Photosynthetic and antioxidant responses of Ankistrodesmus flexuosus and Curvastrum pantanale to environmentally relevant copper concentrations

Since high concentrations of copper (Cu) are known to negatively affect algae, we investigated the effect of environmentally relevant concentrations of Cu on the metabolism and photosynthesis of microalgae. We investigated the photosynthesis and antioxidant responses of two green microalgae, Ankistrodesmus flexuosus and Curvastrum pantanale, to free Cu (1.7 nM-589.0 nM Cu2+), which included environmentally significant values (1.7 nM-21.4 nM Cu2+). The microalgae had similar growth rates at low Cu2+, but C. pantanale had higher growth rates at 7.4 and 21.4 nM Cu2+, and a higher Chl a/b ratio at 1.7-21.4 nM Cu2+. The F-v/F-o of A. flexuosus was not altered by Cu, whereas its relative maximum electron transport rate (rETR(m)) began to decrease at 7.4 nM Cu2+. The F-v/F-o and rETR(m) of C. pantanale increased at 21.4 nM Cu2+. The non-photochemical quenching (NPQ) that was actively dissipated [Y(NPQ)] in A. flexuosus increased with Cu increase, whereas at 589.0 nM Cu2+, the NPQ of C. pantanale decreased and its passive energy dissipation [Y(NO)] increased. C. pantanale had higher photosynthesis at 1.7-21.4 nM Cu2+. Superoxide dismutase (SOD) activity increased in both microalgae at high Cu concentrations, at 21.4 nM Cu2+ for A. flexuosus, and at 589.0 nM Cu2+ for C. pantanale. Thus, environmentally relevant Cu concentrations can favor the survival of tolerant microalgae species, hence shifting the diversity of aquatic biota. (AU)