Plant species richness and functional composition drive overyielding in a six‐year grassland experiment

Abstract

Abstract. Plant diversity has been shown to increase community biomass in experimental communities, but the mechanisms resulting in such positive biodiversity effects have remained largely unknown. We used a large-scale six-year biodiversity experiment near Jena, Germany, to examine how aboveground community biomass in grasslands is affected by different components of plant diversity and thereby infer the mechanisms that may underlie positive biodiversity effects. As components of diversity we defined the number of species (1-16), number of functional groups (1-4), presence of functional groups (legumes, tall herbs, small herbs, and grasses) and proportional abundance of functional groups. Using linear models, replacement series on the level of functional groups, and additive partitioning on the level of species, we explored whether the observed biodiversity effects originated from disproportionate effects of single functional groups or species or from positive interactions between them.Aboveground community biomass was positively related to the number of species measured across functional groups as well as to the number of functional groups measured across different levels of species richness. Furthermore, increasing the number of species within functional groups increased aboveground community biomass, indicating that species within functional groups were not redundant with respect to biomass production. A positive relationship between the number of functional groups and aboveground community biomass within a particular level of species richness suggested that complementarity was larger between species belonging to different rather than to the same functional groups. The presence of legumes or tall herbs had a strong positive impact on aboveground community biomass whereas the presence of small herbs or grasses had on average no significant effect. Two-and three-way interactions between functional group presences were weak, suggesting that their main effects were largely additive. Replacement series analyses on the level of functional groups revealed strong transgressive overyielding and relative yields .1, indicating facilitation. On the species level, we found strong complementarity effects that increased over time while selection effects due to disproportionate contributions of particular species decreased over time. We conclude that transgressive overyielding between functional groups and species richness effects within functional groups caused the positive biodiversity effects on aboveground community biomass in our experiment.

An ecological economic assessment of risk-reducing effects of species diversity in managed grasslands

“…Over the last decade, the search to find the underlying mechanisms of complementarity has often focussed on nutrients (mainly nitrogen) (e.g., Balvanera et al, 2006, Di Falco, 2012, Fargione et al, 2007 as well as -although to a lesser extent -on light (Hautier et al, 2009, Spehn et al, 2000 and water use (Caldeira et al, 2001, De Boeck et al, 2006. Also in the Jena Experiment, nitrogen and light use (Bessler et al, 2012, Gubsch et al, 2011, Roscher et al, 2011a have been reported to contribute to the overall complementarity effect (Marquard et al, 2009). The high N uptake in diverse mixtures thus not only led to higher aboveground productivity, but also to higher nitrogen pools with diversity (Oelmann et al 2011).…”

“…Data further suggested that the main driving force behind such facilitative interactions in plots containing legumes was reduced competition for soil nitrate. Consequently, the presence of legumes (as well as tall herbs) had a strong positive effect on annual yield production (Marquard et al, 2009). However, despite clear evidence of facilitation by legumes in many studies, the wide-spread relationship between species diversity and productivity is not dominantly driven by legumes, as convincingly shown by van Ruijven and Berendse (2003) in a biodiversity study without any legume species.…”

“…With increasing biodiversity, the chance to include a high-productive species also increases, resulting in high yields in diverse communities. For the Jena Experiment, it has been shown that the selection effect decreased over time (Marquard et al, 2009), indicating that differences among plant species in resource niches become more and more important (i.e., niche complementarity), while the importance of individual species diminished over time. All three mechanisms contribute to the positive biodiversity-productivity relationships.…”

“…Fridley, 2002, Vogel et al, 2012, and thus may be the better indicator for (controllable) species diversity levels in the respective field or experimental site. In the Jena Experiment, which is base for our empirical analysis, sown and realized plant species richness/diversity are closely related (Marquard et al, 2009). …”

“…Hodgson et al, 2005). Moreover, diverse grassland systems have been found to be more stable in terms of production (Hector et al, 2010, Proulx et al, 2010, Marquard et al, 2009). For instance, higher diversity has been found to reduce the vulnerability of grassland to climatic extreme events such as droughts as well as to pests and diseases (e.g.…”