BUFFERING OF THE EFFECT OF ACID-RAIN ON DECOMPOSITION OF C-14-LABELED BEECH LEAF LITTER BY SAPROPHAGOUS INVERTEBRATES

The effect of simulated acid rain on the decomposition of C-14-labelled beech leaf litter (4 months old), and the modification of this effect by litter fragmentation by the millipede Glomeris marginata (Villers) and by the burrowing activity of two earthworm species [Lumbricus castaneus (Savigny) and Octolasion lacteum (Orley)], was studied in laboratory experiments over a period of 168 days. The acid rain caused a strong decrease in C mineralization of intact beech leaf litter situated on the surface of the carbonate-rich mineral soil (to 0.43 of control), whereas CO2 production by the systems was increased (up to 1.12 times the control level). In general, the activity of the decomposer macrofauna buffered the effects of the acidity. Litter fragmentation by G. marginata reduced the effect of acid precipitation on litter decomposition by almost 50%. The burrowing activity of L. castaneus and O. lacteum led to contact between the intact leaf litter and the mineral soil, which buffered the effect of the acid precipitation on litter decomposition by 82% and 65%, respectively. The epigeic earthworm species L. castaneus, by feeding on and removing the faecal pellets of G. marginata from the soil surface, almost totally buffered the effect of the acid rain on pellet decomposition. The activity of the endogeic earthworm species O. lacteum in feeding on Glomeris faecal pellets and mixing them with mineral soil also buffered the effect of the acid rain. However, this effect appeared to be restricted to the first 5 weeks. In total, by mixing fragmented litter with mineral soil, O. lacteum stabilized organic matter in the mineral soil horizon. This stabilization effect was assumed to be independent of the simulated acid precipitation. In addition, the activity of O. lacteum compensated for the increased CO2 production induced by the acid rain. An intact soil faunal community is therefore considered to be a key component in the buffering characteristic of beechwood mull soils.