Impact of genetic diversity of an earthworm on decomposition and ecosystem functioning

Ecosystem functioning is affected positively by increased biodiversity, through complementary functions of multiple species or because high-functioning species are more likely in a species-rich community. Genetic diversity is one level of biodiversity that has been shown to positively affect ecosystem functioning. Whether the genetic diversity of a key decomposer species affects decomposition processes, and ecosystem functioning in general, is still unknown. We compared low and high genetic diversity assemblages of the earthworm Dendrobaena octaedra in two different experiments: using microcosms containing a simple community of other decomposer animals (some nematodes and other microfauna) and using microcosms with a more complex community, including also another earthworm species, diverse microarthropod fauna and enchytraeid worms. We studied the soil decomposition activity through measurements of mineral nitrogen and CO2-production. In addition, the wellbeing of the earthworms was followed by determining their biomass, cocoon production, mortality and gene expression. Very few differences between low and high diversity microcosms were found, often in only one of the years studied. When differences were found, these depended on which genotype was present in the low diversity treatment. Our results suggest it is not genetic diversity per se, but specific genotypes of key decomposer species that can affect ecosystem functioning.