Abstract
Alpine pastureland is increasingly abandoned, leading to shrub encroachment and to the accumulation of low-quality litter. Alpine key decomposers such as earthworms were found to feed on both low- and high-quality litter, but little is known how this might affect their life history traits.
To fill this gap of knowledge, we conducted a laboratory experiment with the widespread earthworm species Lumbricus rubellus Hoffmeister, 1843. Hatchlings were provided with either of three aged litter types: grass and forb leaf litter as high-quality food sources and dwarf shrub leaves as low-quality food source. A control group was fed with aged cow dung. Biomass, days until (pre-)maturity, mortality, and reproduction rate were measured regularly to assess the impacts of food quality on earthworm development.
We found pronounced impacts of food source quality on the fitness of L. rubellus. The low-quality litter led to significantly delayed development of up to 53 days, the lowest mean biomass (720 mg after 32 weeks) as well as a 50% drop of produced cocoons compared with the high-quality litter. However, the F2 generation showed the highest hatchling success in the shrub treatment.
We conclude that the increased consumption of low-quality dwarf shrub litter led to negative effects on the development and reproduction of L. rubellus. Overall, this might be the main reason for declining earthworm densities in abandoned Alpine pasture soils, even though the biomass of the second generation was not significantly affected possibly due to a phenotypic variability in reproduction strategy. However, the decrease of such important decomposers and ecosystem engineers can have far reaching consequences for ecosystem processes such as litter accumulation and bioturbation and thus for the stability of Alpine soil ecosystems.