Adaptations of enchytraeids to single and combined effects of physical and chemical stressors

Abstract

Climate changes are expected to be greatest in the polar and temperate areas, where predictions point to an increase in freeze–thaw events and changes in precipitation, evaporation, and salinity patterns. These events will therefore affect biological activity of the soil compartment that may result in large impacts in ecosystem functioning and dynamics therein. This concern becomes even more important when considering the presence of contaminants due to intense anthropogenic activity, which may lead to synergistic or antagonistic effects and increase or decrease the impact on natural ecosystems. This paper reviews the effect of physical and chemical stressors on enchytraeids, with special emphasis on Enchytraeus albidus because most relevant studies have involved this species. E. albidus is a freeze-tolerant and euryhaline organism and several studies suggest that the absence of salinity may have important (negative) consequences not only for their freeze tolerance ability but also for their reproduction and capacity to deal with the presence of contaminants, such as metals and fungicides. Single and joint effects of constant freezing or freeze–thaw cycles and surfactants, such as 4-nonylphenol, affected negatively E. albidus freeze tolerance by decreasing the levels of cryoprotectants, membrane fluidity and interfering with cellular energy allocation. Because enchytraeids are of ecological significance in many important habitats along the Artic and cold-temperate environments, a reduction in abundance may result in disturbances of the decomposition processes in soils. The knowledge of the biological, physiological, and biochemical limits of enchytraeids to combined effect of physical and chemical stressors are crucial to provide a scientific basis for improving the setting of safety factors when extrapolating from controlled (and optimal) laboratory conditions to natural soil ecosystems. Therefore, there is a need to expand and evolve experiments that more realistically mimic the situation in the field, where interactions between factors are highly relevant. The synergistic or antagonistic interactions identified in the present review may also represent a stepping stone in the evaluation and possible inclusion of natural factors, like cold and salinity, in standardized enchytraeid test guidelines and consequently in risk assessment of chemicals.