Neighborhood matters: high phylogenetic diversity of experimental plant assemblages improves community performance

Background and Aims: Although the role played by phylogeny in the assembly of plant communities remains as a priority to complete the theory of species coexistence, experimental evidence is lacking. It is still unclear to what extent phylogenetic diversity is a driver or a consequence of species assembly processes. We experimentally explored how phylogenetic diversity can drive the community level responses to drought conditions in annual plant communities. To this end, we manipulated the phylogenetic diversity of the species assemblages and the water availability in a common garden experiment with two treatments: average natural rainfall and drought.MethodsWe recorded plant survival and the numbers of flowering and fruiting plants per species in each assemblage. High phylogenetic diversity favored species coexistence over time with higher plant survival and more flowering and fruiting plants, especially under severe drought.Key Results. Our results demonstrate the existence of niche complementarity and the convergence of water economy strategies as major mechanisms for promoting species coexistence in plant assemblages in semiarid Mediterranean habitats.ConclusionsOur findings point to high phylogenetic diversity among neighboring plants as a plausible feature underpinning the recent “united we stand” framework, which states that diffuse positive interactions may promote mechanisms for the persistence of rare species in the community. We suggest that the large species number in the regional species pool may be the consequence of assembly processes occurring at small spatial scales, because the success of each species in terms of surviving and producing offspring was greater when the phylogenetic diversity was higher. Our study is a step forward to understand how phylogenetic relatedness is connected to the mechanisms determining the maintenance of biodiversity.