Study On The Inhibitory Effect Of Two Emerged Plants On Microcystis Aeruginosa

The frequent outbreak of algal blooms is a world-wide problem and has shown an increase in frequency and geographical distribution in recent decades. Large scales of algal blooms degrade water quality, damage the water ecological system, and pose serious threats to aquatic organisms and even human health. Microcystis aeruginosa is one of the representatives of bloom-forming microalgae which occurs in freshwaters. The utilization of allelopathic effect of macrophyte and its extracts in algae control is a relatively cost-effective and environmental-friendly approach. Many researches have proved that aquatic macrophytes have the ability to control algal growth through allelopathic effects, besides competing with harmful algae in light and nutrient.Srirpus validus Vahl and Sagittaria trifolia Linn are two common emergent macrophytes and widely spread in most parts of China. Works have reported that these two plants can absorb nitrogen and phosphorus in eutrophic water and show good effect in water purification. In the present research, the culture water of S. validus and S. trifolia, the rhizome aqueous extract of S. validus, and the tuber aqueous extract of S. trifolia, were prepared to investigate their inhibitory effects on the growth of M. aeruginosa. The inhibitory mechanism of S. trifolia tuber aqueous extract on the algae was also studied.The results showed that both S. validus and S. trifolia showed inhibitory effects on the growth of M. aeruginosa. The higher concentration of the treating solution was, the more obvious the inhibition effect was. The highest inhibition rate of the culture water and rhizome aqueous extract of S. validus, and the culture water and tuber aqueous extract of S. trifolia reached25.32%,67.39%,53.54%, and90.99%, respectively, after120h treatment. On the whole, the inhibitory effect of S. trifolia on M. aeruginosa was stronger than that of S. validus, and the inhibitory effect of plant aqueous extract is stronger than that of culture water.To further investigate the potential inhibitory mechanism, several physiological indexes of M. aeruginosa cells were measured when the algae were exposed to concentration50%of the aqueous extract. The results showed that the chlorophyll-a concentration of M. aeruginosa cells decreased from343.14to314.16μg/L in treatment group, and there was an acute increase in MDA level. It reached the maximal value of5.88μmol/g protein at48h, which was2.7times that in the control group. This result testified that the polyunsaturated acids in cell membranes were attacked by oxygen radicals, and the algal cells were subjected to serious oxidative stress. The activities of superoxide dismutase (SOD), peroxidase (POD) and the content of reduced glutathione (GSH) of M. aeruginosa cells initially increased as a response to the oxidative stress posed by S. trifolia tubers aqueous extract. However, the antioxidant defense system finally lost its function because of the oxidative damage caused by the environment stress. According to the studies mentioned above, it was concluded that the oxidative damage of M. aeruginosa induced by S. trifolia tubers aqueous extract might be one of the mechanisms of the inhibition effects.