Belowground complementarity effects in a grassland biodiversity experiment are related to deep-rooting species

1. Belowground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects. 2. We determined species-specific root standing biomass over depth using molecular techniques (real time-qPCR) in a large grassland biodiversity experiment (1-8 plant species mixtures), in two years. Species-specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were lin...