Assimilation of Aboveground Litter Carbon Versus Soil Carbon by Collembola and Lumbricidae in Spruce Forest: A Litter Replacement Experiment

In a small-scale field experiment, we estimated the contribution of aboveground litter to the energy budget of different collembolan and earthworm species. In a 50-year-old spruce plantation, the natural spruce litter was replaced by an equivalent amount of maize litter. The natural difference in the isotopic composition of carbon (C) between the spruce and maize allowed us to estimate the proportions of different carbon sources in the tissues of soil animals. The dependence on litter-derived C was least pronounced in Collembola having low δ15N values, indicating the feeding on non-vascular plants. In contrast, collembolans having high δ15N values belonged to the food chains based on fresh plant residuals. These results suggest that different species of litter-dwelling collembolans may regulate substantially different energy channels. Some species of endogeic earthworms (Aporrectodea rosea and A. caliginosa) utilize aboveground plant residues, though soil organic matter and other belowground sources of carbon prevail in the energy budget of their populations.