Stable Isotope Analysis of Centipedes and Soil

Centipede specimens, litter and soil material were dried at 60°C for 24 h. For measuring stable isotope ratios whole centipede specimens were used whenever possible; large animals exceeding the limits of the analysis system were homogenized with a mortar and pestle and an aliquot was used for measuring stable isotope values. Replicates from different sites were analyzed for each species whenever possible. Before measurement litter and soil material was dried and ground with a ball mill (Retsch Mixer Mill MM200, Haan, Germany). Stable isotope ratios, carbon and nitrogen concentrations of animals and of litter and soil material were determined using a coupled system of an elemental analyzer (NA 1500, Carlo Erba, Milan, Italy) and a mass spectrometer (MAT 251, Finnigan, Bremen, Germany) [38 ]. Isotopic values were expressed using the δ notation with δX (‰) = (Rsample−R_standard) / R_standard x 1000, with X representing the target isotope (¹⁵N or ¹³C) and R the ratio of the heavy to the light isotope (¹³C/¹²C and ¹⁵N/¹⁴N, respectively). Nitrogen in atmospheric air and Vienna PD Belemnite served as standard for ¹⁵N and ¹³C, respectively, and acetanilide for internal calibration. Stable isotope values of animals are given as difference to the values of leaf litter sampled from the study sites, i.e. by calculating Δ¹³C and Δ¹⁵N values [39 ].