Aims  

This study aimed to measure the effect of plant diversity on N uptake in grasslands and to assess the mechanisms contributing to diversity effects.

Methods  

Annual N uptake into above- and belowground organs and soil nitrate pools were measured in the Jena experiment on a floodplain soil with mixtures of 2–16 species and 1–4 functional groups, and monocultures. In mixtures, the deviation of measured data from data expected from monoculture performance was calculated to assess the contribution of complementarity/facilitation and selection.

Results  

N uptake varied from <1 to 45 g N m⁻² yr⁻¹, and was higher in grasslands with than without legumes. On average, N uptake was higher in mixtures (21 ± 1 g N m⁻² yr⁻¹) than monocultures (13 ± 1 g N m⁻² yr⁻¹), and increased with species richness in mixtures. However, compared to N uptake expected from biomass proportions of species in mixtures, N uptake of mixtures was only slightly higher and a significant surplus N uptake was confined to mixtures containing legumes and non-legumes.

Conclusions  

In our study, high N uptake of species rich mixtures was mainly due to dominance of productive species and facilitation by legumes whereas complementarity among non-legumes was of minor relevance.