There is general scientific consensus that biodiversity increases productivity of plant communities. Biodiversity enhances productivity through biotic and abiotic, above- and belowground mechanisms. A way of quantifying biodiversity is measuring the diversity of functional traits of plants in plant communities. However, given the large number of potential functional traits, the identification of traits, which result in high biodiversity effects, is difficult. In the first experiment of thesis, I narrowed down a number of aboveground traits, with aggregated trait gradients in a Principal Component Analysis. The results suggested that biodiversity has an explicit spatial component. Plant communities containing species, which were diverse in their spatial traits, resulted in better biomass production. Additionally, the increases in biomass production were a result of increasing individual density, a spatially explicit feature. In the second experiment, I explored further the explicit spatial component of biodiversity effects by recording plant cover on a very small spatial scale in two years. I found species-poor communities had segregated plant cover of species with little change of cover location between years. In contrast, species-rich communities had intermixed plant cover of species with high change of cover location between years. These cover responses to biodiversity underline the explicit aboveground spatial component of biodiversity effects. In the final experiment of thesis, I used a quantitative genetic approach for identifying further functional aboveground traits responding to a history with biodiversity of their maternal plant. Additionally, I tested the hypothesis whether differing light availability of species-poor and species-rich communities is an important driver of selection in grasslands. The results of this experiment confirmed selection of spatially explicit plant traits in relation do biodiversity and light availability. Together, the results of this thesis suggest, that optimization of space-use, probably in relation with more efficient light interception, is a key mechanism of how biodiversity enhances community productivity. Past research focussed on optimization of space-use mainly in relation with resource partitioning along the vertical axis of plants. The results of this thesis expand on this past research by putting a spotlight on the horizontal arrangement of plant species in relation to biodiversity as an underestimated mechanism of productivity increase.