Comparative study of the toxicity responses of Vallisneria natans and Pistia stratiotes to sulfadiazine under different planting methods.

Sulfonamides are receiving increased attention due to their persistence in the environment and potential ecological risks. However, there are currently relatively few studies on the toxicity response of aquatic plants grown under the single and mixed planting methods to sulfadiazine (SD). This study investigated the response of the Vallisneria natans (Lour.) Hara (V. natans) and the Pistia stratiotes L. (P. stratiotes) to SD toxicity under single and mixed planting methods. The findings demonstrated that under the mixed planting method, 0.3 μg/L SD significantly reduced the biomass of V. natans (p < 0.05) while increasing the biomass of P. stratiotes. Under the single planting method, the chlorophyll a content of V. natans and P. stratiotes showed the highest value when exposed to 0.3 μg/L SD. The chlorophyll b content of V. natans and P. stratiotes was higher in the single planting method compared to mixed planting method. In single planting, V. natans exhibited the highest superoxide dismutase (SOD) activity when exposed to high concentrations of SD (3.0 μg/L). However, under the mixed planting method, the SOD activity of V. natans and P. stratiotes reduced at 0.3 μg/L SD. P. stratiotes showed increased malondialdehyde (MDA) and glutathione S-transferase (GST) activities at 3.0 μg/L SD under the single planting method. The comprehensive stress resistance ranking was as follows: single planting (V. natans) > mixed planting (P. stratiotes) > mixed planting (V. natans) > single planting (P. stratiotes). Moreover, exposure to SD downregulated the cell motility metabolic pathway of V. natans and P. stratiotes, particularly under the mixed planting method, to increase the resistance of V. natans and P. stratiotes to SD exposure. Proteobacteria, Actinobacteria and Bacteroidetes were the dominant phyla. This study provides basic data and scientific support for the selection of plants for remediation of higher SD polluted waters using ecological remediation.