[Effects of Microplastics on the Growth and Physiology Characteristics of Ceratophyllum demersum and Hydrilla verticillata].

Plastic consumption and waste contribute to microplastic pollution in aquatic environments. This study aims to investigate the effect of microplastics on the growth and physiological characteristics of aquatic plants, providing a valuable reference for understanding the ecological effects of microplastics and scientific basis for water environment protection. The submerged aquatic plants Ceratophyllum demersum and Hydrilla verticillata were selected to study the effect of cultivation methods (single and mixed), microplastic types (polystyrene (PS) and polyethylene terephthalate (PET)) with a particle size of 100 μm, and microplastic concentrations (50 and 100 mg·L-1) on length growth rate, relative growth rate, biomass, chlorophyll content, antioxidant enzyme activities (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), and malondialdehyde (MDA) content. The results showed that a mixture of C. demersum and H. verticillata was more suitable to cope with PS and PET stress. PS significantly altered the chlorophyll content, POD, and CAT activities, while PET significantly increased the SOD activity. PS and PET of 100 mg·L-1 significantly inhibited the growth of C. demersum. The growth rate of plant height decreased by 32.54%-41.04%, the relative growth rate declined by 56.63%-81.40%, and the biomass reduced by 38.41%-52.86%. The contents of chlorophyll a, chlorophyll b, and chlorophyll a+b of the mixed H. verticillata were significantly increased by 14.80%, 19.82%, and 16.17%, respectively, when treated with 100 mg·L-1 PS. PS and PET significantly reduced the MDA content of the mixed species of C. demersum by 28.13%-49.03%, whereas 50 mg·L-1 PS and PET significantly increased the MDA content of the single species of H. verticillata by 47.45% and 27.39%, respectively. With the increase in the PS and PET concentrations, the activities of SOD, POD, and CAT in H. verticillata were enhanced. In contrast, while the SOD activity of C. demersum increased, its POD activity showed a continuous and significant decline, ranging from 23.93% to 42.28%. CAT activities initially increased and subsequently decreased; however, they consistently remained higher than those in the control group, with an observed increase ranging from 32.23% to 95.11%. The high concentrations of PS and PET exerted significant interference on the growth and development of C. demersum. The effects of PS on the growth and physiological characteristics of C. demersum and H. verticillata were evident.