Fig. 1.

a Photograph of the field site of the Jena Experiment taken in 2007 showing the main experimental plots (20 × 20 m) varying in plant species richness (1, 2, 4, 8, 16, and 60) and plant functional group richness (one, two, three, and four). The field site is located on the floodplain of the Saale river at the northern edge of Jena (Thuringia, Germany; background). Photograph by A. Weigelt. b Photograph of one exemplary earthworm plot (2 × 4 m) showing the subplots for earthworm density manipulations (1 × 1 m; earthworm and earthworm reduction), and the four octet devices used for the earthworm extraction by electro-shocking. Photograph by N. Eisenhauer. c Photograph of one earthworm subplot showing the planting pattern for phytometer plants (Lolium perenne and Centaurea jacea; five individuals per species and subplot), the removed shoot material of the resident plant community within a radius of 10 cm around the phytometer individuals to reduce aboveground plant competition. Black arrows indicate a distance of 10 cm. Photograph by N. Eisenhauer. d Photograph of the phytometer plants (L. perenne, 1–5; C. jacea, α-ε) of one exemplary earthworm subplot in late April 2008. Photograph by N. Eisenhauer