Low pH in simulated acid rain promotes the toxicity of copper on the physiological performance in Sargassum horneri.

In order to investigate the interactive effects of simulated acid rain and copper (Cu) on macroalgae, Sargassum horneri was cultured under pH of 8.2, 5.6, 4.5 and Cu concentrations of 0, 25, 100 µg L-1. Under the medium concentration of Cu, moderate pH mitigated the toxicity of Cu on S. horneri, while the low pH and high Cu concentration reduced the contents of chlorophyll (Chl) a and carotenoids. Furthermore, pH had no interaction with Cu on maximal Chl fluorescence or electron transport efficiency, while effective PSII quantum yield, maximum electron transport rate, and saturating irradiance were obviously affected by pH and Cu, and the interactive effects were significant. Additionally, with the increasing Cu concentration and decreasing pH, nonphotochemical quenching and regulated energy dissipation dropped sharply, while nonregulated energy dissipation increased. Therefore, the high concentration of Cu and low pH had synergistic effects on the photosynthetic performance and growth of S. horneri. [ABSTRACT FROM AUTHOR]