Stress synergy between drought and a common environmental contaminant: studies with the collembolan Folsomia candida

The term global change is used predominantly in connection with the global temperature increase and associated changes in weather patterns over the ne xt century. In a broader sense it also covers other anthropogenic impacts o n the environment such as habitat fragmentation and pollution. The individu al effects of each of these stress types have been extensively studied in t he biota. However, organisms will frequently encounter these stress types i n combination rather than alone and there is little information available o n the effects of stress combinations. Here an examination is made of the interaction between realistic levels of summer drought and a common contaminant of agricultural soil (4-nonylphenol , NP), on a widespread soil invertebrate, the collembolan Folsomia candida. These stress factors were tested individually and in combination using a f ull factorial design. This approach revealed the existence of highly signif icant Bliss type synergistic interaction between the two stress types. Thus , exposure to NP significantly reduced the drought tolerance of this organi sm and, reciprocally, the toxicity of NP (LC50) during realistic summer dro ught was more than doubled in comparison to the value obtained under optima l soil moisture conditions. Furthermore, it is shown that NP has a detrimen tal effect on the physiological mechanisms underlying this animal's drought tolerance, thus providing some explanation for the mechanisms involved in the synergy. It is argued that this type of synergy is unlikely to be confi ned to this particular combination of stresses and thus there is a need to study the interactions between dominant natural stresses and pollution. The most important implication of these results is that some of the effects of global climate changes can be predicted to be most severe in polluted area s.