Integrated Responses of Hydrocotyle vulgaris at Different Temperatures and Rhodamine B Stress

Rhodamine B (RhB) release and its residues in the water bring environmental and human health risks. To explore integrated responses of Hydrocotyle vulgaris L. to high concentrations of RhB and different temperatures under RhB stress, we first tested the growth performance of H. vulgaris to different concentrations (5-100 mg/L) of RhB at 25 °C. Plant biomass, root activity, and photosynthetic pigment contents decreased, while those for osmoregulators and antioxidants increased with increasing RhB concentrations. However, the growth performance of H. vulgaris did not change significantly at 20 mg/L RhB exposure. Then we tested H. vulgaris responses under 20 mg/L RhB exposure at varying temperatures. H. vulgaris showed similar responses at 15 °C and 35 °C compared to 25 °C, with a removal efficiency of 97% RhB at 35 °C. Mass spectrometry analysis confirmed that RhB underwent progressive oxidation and was ultimately degraded into small-molecule compounds by H. vulgaris, thereby reducing its overall ecotoxicity. Therefore, while H. vulgaris shows potential for dye remediation under controlled temperatures; its practical application requires further consideration of complex field variables in natural aquatic environments.