Abstract
Soil food webs are important drivers for key ecological functions in terrestrial systems such as carbon and nutrient cycling. However, soil food web models generally lack quantitative data, mainly due to the shortage in high-throughput methods to describe energy flows. In marine environments, multivariate optimization models (Quantitative Fatty Acid Signature Analysis) and Bayesian approaches (source-tracking algorithm) were established to predict the proportion of predator diets using lipids as tracers. A premise for the application of such models to soil systems is to acquire the fatty acid pattern of a broad range of resources and to reveal potential overlap in their signatures. We present a comprehensive comparison of lipid pattern across widespread taxa of plants (leaves and roots, n = 48), algae (n = 59), fungi (n = 60), and bacteria (n = 62) as basal food web resources. Lipid profiles from microorganisms and algae were assessed from laboratory cultures, whereas plant tissue was derived from an arable field. A lipid library was constructed and multivariate data analyses (hierarchical clustering, nMDS) was used to assess the extent of separation in lipid pattern by species or resource type. The performance of the lipid library was tested by leave-one-prey-out (LOPO) analysis, giving the distinctiveness of the resource (prey) groups. Fungi and plant leaves were correctly assigned based on their lipid pattern with more than 98%, while plant roots and bacteria achieved 88 and 85%, respectively. However, algae were only correctly classified by 60%, pointing to a bias in the herbivore food chain. Fatty acids most important for separation of algae and plant leaves were of the omega 3 type, i.e. 16:3ω3 and 18:3ω3. In plant roots 18:1ω9 was most important, whereas bacteria were distinguished predominantly by methyl-branched fatty acids. Overall, the lipid pattern of major soil food web resources are sufficiently differentiated to allow for qualitative (biomarker) analyses as well as quantitative modelling, yet with precaution in the case of algae.
Highlights
Fatty acids constitute one of the major cell components, forming the membrane as phospholipids and representing the main energy storage as neutral lipids [1]
The total lipid fatty acids (TLFAs) patterns of major basal resources in soil food webs were assessed from a total of 50 different species
The tissue analyses of algae, bacteria, fungi and plants resulted in a combined lipid library comprising 62 bacteria, 60 fungi, 59 algae and 48 plant samples, with the latter separated in 24 leaf tissue and 24 root tissue samples (n = 229; S1 Table)
Summary
Fatty acids constitute one of the major cell components, forming the membrane as phospholipids and representing the main energy storage as neutral lipids [1] Despite this ubiquitous nature, the frequency, diversity and specificity of fatty acids differs among organismic groups. Advanced is the use of fatty acids as trophic biomarkers in marine systems, where ω3 polyunsaturated fatty acids (PUFAs) are almost exclusively synthesised by planktonic algae at the food web base. This allows following the trophic transfer of ω3 PUFAs in many invertebrates and vertebrates of the marine food chain [3, 4, 5]
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