1. Soil nutrient availability and functional traits interact in complex ways during the assembly of tree communities hindering our understanding of the implications that this may have for their phylogenetic and functional diversity.

2. We combined abundance, taxonomic, phylogenetic and functional trait data of 222 tree species distributed along nutrient concentration gradients at twenty-four plots in two tropical forest study sites. We analysed micro and macronutrient concentration in organic and topsoil horizons and tested for: (1) nutrient-based species sorting due to contrasting trait-environment relationships; (2) whether nutrient filtering has consequences for phylogenetic and functional diversity, and functional space size and occupancy; and (3) we mapped trait distributions across the phylogeny of tree species to track the evolutionary signature of nutrient availability.

3. We found that total nitrogen (N), available phosphorus and total potassium in soil accounted for 68% of the variation in tropical tree species community composition, with strong associations with nutrient concentration for 89% of the tree species included in the analysis. This nutrient-based species selection was mediated by interactions between the three soil nutrient concentrations with leaf nitrogen, leaf thickness and wood density. Soil N concentration was positively associated with the functional space at the site level. At a plot level soil N concentration positively correlated with functional evenness and it was negatively associated with the functional space not occupied by any species in the tree community. Despite the phylogenetic conservatism of leaf N across tree lineages even when not considering legumes, many sister-species pairs show contrasting values which match with their habitat preferences thus indicating the evolutionary lability of this trait, particularly within recently diversified clades.

4. Synthesis. Our results demonstrate that soil nutrient-based species selection is a prevalent driver of community assembly in tropical forests, a process mediated by key functional traits within the leaf and wood economics spectrum. Functional space size and its filling increase with soil nutrient concentration, whereas niche vacancy decreases. This selection process has likely influenced tropical tree species diversification patterns via habitat specialization.

Data collected during fieldwork campaigns in French Guiana.

Tree community data: Abundance, taxonomic, phylogenetic and functional trait data of 222 tree species distributed along nutrient concentration gradients at twenty-four plots in two tropical forest study sites in French Guiana.

Soil nutrient concentration data: Micro and macronutrient concentration in organic and topsoil horizons from each study plot.

All the analyses where carried out with R software and the code is therefore provided in R programming language.