The influence of aquatic macrophytes on Microcystis aeruginosa growth

Microcystis aeruginosa is a cyanobacterium species that can form harmful algal blooms in freshwater bodies worldwide. The use of aquatic macrophytes to control nuisance algae by allelopathic inhibition will be environmentally friendly and promising. The effects of 8 species of aquatic macrophytes on the growth of M. aeruginosa were investigated, and total phenolics and tannin contents in the macrophytes were determined to reveal the nature of algal inhibition. Artificial addition of 0.1-1% autoclaved leaves and 1% extract from fresh leaves of Iris wilsonii significantly inhibited the growth of M. aeruginosa after 19 days incubation while no significant change was found in the presence of fresh I. wilsonii leaves and 0.1% or 0.5% fresh leaf extracts. Comparative algal inhibition assay showed that all examined tissues of tested macrophytes could significantly inhibit M. aeruginosa whilst the leaves of Nymphaea tetragona, Typha orientalis, Nelumbo nucifera and I. wilsonii presented the most powerful algal inhibition by 75-82% after 19 days, and the leaves of N. tetragona and N. nucifera had higher anti-algal activity than their petioles. Correlation analysis demonstrated that cell density of M. aeruginosa exposed to aquatic macrophyte tissues was negatively correlated with total phenolics and tannin levels in macrophytes, and aquatic macrophytes should have other allelochemicals besides phenolic compounds involved in algal inhibition. Findings suggest that aquatic macrophytes offer the potential for low-effort and sustainable management of freshwaters so as to reduce excessive algal growth. (C) 2012 Elsevier B.V. All rights reserved.