Rising temperature impacts the trace metal uptake and toxicity in aquatic plants - A case study of Ni and Co in Elodea canadensis Michx.

The global warming and environmental pollution are two crucial contemporary concerns. As both are strongly connected with urbanisation and anthropogenic impact on the environment, they often affect the ecosystem simultaneously. Aquatic habitats are particularly susceptible to thermal and chemical pollution. Temperature influences nearly all physical and chemical features of water bodies and trace metals are known for their toxicity to aquatic organisms. However, effects of multiple stressors, cumulative effects as well as response and possible adaptations of organisms are still open questions. Thus, the aim of this study was to characterize the combined effect of temperature and two trace metals (Co and Ni) on the metal bioaccumulation and viability of a model aquatic macrophyte Elodea canadensis Michx. We exposed shoots of E. canadensis to three temperatures and four metal concentrations (together and separately) applied at environmentally relevant levels. Shoot growth and metal concentration in plants were measured after 120 h. Moreover, after 24, 72 and 120 h the changes in leaf cell morphology and viability were analysed. The results showed that metal accumulation was dose-dependent and was not affected by temperature. The growth of plants was not affected by temperature nor metals. On the other hand, the exposure to Co and Ni and the elevated temperature negatively affected cell viability of E. canadensis leaves which manifested by increased permeability of plasma membranes and visible necroses. The greatest damaged leaf areas were determined after 120 h in the highest concentration of both metals and the highest temperature which indicates synergistic impact of trace metals and temperature on performance of macrohydrophytes. The observed phenomena suggest that global warming and/or thermal pollution may have implications for the performance of aquatic macrophytes in chemically polluted waters, their ability to spread and colonize polluted habitats and their suitability in phytoremediation.