Influence of fragmentation and bioturbation on the decomposition of 14C-labelled beech leaf litter

The effects of mechanical fragmentation (< 1 mm), the formation of faecal pellets by the millipede Glomeris marginata (Villers) and of bioturbation by two earthworm species [Lumbricus castaneus (Savigny) and Octolasion lacteum (Orley)] on the decomposition of 14C-labelled beech leaf litter (4 month old) and total CO2-C production of soil and fitter was studied over a period of 168 days. Three phases of the effect of faecal pellet formation by G. marginata on C mineralization of the fitter could be distinguished: during the first 14 days C mineralization rates were reduced (up to 0.42 of control); from day 15 to day 77 litter decomposition was increased (up to 1.72 of control); during the last 70 days C mineralization rates were reduced again (up to 0.82 of control). The results are discussed in relation to the effect of the gut passage of the litter on litter components. L. castaneus and O. lacteum fed only on fragmented beech leaf litter. Cumulative C mineralization of intact beech leaf litter was not affected by the presence of either earthworm species. Ingestion of Glomeris faecal pellets and incorporation in the soil by L. castaneus and O. lacteum caused a strong increase in C mineralization of the pellets during the first 14 days. After this initial phase the effect depended on earthworm species. The effect of the litter-dwelling earthworm species L. castaneus was restricted to the initial flush in C mineralization, whereas ingestion and incorporation of faecal pellets in the soil by the soil-dwelling earthworm species O. lacteum caused a significant reduction in cumulative C mineralization (- 39%). Mean C mineralization rates of faecal pellets of G. marginata and of mechanically-fragmented litter ingested by O. lacteum were almost identical to the mean rates of CO2-C production by the systems. The stabilization of organic matter in the mineral soil horizon caused by the burrowing activity of soil-dwelling earthworms is considered to be a key process for the formation of woodland mull soils.