The relationship between plant functional traits and soil variables is useful for understanding plant community composition and circumscribing plant functional groups to highlight their adaptations to environmental conditions. The principal aim of this study was to explain assembly patterns of coastal vegetation using functional traits along a short edaphic gradient. The work was carried out on the pioneer zone in the coastal lowland vegetation (foredune) in southern Brazil. We selected 40 functional traits related to the morphology and anatomy of leaves, stems and roots for 60 species recorded in 25 vegetation plots positioned along three transects from the shoreline to slacks. In each plot, floristic and soil data were collected, and functional traits measured. We analysed the relationships between species functional traits and soil factors through RLQ and fourth-corner analyses. Salinity and organic matter content were the most significant edaphic factors in the differentiation of foredune vegetation, while the most significant traits to explain plant adaptations to coastal environments were plant height, sclerenchyma, spongy parenchyma and reserves of inulin in the root. Two functional groups of plants were circumscribed: a conservative group formed by trees and shrubs dominated the Woody Community, with low values of SLA (specific leaf area), thick cuticles, high frequencies of phenolic compounds and crystals, woody stems and great plant heights, which tended to invest in permanent aerial organs; and a more heterogeneous group of herbaceous plants (found in Beach Community, Non-floodable, and Wet Communities) with acquisitive characteristics (high SLA values) or conservative strategy (rhizome and xylopodium). Finally, our results suggested that root and stem functional traits, which are infrequently taken into consideration, were useful to differentiate subtropical coastal plants and, in general, to study plant adaptations to environmental conditions in depth
