EFFECT OF METAL-RICH SLUDGE AMENDMENTS ON THE SOIL MICROBIAL COMMUNITY

The effects of heavy-metal-containing sewage sludge on the soil microb ial community were studied in two agricultural soils of different text ures, which had been contaminated separately with three predominantly single metals (Cu, Zn, and Ni) at two different levels more than 20 ye ars ago. We compared three community-based microbiological measurement s, namely, phospholipid fatty acid (PLFA) analysis to reveal changes i n species composition, the Biolog system to indicate metabolic fingerp rints of microbial communities, and the thymidine incorporation techni que to measure bacterial community tolerance, In the Luddington soil, bacterial community tolerance increased in all metal treatments compar ed to an unpolluted-sludge-treated control soil. Community tolerance t o specific metals increased the most when the same metal was added to the soil; for example, tolerance to Cu increased most in Cu-polluted t reatments, A dose-response effect was also evident, There were also in dications of cotolerance to metals whose concentration had not been el evated by the sludge treatment, The PLFA pattern changed in all metal treatments, but the interpretation,vas complicated by the soil moistur e content, which also affected the results. The Biolog measurements in dicated similar effects of metals and moisture to the PLFA measurement s, but doe to high variation between replicates, no significant differ ences compared to the uncontaminated control were found. In the Lee Va lley soil, significant increases in community tolerance were found for the high levels of Cu and Zn, while the PLFA pattern was significantl y altered for the soils with high levels of Cu, Ni, and Zn. No effects on the Biolog measurements were found in this soil.