Joint effects of allelochemical nonanoic acid, N-phenyl-1-naphtylamine and caffeic acid on the growth of Microcystis aeruginosa

We studied the combined effects of 3-allelochemicals: nonanoic acid (NA); N-phenyl-1-naphtylamine (PNA) and caffeic acid (CA) on the growth of Microcystis aeruginosa in 2-experiments. In experiment I, the combined effects of 12 mixture groups prepared from these 3-test allelochemicals were studied on M. aeruginosa growth. The combined toxicity of mixtures with equal concentration ratio showed synergism and the joint inhibitory effects became weaker with increase in caffeic acid proportion in the mixtures. These results indicated that two major factors to affect the joint effects of allelochemicals were: mixing ratios and the individual activity of allelochemical. In experiment II, the combined effects were determined on the growth of M. aeruginosa for 9-days. The inhibition ratio of all mixtures increased over time and the highest inhibition was on 7 th or 8 th day. The joint toxicity of 3-allelochemicals was time dependent and the 72 h (3 day) exposure tests under estimated the joint inhibitory effects of allelochemicals. The results were helpful to reveal the allelopathy mechanisms at ecologically levels and control cyanobacterial blooms in eutrophic water bodies.