In controlled laboratory conditions, the allelopathic effects of emergent macrophyte Acorus calamus L. were studied on the growth of two phytoplankton species: Microcystis aeruginosa Küetzing and Chlorella pyrenoidosa Chick. In co-culture experiment, A. calamus grew normally in the medium but the growth of M. aeruginosa and C. pyrenoidosa was significantly inhibited at initial cell densities by live plants and the inhibitory effect was less on C. pyrenoidosa. Within 10 days, the highest IR value of live A. calamus on M. aeruginosa and C. pyrenoidosa were 97.9% and 82.2%, respectively. The aqueous extracts of A. calamus dry biomass at high concentrations inhibited the growth of both phytoplankton spp. but the growth of M. aeruginosa was revived on 4th day with aqueous extracts concentration of 30 mL.L−1, and growth of C. pyrenoidosa was promoted by the concentrations < 30 mL.L−1. The same amount of aqueous extracts added to M. aeruginosa in single application or in multiple application, caused more inhibition in later. The result suggested that the allelochemicals are degradable and a long-term inhibition might need the continuous addition of compounds from A. calamus. This study showed that A. calamus was strongly inhibitory to phytoplankton and may have great potential in HABs control and prevention.
Allelopathy, Acorus calamus, Chlorella pyrenoidosa, Emergent macrophyte, Growth inhibition, Microcystis aeruginosa
