Growth, photosynthesis and respiratory response to copper in lemna minor: a potential use of duckweed in biomonitoring

Aquatic macrophytes are known to accumulate various heavy metals in their biomass. This accumulation is often accompanied by physiological changes which can be used in biomonitoring for aquatic pollution. In this study, the impact of copper [Cu] on the growth of the duckweed Lemna minor, followed by its removal, was studied with 0.1-1.0 mg/L of Cu in a quarter Coic and Lesaint solution at pH=6.1. In order to verify duckweed tolerance to Cu, photosynthesis was measured at the maximal concentration which caused no effect on the plant growth. The results showed that copper inhibited Lemna growth at concentrations >/= 0.3 mg/L. At 0.2 mg/L, the final biomass was approximately four times greater than the initial biomass. Analysis of metal concentration in water showed that Lemna minor was responsible for the removal of 26% of Cu from the solution. In the presence of Cu, respiration was reduced, while photosynthesis increased considerably. Net photosynthesis approximately increased three times compared to the control. Copper was responsible for 130-290% increase in the photosynthetic activities. These results suggested that Lemna minor could be a good tool for the evaluation of copper pollution in biomonitoring programs

Growth response of the duckweed Lemna minor to heavy metal pollution

To assess the tolerance and effect of heavy metals pollution on the duckweed L. minor, the aquatic plants were exposed to different concentrations of copper [Cu], nickel [Ni], cadmium [Cd] and zinc [Zn] in a quarter Coic and Lessaint solution at pH = 6.1 [ +/- 0.1] and under a daily regime of 16 h light [101 micro mol/m[2] s[1]]. Copper at 0.2 mg/L and nickel at 0.5 mg/L promoted the growth of Lemna fronds. At higher concentrations, Cu and Ni inhibited the growth of duckweed; the EC[50] [concentration causing 50% inhibition] were 0.47 mg/L for Cu and 1.29 mg/L for Ni. Cadmium and zinc decreased by 50% the growth of fronds when the medium contained respectively 0.64 and 5.64 mg/L [EC[50]]. Duckweed tolerated Cu, Ni, Cd and Zn at concentrations of 0.4, 3.0, 0.4 and 15.0 mg/L respectively without showing any visible signs of toxicity [chlorosis, frond disconnection and necrosis]. On the basis of visible symptoms and the EC[50] values, the toxicity of the metals on L. minor was in decreasing order of damage: Cu > Cd > Ni > Zn. It was concluded that the duckweed L. minor is very sensitive to copper and cadmium pollution