Influence of chemical agents commonly used for soil fauna investigations on the stable C-isotopic signature of soil animals

The use of stable carbon isotope tracers is an approved method in investigating soil carbon cycle and trophic interactions. Within this methodical study collembolans and nematodes were analysed exemplarily. Prior to stable C-isotopic analysis, the animals have to be killed. A preparation of animal tissues (preservation, bleaching etc.) with different customary agents is often indispensable. Substances usually used contain carbon and hence represent potential carbon sources. Therefore, they could modify the C-isotopic signature of animal tissue. This methodical problem is the key point of the present contribution. The influence of commonly used chemical agents on the C-isotopic signature of collembolans was investigated exemplarily for monoethyleneglycol (MEG), ethanol (EtOH) and lactic acid. Furthermore, effects of TAF, formalin and glycerine on the C-isotopic signature of nematodes were analysed. Overall, most investigated agents modified the δ13C values of animal tissues. Only MEG did not cause any significant alteration in animal C-isotopic signature of both soil fauna groups. In case of collembolans, 96% EtOH also did not change the stable C-isotopic signature significantly. Finally, the use of these agents for soil fauna preparation prior to stable C-isotopic analysis is discussed.