Yield and yield stability in mixtures of productive grassland species: Does species number or functional group composition matter?

Abstract

In productive agricultural grasslands the relative importance of species identity, species richness and functional group composition for production and yield stability is not clear. We, therefore, tested diversity effects in mixtures of five productive species common in temperate agricultural grasslands in a greenhouse study: Trifolium repens (legume), Lolium perenne, Dactylis glomerata (grasses) and Plantago lanceolata, Taraxacum officinale agg. (forbs). Diversity levels were (i) monoculture; (ii) all possible three‐species mixtures; and (iii) five‐species mixture. Biomass production increased with greater species richness, an effect that was interpreted as a functional response to a higher proportion of legumes in the mixtures. Species identity and functional composition influenced yield and yield stability in different ways. Larger contents of the legume in mixtures increased yield but decreased yield stability while grasses showed the opposite effect in mixtures. The biomass production of forbs was mostly small in mixtures and yield stability decreased with increasing presence of forbs. In productive agricultural grassland, functional group composition, especially the presence of legumes and grasses, seems to be more important for productivity and yield stability than diversity.