The buffet is open: Alpine soil macro-decomposers feed on a wide range of litter types in a microcosm cafeteria experiment

Alpine semi-natural grasslands were formed by hundreds of years of traditional and extensive land-use resulting in a distinct flora and fauna. Socio-economic changes in the last century led to the abandonment of a large number of alpine pasturelands. Even though litter composition and quality will permanently alter due to shifts in plant species composition, consequences of abandonment and the subsequent shrub encroachment on the feeding activities of decomposers are not well known. We conducted cafeteria feeding experiments in microcosms in a climate chamber with four abundant alpine decomposer species (two earthworms and two millipedes), offering them three representative alpine litter types (dwarf shrub, grass, and forb) as single litters and mixtures. The epi-endogeic earthworm Lumbricus rubellus (Hoffmeister, 1843), dominant in alpine pastureland, had highest mean consumption rates (34.7 +/- 24.7 mg), while Dendrobaena octaedra (Savigny, 1826), a strictly epigeic earthworm, showed considerably lower consumption rates. Millipedes showed similar consumption patterns, with Cylindroiulus fulviceps (Latzel, 1884) being less active than C. meinerti (Verhoeff, 1891). We found several cases where litter mixtures were preferred over single litters, including higher consumption rates of low-quality dwarf shrub litter by D. octaedra and C. meinerti when mixed with high-quality litter. The tested specimens showed a high intra- and interspecific variability as they fed on all offered litter types and qualities, resulting in few specific food preferences and selections. We conclude that alpine soil macro-decomposer such as earthworms and millipedes are generalists feeding on a wide range of litter qualities, allowing them, in theory, to better adapt to the litter resources that become available when pastures are abandoned and reverted to shrubland.