We found that the growth suppression by microplastic pollution became stronger with the number of polymer types the plants were exposed to. This tended to be particularly the case for invasive species, whose biomass advantage over natives diminished with the number of polymer types. Our study thus shows that the negative effects of microplastic pollution on plant growth increase with the number of polymer types, and that these effects differ between invasive and native species.