(abandoned since 2018)
In 2010, we set-up the Trait-based Experiment (Ebeling et al. 2014) to investigate species interactions and to mechanistically understand biodiversity–ecosystem functioning relationships using specific-species trait information (i.e. plant height, leaf area, rooting depth, root length density, phenology). The Trait-Based Experiment focuses on gradients in species diversity as well as functional diversity. The design uses three different plant species pools. For each pool, species diversity is expressed as a different number of species in different plots. Within the gradient in plant species richness, plots differ in their functional diversity, i.e. the trait space which is covered by the plant species mixtures. In other words, species pools have a gradient from very similar plant traits to species with completely different plant traits.
Our statistical design therefore realized different hierarchical levels of combination: (i) different species richness levels ranging from monocultures to 2-, 3-, 4-, to 8 species mixtures, (ii) three different species pools with different trait combinations focused on spatial resource use (e.g. root characteristics), temporal resource use (e.g. plant phenology), or on both together. Regarding defined plant traits, species within each species pool were divided into four different sectors, whereas species within the same sector are very similar and species from different sectors very dissimilar. Functional diversity is defined as the number of sectors covered by a specific species mixture from high number of sectors as being functionally diverse to single sectors being functionally low diverse. In total, 138 plots (3.5 m x 3.5 m) were set up, and in order to maintain different soil characteristics randomly arranged in three blocks with an equal number of plots in each block. All possible combinations result in 8 monocultures, 16 two species, 12 three-species, 9 four species, and 1 eight-species mixtures per species pool. Experimental plots were mown and weeded to maintain the target composition.