The effect of earthworms (Lumbricus rubellus) and simulated tillage on soil organic carbon in a long-term microcosm experiment

•Respiration of microcosms with liter repeatedly added was measured for 2.4 years.•Litter was added on soil surface, mixed or incorporated by earthworms.•Mixing has the lowest respiration at the beginning and the highest at the end.•Earthworm had higher respiration than mixing at the beginning and lower at the end.

In a long-term (2.4 years) laboratory experiment, we studied carbon (C) loss from microcosms in which intact litter was placed on the soil surface with or without earthworms (Lumbricus rubellus) or was fragmented and mechanically mixed into the soil to simulate the tillage. Two soil and leaf litter combinations common in post-mining sites near Sokolov (Czech Republic) were used: clay with alder (Alnus glutinosa) and sand with willow (Salix caprea).During the first 20 weeks, respiration was highest with surface litter with earthworms, lowest with mechanical mixing, and intermediate with surface litter minus earthworms. From week 20–80, respiration did not differ among the treatments. From week 80–126, respiration was highest when fragmented litter was mechanically mixed into soil. These results applied to both combinations of soil and litter types. At week 126, C stock was highest with surface-applied litter minus earthworms but most of the litter remained on the soil surface. In the mineral soil, the active C pool was significantly lower with surface-applied litter minus earthworms than in the other treatments. Based on microbial biomass and ergosterol content, microcosms with surface-applied litter minus earthworms were dominated by fungi while those with earthworms or litter that was mechanically mixed into soil were dominated by bacteria. Overall, the results indicate that C sequestration in soil is greater when litter is mixed into the soil by earthworms than by mechanical mixing.