Grassland Diversity Experiment in Jena, Germany

The study was carried out in the Jena Experiment, a large-scale grassland diversity experiment in the floodplain of the Saale River near the city of Jena Thuringia, Germany; 50°57´N, 11°35´E^{39 (link),40 (link)}. In spring 2002, 82 experimental grassland plots of 20 × 20 m were established. Plots are arranged in four blocks to account for changes in soil characteristics with increasing distance from the river, typical for a flood plain. Specifically, soil texture in the upper soil ranges from sandy loam to silty clay with increasing distance from the river. Sand content declines from 40% near the river to 7% at the furthest plot, while silt content increases from 44 to 69%, respectively. The clay content ranges from 16 to 24%, but is not related to distance from the river. The experimental field site of this study was an arable field with mineral fertilizer input to grow wheat and vegetables for about 40 years before the establishment of the Jena grassland experiment. After the last harvest in autumn 2000 the field was ploughed and kept fallow throughout 2001. In preparation for the experiment, and in order to reduce the weed pressure the field was harrowed bimonthly (June, August, October) and treated with Glyphosate (N-(Phosphonomethyl)-glycin, Roundup) in July 2001. In spring 2002 the field was harrowed before the plots were established^{39 (link)}.
Plant communities of different plant species richness (PSR) were established building a gradient from monocultures to 60 plant species mixtures (diversity levels: 1, 2, 4, 8, 16 and 60 species). The plant diversity levels were replicated 16 times, except for the 16 (14 replicates) and 60 (four replicates) plant species mixtures (Fig. 1).Figure 1

The 10-ha site was used as arable land until 2000, and was converted to an experimental grassland in 2002. For this, the area was completely tilled and experimental plots of different plant diversity were sown, separated from each other by paths (left photo: field site in 2002; right photo: field site in 2016). The plant community composition of each plot was randomly selected out of a species pool of 60 grassland species. Each diversity level is replicated 16 times, except for 16 and 60-species mixtures, which have 14 and 4 replicates, respectively. After the plots became established, colonization by above- and belowground fauna began. Left photo by K. Kübler, copyright of right photo by the Jena Experiment.

The species were randomly chosen from a pool of 60 Arrhenatherion grassland plant species and from four functional groups, namely grasses, legumes, small herbs, and tall herbs (Table S1). Functional group classification was based on morphological, phenological, and physiological traits^{39 (link)}. For this study, the PSR levels 1, 4, 16 and 60 were used, resulting in fifty plots. Experimental plots are weeded manually two to three times a year to maintain the target plant community composition. Weeds were mainly species of the species pool that are not sown on the respective plot. The plots are mowed and the mowed plant material is removed twice a year in June and September, but not fertilized, which is typical for extensively managed hay meadows in Central Europe. In 2009 the original plot size was reduced to 105 m^{240 (link)}.