Degradation of metalaxyl-M in contrasting soils is influenced more by differences in physicochemical characteristics than in microbial community composition after re-inoculation of sterilised soils Kate L. Baker a, b, c, * , Samantha Marshall b , Graeme W. Nicol a , Colin D. Campbell c, d , Gilles Nicollier e , Dean Ricketts b , Kenneth Killham a , James I. Prosser a a Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK b Syngenta, Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK c The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK d Department Soil and Environment, Swedish University of Agricultural Sciences, Box 7014, SE-750 07 Uppsala, Sweden e Syngenta Crop Protection AG, 4002 Basel, Switzerland article info Article history: Received 9 October 2009 Received in revised form 6 March 2010 Accepted 12 March 2010 Available online 3 April 2010 Keywords: T-RFLP Fungicide degradation Metalaxyl-M Soil microbial community composition Community swap Sterilisationere-inoculation abstract Rates of degradation of pesticides by soil microorganisms are believed to depend on both microbial community composition and underlying soil physicochemical characteristics. The aim of this study was to determine which of these factors was more important in determining the rate of degradation of the fungicide metalaxyl-M in two soils. Soils exhibiting highly contrasting metalaxyl-M degradation rates were sterilised by gamma-irradiation and inoculated with either non-sterilised soil from the same site or with the soil from the contrasting site. After re-establishment of microbial communities, soils were treated with metalaxyl-M and the degradation rate (measured by 14 C-HPLC), pH and microbial community structure (multiplex terminal-restriction fragment length polymorphism (T-RFLP) analysis of small subunit rRNA gene sequences) were assessed. Community composition was altered by the sterilisation and re-inoculation strategy but degradation in re-inoculated soils was still most rapid in the soil with the original faster degradation rate. This was the case regardless of the source of the soil inoculum, and the rate of degradation in the soil exhibiting the low natural degradation rate remained low when inoculated with the faster-degrading soil. The results suggest that while the slower-degrading soil possessed a degradative capacity, the degradation rate in this soil was significantly reduced by some of its physicochemical char- acteristics, despite introduction of the microbial community of the faster-degrading soil. These results and this experimental strategy provide a basis for the assessment of relative importance of the factors limiting biodegradation and management strategies required to enhance degradation rates. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Microorganisms play a vital role in ecosystem processes and are responsible for decomposition of organic material and cycling of nutrients (Prosser, 2002). The high diversity of soil microbial communities provides the potential for a wide range of processes, but it is difficult to distinguish roles of community composition and soil physicochemical properties in ecosystem functioning. This reduces the ability to predict the influence of environmental change and different management strategies on ecosystem functions, including those contributing to bioremediation. Agricultural pesticides are important globally for increasing crop yields but not all applied pesticide reaches target organisms and the remainder can be a potential hazard until microbial degradation. Hence relatively rapid pesticide degradation in soil is desirable. Degradation rate depends on the presence of relevant microorganisms and of appropriate soil physicochemical proper- ties, including pH (Walker et al., 2001), soil texture (Walker, 1976; Choi et al., 1988), organic matter composition (Xing and Pignatello, 1997), water availability and temperature (Walker, 1978; Choi et al., 1988), and on chemical structure and mode of action of the pesticide. Differences in pesticide degradation rate between soils may therefore result from differences in microbial community composition, but this hypothesis is difficult to test due * Corresponding author at: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK. Tel.: þ44 01224 274489; fax: þ44 01224 272703. E-mail address: k.baker@abdn.ac.uk (K.L. Baker). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2010.03.016 Soil Biology & Biochemistry 42 (2010) 1123e1131