Effect of eutrophication on cyanobacteria inhibition by Alternanthera philoxeroides

Abstract

The inhibition of harmful algal growth by alligator weed depends on its nutritional status. Aqueous extracts of Alternanthera philoxeroides exhibited the strongest inhibition of the algae in oligotrophic conditions, moderate inhibition in mesotrophic conditions, and the lowest inhibition in eutrophic conditions. The phytotoxic effect of the culture filtrate decreased gradually in the order: oligotrophication, eutrophication, and mesotrophication. Co-culture in different nutrient conditions showed that algal inhibition by living A. philoxeroides plants occurred in the order: eutrophication > oligotrophication > mesotrophication. It was also confirmed that nutrient status affected the relationship between allelochemical concentration and algal inhibition. Only in mesotrophic conditions did the allelochemical concentration correlate positively with algal suppression. Furthermore, a sawtooth effect was detected among the eutrophication index, algal growth stage, and algal inhibition rate, as well as the allelochemical concentration, algal growth stage, and algal inhibition rate. The forecast equation showed that A. philoxeroides exhibited the greatest inhibition of harmful algae during the lag phase in co-culture, with a 25 mg mL–1 concentration of allelochemicals and mesotrophic conditions (inhibition rate = 85.59%). Key words: Microcosm, Alternanthera philoxeroides (Mart.) Griseb, water bloom algae, eutrophication, allelopathic potential.