Vertical stratification and trophic interactions among organisms of a soil decomposer food web – a field experiment using 15N as a tool

• Published in: European journal of soil biology Vol. 38; no. 1; pp. 29 - 34
• Main Authors: Setälä, Heikki, Aarnio, Tuula
• Format: Journal Article
• Language: English
• Published: Paris Elsevier Masson SAS 2002; Editions scientifiques et médicales Elsevier
• Subjects: 15N label; Agronomy. Soil science and plant productions; AZOTE; Biochemistry and biology; Biological and medical sciences; CANADA; Chemical, physicochemical, biochemical and biological properties; FAUNA DEL SUELO; FAUNE DU SOL; FOREST LITTER; FOREST SOILS; Fundamental and applied biological sciences. Psychology; HOJARASCA FORESTAL; HUMUS; ISOTOPE RADIOACTIF; LITIERE FORESTIERE; MICROORGANISME DU SOL; MICROORGANISMOS DEL SUELO; NITROGEN; NITROGENO; NIVEAU TROPHIQUE; NIVELES TROFICOS; PERFIL DEL SUELO; Physics, chemistry, biochemistry and biology of agricultural and forest soils; PODZOL; PODZOLES; PODZOLS; PROFIL DU SOL; PSEUDOTSUGA MENZIESII; RADIOISOTOPES; RADIOISOTOPOS; SOIL FAUNA; SOIL MICROORGANISMS; SOIL PROFILES; Soil science; SOL DE FORET; SUELO FORESTAL; Trophic interactions; TROPHIC LEVELS; Vertical stratification; Zoology (interactions between soil fauna and agricultural or forest soils); Scandinavia; Europe; Finland; Soil fauna; Vertical stratification; 15N label; Trophic interactions; Organic matter; Podzolic soil; Litter; Isotope labelling; Vertical distribution; Decomposer; Forest soil; Pseudotsuga menziesii; Urea; Humus; Food web; Softwood forest tree; Gymnospermae; Coniferales; Spermatophyta; Detritivorous; Nitrogen fertilizer; Field study
• ISSN: 1164-5563
• DOI: 10.1016/S1164-5563(01)01119-0

In this field study, we explored the spatial segregation between the litter- and humus-inhabiting organisms of the detrital food web using 15N-isotope technique. The study was established in 11 × 11 m plots fertilized with 15N-labelled urea. Ten years after urea application, soil samples were taken, both from the litter layer and the combined F+H layer. The samples were analysed for N content and the proportion of 15N in (i) the residual organic matter in the litter and F+H layer (excluding microbes), (ii) microbial biomass, and (iii) various feeding guilds of soil fauna. The basal resource, soil microbes, and the fauna were more enriched with 15N in the F+H layer than in the litter layer. In the litter layer, the 15N enrichment of the expected food source equalled the one of the consumers, whereas in the F+H layer all trophic groups, except microbes and small microbi-detritivores, showed a significantly lower 15N enrichment than their expected food source. The results indicate that large and mobile humus-inhabiting decomposers exploit the overlying litter layer as a feeding site, whereas the feeding of the more sedentary smaller organisms is restricted to the humus layer.