Abstract
BackgroundThe different hypotheses proposed to explain positive species richness–productivity relationships, i.e. selection effect and complementarity effect, imply that plant functional characteristics are at the core of a mechanistic understanding of biodiversity effects.Methodology/Principal FindingsWe used two community-wide measures of plant functional composition, (1) community-weighted means of trait values (CWM) and (2) functional trait diversity based on Rao’s quadratic diversity (FDQ) to predict biomass production and measures of biodiversity effects in experimental grasslands (Jena Experiment) with different species richness (2, 4, 8, 16 and 60) and different functional group number and composition (1 to 4; legumes, grasses, small herbs, tall herbs) four years after establishment. Functional trait composition had a larger predictive power for community biomass and measures of biodiversitity effects (40–82% of explained variation) than species richness per se (<1–13% of explained variation). CWM explained a larger amount of variation in community biomass (80%) and net biodiversity effects (70%) than FDQ (36 and 38% of explained variation respectively). FDQ explained similar proportions of variation in complementarity effects (24%, positive relationship) and selection effects (28%, negative relationship) as CWM (27% of explained variation for both complementarity and selection effects), but for all response variables the combination of CWM and FDQ led to significant model improvement compared to a separate consideration of different components of functional trait composition. Effects of FDQ were mainly attributable to diversity in nutrient acquisition and life-history strategies. The large spectrum of traits contributing to positive effects of CWM on biomass production and net biodiversity effects indicated that effects of dominant species were associated with different trait combinations.Conclusions/SignificanceOur results suggest that the identification of relevant traits and the relative impacts of functional identity of dominant species and functional diversity are essential for a mechanistic understanding of the role of plant diversity for ecosystem processes such as aboveground biomass production.
Highlights
Rapid decline in biodiversity has motivated considerable research directed towards understanding how changes in biodiversity affect ecosystem functioning [1,2]
Mathematical partitioning of net biodiversity effects into complementarity and selection effects as proposed by the ‘‘additive partitioning method’’ [7] has shown that mostly both effects contribute to positive species richness–productivity relationships in experimental grasslands (e.g. [7,8,9,10,11])
In spite of considerable overlap among species assigned to different plant functional groups in the ordination space, the first principal component clearly separated legumes from grasses, while tall herbs and small herbs were more scattered between these functional groups (F3,56 = 38.50, P,0.001; Tukeys HSD test: P,0.001 for comparisons among legumes, grasses and herbs; P = 0.357 for comparison between small herbs and tall herbs)
Summary
Rapid decline in biodiversity has motivated considerable research directed towards understanding how changes in biodiversity affect ecosystem functioning [1,2]. Experimental biodiversity–ecosystem functioning research has demonstrated the importance of biodiversity for a number of ecosystem processes such as plant productivity, but it remains a central challenge to identify the underlying mechanisms [2]. Mathematical partitioning of net biodiversity effects into complementarity and selection effects (the latter similar to sampling effects) as proposed by the ‘‘additive partitioning method’’ [7] has shown that mostly both effects contribute to positive species richness–productivity relationships in experimental grasslands Selection as well as complementarity effects imply that ecosystem properties such as community productivity strongly depend on the functional characteristics of the constituent species. The different hypotheses proposed to explain positive species richness–productivity relationships, i.e. selection effect and complementarity effect, imply that plant functional characteristics are at the core of a mechanistic understanding of biodiversity effects
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