Relationships between species richness and biomass production are context dependent in grasslands differing in land-use and seed addition

Abstract

Despite experimental evidence that plant species loss reduces biomass production in grasslands, the strength of biodiversity-ecosystem functioning relationships in semi-natural grasslands is still debated. Land-use and reduced species pools are often suggested to make relationships between biodiversity and productivity less positive or even negative, but concrete evidence is still scarce. We investigated biodiversity-productivity relationships over two years in 150 managed grasslands in Germany. Specifically, we distinguished between relationships of biodiversity and biomass production in grasslands (1) varying in land-use (e.g. of mowing, grazing and/or fertilization), (2) where land-use is experimentally reduced, and (3) where additionally to land-use reductions, species pools are enlarged by seed addition. Among grasslands varying in land-use, we found negative biodiversity-productivity relationships. Land-use reduction weakened these relationships, towards neutral, and sometimes, even positive relationships. Seed addition reduced species pool limitations, but this did not strengthen biodiversity-productivity relationships. Our findings indicate that land-use is an important factor explaining the predominantly negative biodiversity-productivity relationships in managed grasslands. While we did not find that species pool limitations weakened biodiversity-productivity relationships, possibly such effects are only visible in the long-term. Ultimately, advancing insights on biodiversity-ecosystem functioning relationships helps us to understand under which conditions agricultural production may benefit from promoting biodiversity.