Effects of fluoride on soil fauna mediated litter decomposition.

To evaluate the effect of potentially toxic compounds on soil fauna mediated carbon and other mineral fluxes in poplar litter, a terrestrial micro-ecosystem (MES) was developed, with the isopod Porcellio scaber as a representative soil fauna species. An experiment was conducted, in which MES with isopods were compared to MES without isopods. Potassium fluoride was used as a model compound. The isopods influenced the microbial respiration negatively. No effect was found for the isopods on the nitrogen and phosphorus mineralization. After the first four weeks of the experiment the total respiration of the MES was increased and the phosphate concentration decreased at the highest fluoride concentration. After nine weeks, fluoride decreased ammonium, nitrate and phosphate concentrations in the litter. It is concluded that nitrogen and phosphorus mineralization in the MES are more sensitive to effects of fluoride that microbial respiration. The no observed effect concentrations for net mineralization of ammonium, nitrate and phosphorus were, respectively, 17, 5.3 and 53 micromol fluoride per gram dry weight of litter. Fluoride seems to be toxic for microbial processes at concentrations found in moderately polluted areas.