Effects of water quality characteristics on the algicidal property of Alternanthera philoxeroides (Mart.) Griseb. in an aquatic ecosystem

The algicidal effects of Alternanthera philoxeroides were analyzed based on a combination of a field survey and laboratory tests, as well as testing the effects of heavy metals in aquatic ecosystems. In the field investigation, a phytoplankton assemblage surrounding A. philoxeroides was significantly inhibited. A. philoxeroides also exhibited strong allelopathic potential in the laboratory. In particular, aqueous extracts significantly suppressed Chlorella pyrenoidosa and Microcystis aeruginosa. Thus, it was assumed that functional allelochemicals produced by A. philoxeroides may help it to compete and combat harmful algae. We also discovered that heavy metals (Ni, Pb, Cr, and Cu) found in an aquatic ecosystem reduced the algicidal potential of A. philoxeroides. However, certain elements other than heavy metals, i.e., the inorganic anions F-, S2-, Cl-, and SO42- and the metallic cations K+, Na+, Ca2+, Mg2+, total Fe, Zn2+, and total Mn, could enhance the inhibitory rate of A. philoxeroides. Based on an analyses of these relationship, we found a significant relationship between the rate of the suppression of the tested algae by the A. philoxeroides allelopathy and the concentration of metallic cations in the aquatic habitat, but not the concentration of inorganic anions. (C) 2012 Elsevier Ltd. All rights reserved.