Plant functional groups and phylogenetic regularity control plant community bioelement composition through calcium and magnesium

The identification of drivers of bioelement concentrations in plant communities is crucial for our understanding of ecosystem functioning. In this respect, soil nutrients, plant biodiversity and functional groups are reported to affect the plant community bioelement composition. However, given the predominant focus on species richness and single elements (or stoichiometric ratios) so far, only little is known about the patterns of the whole suite of bioelements at the community level and whether these patterns can be predicted by evolutionary relationships between co‐occurring species (phylogenetic diversity). To explore this knowledge gap, we used a comprehensive dataset of soil nutrients, plant community composition, phylogeny and aboveground tissue bioelement data from experimental sites established in central European semi‐natural grasslands. Plant community bioelement composition was strongly and exponentially related to community calcium and magnesium (bioelements reflecting deep phylogenetic differences). Plant community bioelement composition and stoichiometry were best indicated by functional group composition (graminoids and forbs) and phylogenetic regularity, whereas phylogenetic richness, phylogenetic divergence and species richness were poor predictors. Bioelement‐rich communities were poor in graminoids and rich in forbs, and tended to have evenly distributed phylogenetic distances (high regularity). No confounding effect of soil nutrients was observed. The links between functional group composition, phylogenetic regularity and plant community bioelement composition suggest that functional groups and phylogenetic diversity are mechanistically connected to ecosystem functions, such as primary production, decomposition, biogeochemical cycling or plant–herbivore interactions, through bioelements.