How do climate change and trace metals affect macrohydrophytes?
UWr biologists have investigated how global warming and trace metal pollution affect the viability of macrohydrophytes, or aquatic plants. The results of the experiment, whose main protagonist is the Canadian waterweed, were published in Science of the Total Environment. This is another recent publication by University of Wrocław scientists in this prestigious journal.
Intensive urbanisation and the development of industry and agriculture are contributing to two key and very topical problems for humanity – climate change and chemical pollution of the environment. Among other things, global warming is significantly affecting aquatic ecosystems, which have seen a marked increase in water temperature in recent decades, affecting almost all physical and chemical characteristics of water bodies and plant metabolic processes.
Increased temperature, by disrupting natural biogeochemical cycles, can contribute, among other things, to an increase in the content of trace metals in aquatic ecosystems, which are among the most environmentally troublesome pollutants. They are highly persistent in the environment, are non-biodegradable, readily bioaccumulate in organisms and reduce the natural capacity of the environment to regenerate.
Elevated temperature disrupts the proper functioning of aquatic plants and interferes with their growth and development. At the cellular level, it adversely affects the composition of membrane lipids and the balance between the production and elimination of reactive oxygen species (ROS), leading to protein degradation, increased permeability of cell membranes and abnormal ion exchange. This results in a decrease in cell viability and ultimately leads to cell death.
Similar effects associated with increased ROS production, such as disruption of cell membrane integrity and function, changes in chloroplast structure and consequent chlorosis and leaf necrosis, can be exerted by high concentrations of trace metals.
Given that plants are exposed to multiple stressors simultaneously in the modern world, research analysing the simultaneous effects of these stressors is needed to better understand their response. Accordingly, biologists from the University of Wrocław conducted a laboratory experiment in which submerged aquatic plants of Canadian waterweed (Elodea canadensis Michx.) were exposed to elevated temperature and two trace metals (cobalt and nickel), which were added to the experimental system together and separately.
In the study, they tested the hypothesis that exposure of the sea urchin to trace metals and elevated (suboptimal for this species) temperature would result in increased metabolic rates and thus increased bioaccumulation of metals in tissues and increased toxicity.
A very important assumption of the research was to conduct the experiment under conditions similar to those to which the plants are exposed in the natural environment, i.e. corresponding to the expected increase in water temperature and metal concentrations recorded in polluted ecosystems. This will allow the results obtained to be related to the actual pressures to which aquatic plants are subjected in natural habitats. On this basis, the effect of temperature on metal accumulation in plants was investigated using atomic absorption methods and on cell viability using light microscopy.
It was shown that elevated temperature did not increase the bioaccumulation of trace metals in the shoots of Canadian waterweed, but contributed to a decrease in its cell viability. In the case of both elevated temperature and high concentrations of the two metals tested, increased permeability of cell membranes and necrosis occupying a smaller or larger leaf area were observed, with both factors acting simultaneously causing more severe damage than the individual factors acting separately. Moreover, the observed deleterious effects increased in the mixture of metals and with the length of exposure to the adverse factors.
The results of the experiment were published in the high-scoring journal Science of the Total Environment. The article is the result of a collaboration between three researchers from the Faculty of Biological Sciences at the University of Wrocław: dr hab. Ludmiła Polechońska and dr hab. Agnieszka Klink, who are primarily concerned with the chemical ecology of aquatic plants, and dr hab. Katarzyna Sokołowska, prof. UWr, who is a plant anatomist. The results of the study direct attention to the negative impact of global warming and trace metal pollution on the viability of macrophytes and, consequently, the competitiveness of species and the biodiversity of communities in this group of plants. The demonstrated synergistic effects of elevated temperature and metals should be taken into account in environmental chemical contamination risk assessment and remediation and protection measures.
Photographs:
1. Canadian waterweed Elodea canadensis during the experiment (photo: L. Polechońska)
2.Biometric measurements of the Canadian waterweed shoots (photo: L. Polechońska).
3. Microscopic photographs of the leaves of Canadian waterweed.
Left side: In control plants, untreated with elevated temperatures and metals, only single, small necroses are visible on the leaf surface. The cells of the leaf epidermis and mesophyll have numerous, round chloroplasts, and the cell membranes prevent the diffusion of the fluorescent dye propidium iodide from the cell wall into the cytoplasm. Therefore, in the leaves of control plants, the fluorescent signal from propidium iodide is only visible in the cell wall.
Right side: In plants exposed to elevated temperatures and solutions of the metals tested, numerous necroses appear on the leaf surface. Part of the epidermal and mesophyll cells die off (solid arrowheads), chloroplasts degrade and the increased permeability of the cell membranes allows propidium iodide to diffuse into the cytoplasm resulting in staining of the nuclei (empty arrowheads). (photo: K. Sokołowska)
4. Canadian waterweed lily Elodea canadensis in its natural environment (photo: L. Polechońska)
Date of publication: 22.01.2025
Added by: E.K.
