The allelopathic algicides sanguinarine and berberine reduced the dominance of Microcystis in competition with Chlorella

Abstract

Gramine, sanguinarine and berberine are potential algicides that can significantly inhibit the growth of cyanobacteria. Their effects on other phytoplankton have to be considered, because other phytoplankton species and cyanobacteria usually co-exist. In this study, we have established the relationships between phytoplankton biomasses and their marker pigments. Afterwards, we have assessed the allelopathic effects of three algicides (gramine, sanguinarine and berberine) on the mono-cultured and mixed-cultured cyanobacteria Microcystis and green algae Chlorella. Our results showed that zeaxanthine and lutein can be used to determine the cell densities of Microcystis and Chlorella in the mixed cultures, respectively. Our study also demonstrated that the inhibitory effects of these three allelopathic algicides on the growths of both Microcystis and Chlorella were sanguinarine > gramine > berberine. The concentrations for 50% of the maximal effect (EC50) of sanguinarine against Microcystis and Chlorella were 0.065 and 0.09 mg L−1, respectively; the EC50 values of gramine against Microcystis and Chlorella were 1.687 and 0.870 mg L−1, respectively; and the EC50 values of berberine against Microcystis and Chlorella were 1.969 and 2.397, respectively. The inhibitory effect of allelopathic algicides on the multiple phytoplankton species in mixed cultures was significantly greater than that in monocultures. In mixed cultures without allelopathic addition or in cultures with gramine (0.5–3 mg L−1), the dominant species was Microcystis. However, Chlorella became the dominant species when the concentration of sanguinarine was 0.1 mg L−1 or that of berberine was greater than 0.5 mg L−1. Both species of phytoplankton died completely when sanguinarine levels were greater than 0.1 mg L−1. Our results suggested that the allelopathic algicides sanguinarine and berberine reduced the dominance of Microcystis in competition with Chlorella.