Fig. 1. Ombrothermic diagram of (A) air temperature at 2 m above the ground (continuous red line) and precipitation (dashed blue line) and (B) soil temperature (continuous red line) and soil moisture (dashed blue line) at 8 cm below the ground in 2021 and January 2022. The blue vertical stripes in June and September indicate the two mowing periods (14-25.06 and 13-24.09). Data source: local climatic station in the Jena Experiment.
Following a gradient in soil characteristics, the experiment was set up in four blocks containing an equal number of plots per plant diversity treatment within each block to avoid any confounding effects of soil heterogeneity. In total, the study site consists of 80 plots (~5.5 m × 6 m) that differ in levels of sown plant species richness (1, 2, 4, 8, 16, 60 species) and plant functional group richness (one to four of the functional group: grasses, small herbs, tall herbs, legumes). Following common management practices in temperate extensively-used grasslands in Central Europe, where the Jena Experiment is located, the experiment was mowed twice. Moreover, the experimental plots were weeded three times during the study period to maintain the plot’s target species composition.

Temporal above- and belowground sampling

We sampled aboveground and belowground biological response variables biweekly (or every three weeks during winter). Even though the measurements’ definitions differ, e.g., plant community height would be better defined as a biological feature, and detritivore feeding activity is an activity rate, each measured response variable is commonly related to an ecological process (Table 1). We also present a simplified description of the sampling methods for each process. Please see the Supplemental Material for an extended version of the methods.