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 Coïc 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.

Keywords
quatic pollution; Bioindicator; Lemna minor ; Physiological modifications; Growth; Photosynthesis