RESPONSE OF PROTOZOAN AND MICROBIAL COMMUNITIES IN VARIOUS CONIFEROUSFOREST SOILS AFTER TRANSFER TO FORESTS WITH DIFFERENT LEVELS OF ATMOSPHERIC-POLLUTION

During recent decades, forest ecosystems have been exposed to high lev els of atmospheric pollution, and it has been argued that this affects the composition and activity of decomposer communities and, subsequen tly, ecosystem functioning. To investigate the effects of atmospheric pollution on protozoa and microflora, a new experimental design was us ed. Undisturbed soil columns, originating from six coniferous forests across Europe and representing different stages of soil acidification, were transferred to two Scots pine forests (Fontainebleau and Wekerom ) with different: levels of N and S deposition (NH4+-N=4.90 and 42.50 kg ha(-1) year(-1); SO4-S=10.90 and 30.40 kg ha(-1) year(-1), respecti vely). The number of protozoa, microbial biomass C and microbial activ ity were estimated in the organic layer (Of) of the transferred soils at the two host sites after 21 months of incubation. The experiment ai med at answering two questions: (1) Do changes in environmental condit ions, studied by transferring soils from one site to another, affect p rotozoa and microbial communities and, if so, (2) how important are ch anges in both N and S deposition in explaining the effects of soil tra nsfer on protozoa and microbial communities? The interaction between p rotozoa and microbial communities was addressed with regard to these c hanges in environmental conditions. No effect of enhanced N or S depos ition on protozoan numbers and microbial biomass C, basal respiration and caloric quotient was revealed. Reciprocal transfer of various soil columns resulted in lower abundance and activity of protozoa and micr obes. This reduction could not be explained by differences in N and S deposition, but by differences in microclimate and adaptation. In some cases, protozoa correlated with pH, CIN ratio, P and S content and le ached mineral N.