EFFECTS OF ACID-RAIN ON LEAF-LITTER DECOMPOSITION IN A BEECH FOREST ON CALCAREOUS SOIL

The effects of simulated acid rain on litter decomposition in a calcareous soil (pH(H2O) 5.8) were studied. Litterbags (45-mu-m and 1 mm mesh size) containing freshly fallen beech leaf litter were exposed to different concentrations of acid in a beech forest on limestone (Gottinger Wald, Germany) for 1 year. Loss of C, the ash content, and CO2-C production were measured at the end of the experiment. Further tests measured the ability of the litter-colonizing microflora to metabolize C-14-labelled beech leaf litter and hyphae. The simulated acid rain strongly reduced CO2-C and (CO2-C)-C-14 production in the litter. This depression in production was very strong when the input of protons was 1.5 times greater than the normal acid deposition, but comparatively low when the input was 32 times greater. Acid deposition may thus cause a very strong accumulation of primary and secondary C compounds in the litter layer of base-rich soils, even with a moderate increase in proton input. The presence of mesofauna significantly reduced the ability of the acid rain to inhibit C mineralization. The ash content in the 1-mm litterbags indicated that this was largely due to transport of base-rich mineral soil into the litter.