Phylogenetic and functional diversities offer complementary information to disentangle species assembly processes in experimental gypsophilous annual plant assemblages

Phylogenetic and functional diversities are crucial for understanding community assembly. While the effects of environmental variables on these diversities are well-documented, the causal relationships between phylogenetic and functional diversities and assembly mechanisms remain unclear. To investigate this, we conducted a common garden trial, creating a gradient of initial phylogenetic diversity in experimental annual plant assemblages across eleven combinations of four species each. We measured the resulting functional diversities for three key traits (seed mass, specific leaf area, and maximum plant height) and a multi-trait response. Each species combination received two irrigation treatments: average rainfall and one-third of the average (drought). Our findings highlight the significance of neighborhood effects on reproductive success and life cycle completion. Overall, initial phylogenetic and functional diversities offer complementary insights into species assembly processes, with niche complementarity and competitive asymmetry being critical drivers.