PHOSPHOLIPID FATTY-ACID COMPOSITION AND HEAVY-METAL TOLERANCE OF SOILMICROBIAL COMMUNITIES ALONG 2 HEAVY METAL-POLLUTED GRADIENTS IN CONIFEROUS FORESTS

The effects of long-term heavy metal deposition on microbial community structure and the level of bacterial community tolerance were studied along two different gradients in Scandinavian coniferous forest soils , One was near the Harjavalta smelter in Finland, and one was at Ronns kar in Sweden, Phospholipid fatty acid (PLFA) analysis revealed a grad ual change in soil microbial communities along both pollution gradient s, and most of the individual PLFAs changed similarly to metal polluti on at both sites, The relative quantities of the PLFAs br18:0, br17:0, i16:0, and i16:1 increased with increasing heavy metal concentration, while those of 20:4 and 18:2w6, which is a predominant PLFA in many f ungi, decreased, The fungal part of the microbial biomass was found to be more sensitive to heavy metals, This resulted in a decreased funga l/bacterial biomass ratio along the pollution gradient towards the sme lters, The thymidine incorporation technique was used to study the hea vy metal tolerance of the bacteria, The bacterial community at the Har javalta smelter, exposed mainly to Cu deposition, exhibited an increas ed tolerance to Cu but not to Cd, Ni, and Zn, At the Ronnskar smelter the deposition consisting of a mixture of metals increased the bacteri al community tolerance to all tested metals, Both the PLFA pattern and the bacterial community tolerance were affected at lower soil metal c oncentrations than were bacterial counts and bacterial activities, At Harjavalta the increased Cu tolerance of the bacteria and the change i n the PLFA pattern of the microbial community were found at the same s oil Cu concentrations, This indicated that the altered PLFA pattern wa s at least partly due to an altered, more metal-tolerant bacterial com munity, At Ronnskar, where the PLFA data varied more, a correlation be tween bacterial community tolerance and an altered PLFA pattern was fo und up to 10 to 15 km from the smelter, Farther away changes in the PL FA pattern could not be explained by an increased community tolerance to metals.