Incorporation of carbon and nitrogen from leaf litter differing in structural compounds into soil microarthropods of a deciduous forest

• In the first year of decay, litter is of minor importance for soil mite nutrition.
• High concentrations of structural compounds reduce litter C and N incorporation.
• Leaf litter-derived C and N is incorporated simultaneously into soil mites.
• C and N incorporation varied between soil mite species occupying the same trophic level.
• Mycorrhiza little modify the incorporation of litter resources into soil mites.

Detritivorous soil invertebrates process large quantities of leaf litter material. Focusing on decomposer (Oribatida) and predatory mites (Mesostigmata) we investigated the incorporation of resources from leaf litter rich (European beech, Fagus sylvatica) and poor (European ash, Fraxinus excelsior) in structural compounds using stable isotopes. Using litter mixtures we investigated if soil mites preferentially incorporate carbon (C) and nitrogen (N) derived from beech or ash leaf litter. Using the rotated-core method we established treatments with and without mycorrhiza as interactions between mycorrhiza and saprotrophic microorganisms may alter the availability of litter resources to soil invertebrates. Conform to our expectations primary decomposers incorporated more C and N than secondary decomposers or predators, but the contribution to body tissue element concentration was low suggesting that they predominantly rely on other resources than litter from the previous year. Generally, soil mites incorporated more C and N from ash than from beech litter, but this was less pronounced after 10 as compared to after 5 months, presumably due to fast decomposition of ash litter. In contrast to our expectations the use of litter resources by soil mites was little affected by mycorrhiza. Overall, the results underline that, at least during the first year of litter decay, leaf litter resources are of minor importance for soil mite nutrition, and this is particularly true for litter rich in structural compounds such as beech.