DOI: 10.5061/dryad.1jwstqjqh
title: Data from: Multiple facets of diversity effects on plant productivity: species richness, functional diversity, species identity and intraspecific competition

description: 1. Deciphering the mechanisms that drive variation in biomass production
 across plant communities of contrasting species composition and diversity
 is a main challenge of biodiversity-ecosystem functioning research. Niche
 complementarity and selection effect have been widely investigated to
 address biodiversity-productivity relationships. However, the overlooking
 of the specific role played by key species have limited so far our
 capacity to comprehensively assess the relative importance of other
 potential drivers of biodiversity effects. 2. Here, we conducted a
 grassland diversity-productivity experiment to test how four potential
 facets of biodiversity effects, namely species richness, functional
 diversity, species identity and the relaxation of intraspecific
 competition, account for variations in above and root biomass production.
 3. We grew six plant species in monoculture, as well as in every
 combinations of two, three and six species. Plant density was kept
 constant across the richness gradient but we additionally grew each
 species in half-density monoculture to estimate the strength of
 intraspecific competition for each studied species. We characterized eight
 functional traits, including root traits, related to nutrient and light
 acquisition and computed both the functional dissimilarity and the
 community weighted mean (CWM) of each trait. We further partitioned
 aboveground biodiversity effect into complementarity and selection
 effects. 4. We observed strong positive biodiversity effects on both
 aboveground and root biomass as well as strong positive complementarity
 effect. These arose largely from the presence of a particular species
 (Plantago lanceolata) and from CWM trait values more than from a higher
 functional dissimilarity in plant mixtures. P. lanceolata displayed the
 highest intraspecific competition, which was strongly relaxed in species
 mixtures. By contrast, the presence of Sanguisorba minor negatively
 affected the productivity of plant mixtures, this species suffering more
 from interspecific than intraspecific competition. 5. This study provides
 strong evidences that the search for key species is critical to understand
 the role of species diversity on ecosystem functioning and demonstrates
 the major role that the balance between intraspecific and interspecific
 competition plays in biodiversity-ecosystem functioning relationships.
 Developing more integrative approaches in community and ecosystem ecology
 can offer opportunities to better understand the role that species
 diversity plays on ecosystem functioning.
description: We conducted an experiment at the Center for Functional and
 Evolutionary Ecology, Montpellier, France. We grew six plant species in
 monoculture (6 combinations), as well as in every combinations of two (15
 combinations), three (20 combinations) and six species (1 combination) in
 a greenhouse with three replicate pots for the monoculture, two and three
 species combinations and six replicates for the six species combination.
 Plant species were common European herbaceous species: two grasses
 (<i>Bromus erectus</i> Huds., <i>Dactylis
 glomerata</i> L.), two forbs (<i>Plantago lanceolata</i>
 L., <i>Sanguisorba minor</i> Scop.) and two legumes
 (<i>Lotus corniculatus</i> L., <i>Trifolium
 repens</i> L). After all species had shown first
 signs of flowering, we cut aboveground parts of plants at the base and
 separated the six plant individuals to measure aboveground biomass of each
 individual plant. We evaluated root biomass of each pot. We measured eight
 functional traits: 1) light-saturated leaf photosynthetic rate per area
 (Amax, µmol<sub>CO2 </sub>m<sup>-2
 </sup>s<sup>-1</sup>); 2) maximum height (cm);
 3)Specific leaf area (SLA, m².kg<sup>-1</sup>); 4) Root
 inter-branch distance (RID, cm); 5) Specific root length (SRL,
 m.g<sup>-1</sup>); 6) Root hair length (RHL, cm); 7) specific
 root nitrogen absorption rate (N<sub>abs </sub>µg
 <sup>15</sup>N m<sup>-1</sup>
 h<sup>-1</sup>) and 8) deep root fraction.
 For each trait, we computed both community weighted mean (CWM)
 and functional dissimilarity (Fdis) of each plant mixture.