Effects of modified Pb-, Zn-, and Cd- availability on the microbial communities and on the degradation of isoproturon in a heavy metal contaminated soil M. Suhadolc a, * , R. Schroll b , A. Gattinger b , M. Schloter b , J.C. Munch b , D. Lestan a a Biotechnical Faculty, Center for Soil and Environmental Science, University of Ljubljana, Jamnikarjeva 101, Ljubljana 1000, Slovenia b GSF-National Research Center for Environment and Health, Institute of Soil Ecology, Ingolsta ¨dter Landstr.1, Neuherberg 85764, Germany Received 23 April 2003; received in revised form 23 April 2004; accepted 15 May 2004 Abstract The effects of modified heavy metal (HM) availability on the microbial community structure and on the microbe-mediated degradation of herbicide isoproturon (IPU) were evaluated in soil with a long-term HM contamination. The fate of 14 C-ring labelled IPU was investigated for over 60 days under controlled microcosm conditions. Phosphate mineral apatite and a water solution of Pb, Zn, and Cd salts were previously homogeneously mixed into the soil material to reduce and to increase the proportion of bioavailable HM, respectively. The availability of Pb, Zn, and Cd was determined by HM fractionation and plant uptake 110 days after the addition of amendments, shortly before IPU addition. Apatite treatment reduced the availability of HM, but did not affect the microbial biomass and the microbial community structure on the genotype level (total soil DNA-RAPD). However, it changed the microbial community structure on the phenotype level, based on the composition of phospholipid fatty acids (PLFA) at the end of the degradation experiment. The degradation of IPU did not change. In contrast to apatite treatment, HM supplementation increased the bioavailability of Pb, Zn and Cd, which resulted in biomass reduction and changes of microbial community structure on the genotypic (total soil DNA-RAPD) and phenotypic (PLFA) level. Increased bioavailability of HM also significantly reduced the rate of IPU degradation and mineralisation. The total mineralisation over a period of 60 days decreased from 12 to 5% of initial 14 C. Increased HM bioavailability did not influence the degradation pathways and kinetics of IPU. q 2004 Elsevier Ltd. All rights reserved. Keywords: Heavy metals; Bioavailability; Microbial structure and function; Genotypic and phenotypic diversity; Degradation of isoproturon 1. Introduction HM soil contamination has become a serious problem in areas of intense industry and agriculture. In Europe, though the extent of affected areas has not been accurately determined, the polluted agricultural lands likely encompass several million hectares (Flathman and Lanza, 1998). The European Union Council directive (EEC, 1986) limits values for concentrations of HM in arable soils to 3 mg kg K1 for Cd, 140 mg kg K1 for Cu, 75 mg kg K1 for Ni, 300 mg kg K1 for Pb, 300 mg kg K1 for Zn, and 1.5 mg kg K1 for Hg. The tendency to use low to medium level HM polluted sites for agricultural production has raised concern about the impact on public health and soil quality. When considering soil quality, an important question must be addressed concerning the relationship between the structure and function (e.g. degradation of pesticides) of microbial communities affected by HM. An increasing body of evidence suggests that HM have a strong influence on the structure of bacterial and fungal communities (Frostega ˚rd et al., 1993, 1996; Sandaa et al., 1999; Kelly et al., 1999; Kozdroj and van Elsas, 2001), although mainly bacteria are able to develop tolerances against HM contamination (Olson and Thornton, 1982; Arnebrant et al., 1987; Diaz-Ravina and Ba ˚a ˚th, 1996; Kelly et al., 1999). It has already been suggested that by affecting the structure of microbial communities, HM might have significant effects 0038-0717/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2004.05.015 Soil Biology & Biochemistry 36 (2004) 1943–1954 www.elsevier.com/locate/soilbio * Corresponding author. Tel.: C386-14-23-11-61; fax: C386-14-23- 10-88. E-mail address: metka.suhadolc@bf.uni-lj.si (M. Suhadolc).