1. Phylogenetic and functional diversities are crucial to understanding community assembly. Although the effects of environmental variables on these diversities are well documented, the causal relationships between phylogenetic and functional diversities with assembly mechanisms remain unclear. 2. To investigate this, we conducted a common garden trial, creating experimental species assemblages with a wide range of initial phylogenetic diversities (ranging from 0.23 to 0.93 PSV values) by manipulating experimental annual plant assemblages. Each experimental assemblage was also described in functional terms using the Rao index for three key traits (seed mass, specific leaf area, and maximum plant height) and a multitrait index. We implemented two irrigation treatments: average rainfall and one-third of average rainfall (drought). We measured the proportion of fruiting plants per species and pot and the seed set per fruit in each experimental assemblage. 3. Synthesis. Our findings highlight the importance of the properties at the species assembly level on reproductive success and life cycle completion of the plants conforming the assembly. Overall, initial phylogenetic and functional diversities offer complementary insights into species assembly processes, with niche complementarity and competitive asymmetry being crucial drivers.

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. Each experimental assemblage was also described in functional terms for three key traits (seed mass, specific leaf area, and maximum plant height) and a multi-trait response. We implemented two irrigation treatments: average rainfall and one-third of the average (drought). We measured the proportion of fruiting plants and seed set per fruit in each experimental assemblage. Our findings highlight the significance of assembly level properties 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.