Effects of polystyrene microplastics on the seed germination of herbaceous ornamental plants

Although microplastic (MP) pollution has become an environmental issue worldwide, most related research has been confined to marine ecosystems. The impacts of MPs on terrestrial ecosystems, and especially on terrestrial plants, are poorly studied. In our study, different particle sizes (2 μm and 80 nm) and different concentrations (0, 10, 50, 100, and 500 mg·L^-1) of polystyrene MPs were selected as the experimental materials, and their effects on three herbaceous ornamental plants, Trifolium repens, Orychophragmus violaceus, and Impatiens balsamina, were investigated. Seed germination tendency, germination rate, and various physiological and biochemical indicators were observed in the treated plants. The germination rates and germination potentials of these plants decreased significantly as the polystyrene MP concentration increased. Root formation, as well as a decrease in root hair density, was observed. The catalase, superoxide dismutase, hydrogen peroxide, proline, soluble protein, and soluble sugar contents all showed overall trends that increased first and then decreased, which conformed to the "Plant-ES" equation. Thus, polystyrene MPs appeared to have significant inhibitory effects on the seed germination processes of herbaceous ornamental plants.