A trait-based integration of competition and abiotic tolerance underlies plant success

Understanding what determines species' ecological success is a central challenge in ecology. Competitive ability and abiotic tolerance are expected to be strong predictors of species success, yet theory predicts a trade-off between them. Since some traits are phylogenetically conserved whereas others are evolutionarily labile, species may have the potential to combine competitive ability with abiotic tolerance. We conducted a garden experiment involving 23 wetland species under two contrasting hydrological regimes and quantified performance measures to assess species responses to competition and abiotic conditions. We also measured structural, physiological, and morphological traits, and related both to species success, quantified as realized niche breadth and local dominance across 19 000 vegetation plots. Niche breadth and local dominance were most strongly associated with competitive effect, and to a lesser extent with abiotic tolerance. The most successful species expressed traits associated with a phylogenetically conservative persistence-stature functional dimension (high LDMC, tall stature, and deep roots) together with traits of evolutionarily labile acquisitive physiology (low δ¹³C, high stomatal conductance, and elevated leaf nitrogen), indicating high gas exchange and sustained carbon acquisition while trading off rapid growth. Our findings show that competitive strength and abiotic tolerance can co-occur, helping explain why certain evolutionary lineages dominate wetlands.