Fatty acid composition and change in Collembola fed differing diets: identification of trophic biomarkers P.M. Chamberlain a,b , I.D. Bull a , H.I.J. Black b , P. Ineson c , R.P. Evershed a, * a Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK b Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, UK c Department of Biology, University of York, PO Box 373, York YO10 5WY, UK Received 5 December 2003; received in revised form 24 November 2004; accepted 27 January 2005 Abstract To assess the potential of fatty acid (FA) compositions to act as biomarkers in the soil food web, two species of Collembola, Folsomia candida and Proisotoma minuta, were switched to four possible diets: Cladosporium cladosporioides (a common soil fungus), Panagrellus redivivus (a bacteria feeding nematode), Zea mays (maize) and Alnus glutinosa (alder). The change in FA content of the Collembola was observed over the following 39 days. The four diets produced significant shifts in the FA compositions of the Collembola, with P. redivivus causing the most extreme changes; Collembola fed P. redivivus gained complex FA compositions similar to those of the nematode diet. Changes in the relative abundances of some FAs were found to follow negative exponential curves, as the components either accumulated in, or were removed from, the FA pool in the Collembola; abundance half-lives varied between 0.5 and 22.4 days, indicating that Collembolan FA compositions changed readily with the input of new exogenous components. The results demonstrate that Collembolan FA compositions are influenced by diet, and that the abundances of FAs such as i15:0, i17:0 and 18:1(n-7) may be used as biomarkers of nematode consumption by Collembola. In contrast, the C 20 polyunsaturated FAs cannot be used as biomarkers for nematode predation as Collembola possess the ability to biosynthesise high abundances of these compounds when not provided by the diet. q 2005 Elsevier Ltd. All rights reserved. Keywords: Diet; Biomarker; Fatty acids; Polyunsaturated; Collembola 1. Introduction The use of fatty acids (FAs) as trophic biomarkers is common in aquatic ecosystems (e.g. Nelson et al., 2001; Auel et al., 2002), but their potential use in soils, for example in soil food web studies, has not been well explored. Amongst soil organisms, the FA compositions of bacteria and fungi have been extensively investigated (e.g. Zelles, 1999; Madan et al., 2002; Baath, 2003), as have the FA compositions of nematodes (e.g. Chitwood and Krusberg, 1981; Tanaka et al., 1996), and there has been limited, fundamental, research into the FAs of enchytraeids (Jacob et al., 1991), slugs and snails (Weinert et al., 1993; Zhu et al., 1994) and earthworms (e.g. Albro et al., 1992; Petersen and Holmstrup, 2000). However, there has been very little study of the FAs of microarthropods such as Collembola (Stransky et al., 1986; Holmstrup et al., 2002; Haubert et al., 2004; Ruess et al., 2004) and mites, which are significant and common components of the soil biological community (Blakely et al., 2002). Fewer investigators still have examined the changes in the FA compositions of soil organisms over time (rare exceptions being Chen et al. (2001) and Haubert et al. (2004)), or the rates of turnover of FAs in such organisms. The analytical challenge of determining the composition of the small quantities of FAs present in soil organisms, such as the microarthropods, has also been a hurdle resulting in the lack of previous work. Fatty acids occur in many forms in organisms. Phospho- lipid fatty acids (PLFAs) are structural components of cell membranes, while neutral lipid fatty acids (NLFAs) in triacylglycerols act as a store of energy and are often the dominant form in which FAs are found in insects (Stanley-Samuelson et al., 1988). Fatty acids may also occur as free components or bound in glycolipids and steryl Soil Biology & Biochemistry 37 (2005) 1608–1624 www.elsevier.com/locate/soilbio 0038-0717/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2005.01.022 * Corresponding author. Tel.: C44 117 9287674; fax: C44 117 9251295. E-mail address: r.p.evershed@bristol.ac.uk (R.P. Evershed).