Assessing interactions between environmental factors and aquatic toxicity: Influences of dissolved CO2 and light on Cd toxicity in the aquatic macrophyte Potamogeton crispus

Abstract

The objective of this study was to investigate the combined effects of varying dissolved CO2 concentration (ambient CO2, 3˜17 μmol L−1, elevated CO2, 48˜81 μmol L−1) and light intensity (high light, c. 150 μmol photon m−2 s−1, low light, c. 25 μmol photon m−2 s−1) on the bioaccumulation and phytotoxicity of cadmium (Cd) in a macrophyte Potamogeton crispus, under constant Cd exposure. The data confirmed that 100 μM Cd led to adverse changes in morphology, ultrastructure and biochemistry in P. crispus. The toxic effects depended strongly on CO2 concentration and light intensity: elevated CO2 and high light both increased Cd concentrations in P. crispus, and there was a significant interaction between the two factors. Compared to high light grown plants, the photochemical efficiency and chlorophyll content of low light grown P. crispus were much less affected and the MDA content was lower, when exposed to 100 μM Cd. In addition, an antioxidative response was observed with a significant increase in SOD, POD and GST activities, indicating that low light grown P. crispus are more protected against Cd toxicity. When compared with ambient CO2 concentrations, chlorophyll content, chlorophyll fluorescence, photosynthetic rate and starch content, as well as the activity of SOD and GST, were significantly enhanced in Cd treated P. crispus under elevated CO2. This suggests that elevated CO2 reduced Cd toxicity in P. crispus by increasing photosynthesis and enhancing the antioxidant system. Moreover, the statistical results showed that dissolved CO2 and light had additive effects on Cd toxicity in P. crispus, reflected by the physiological parameters of total chlorophyll content, SOD activity and MDA content, indicating that the combination of high CO2 and low light produced more protection against Cd toxicity than did the factors alone. Based on the results of this study, it appears clear that referring to a specific site in aquatic ecosystem, dissolved CO2 concentration and light availability should be considered when assessing and managing Cd impacts on aquatic plants.