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Elevated CO2 Reduces Cadmium Toxicity in a Freshwater Macrophyte

Paper Reviewed
Huang, W., Han, S., Zhou, Q., Li, W. and Xing, W. 2019. Assessing interactions between environmental factors and aquatic toxicity: Influences of dissolved CO2 and light on Cd toxicity in the aquatic macrophyte Potamogeton crispus. Aquatic Toxicology 212: 247-258.

Writing as background for their study, authors Huang et al. (2019) note that the effects of elevated CO2 on the growth and development of terrestrial plants growing in heavy metal-contaminated soils has been extensively studied (see, for example, the several reviews we have posted on this topic in our website's Subject Index under the heading Heavy Metal Toxicity). However, they add that few are such studies focusing on freshwater plants. Thus, it was their objective to examine the impacts of elevated CO2 and cadmium (Cd) toxicity on Potamogeton crispus, a submerged freshwater macrophyte commonly found in lakes, ponds, river and streams.

Their experiment was conducted in a laboratory in a full factorial design of two CO2 concentrations (ambient or elevated to approximately 1000 ppm)), two Cd toxicity levels (no Cd added or 100 µM added) and two light levels (low or high light intensity). After six days of exposure under these various treatment conditions, Huang et al. conducted a number of measurements on the plants to determine their photosynthetic and antioxidative responses. And what did their experiment reveal?

According to the authors, Cd exposure led to "adverse changes in plant morphology, ultrastructure and biochemistry of P. crispus ... confirmed by leaf morphology, ultrastructure of chloroplast, chlorophyll fluorescence parameters, lipid peroxidation and antioxidant enzyme activity." Such negative responses induced leaf chlorosis, a color browning which is readily apparent by visual inspection. As shown in Figure 1, Cd toxicity-induced leaf chlorosis occurred regardless of light treatment. However, its negative impacts were significantly reduced under elevated CO2. This occurred because elevated CO2 improved the photosynthetic efficiency of P. crispus, which enhanced its antioxidant capacity. Consequently, the researchers write that elevated CO2 "alleviate[d] the deleterious properties of Cd," enhancing "the ability of P. crispus plants to tolerate Cd stress." And that is great news for the future growth and development of this freshwater macrophyte.

Figure 1. Photographs of representative P. crispus plants grown for six days at ambient CO2 (AC), ambient CO2 and 100 µM Cd (AC+Cd), or elevated CO2 and 100 µM Cd (EC+Cd), under either high light (HL) or low light (LL) conditions. Adapted from Huang et al. (2019).

Posted 11 November 2019