Relationship between species abundance, traits occurrence and soil variables in a subtropical coastal dune ecosystem

The relationship between functional traits and soil variables is useful to understand community composition and to circumscribe plant functional groups in order to highlight their adaptations to the environmental conditions. This work was carried out on coastal sand dunes of Ilha do Mel, a protected area located in south Brazil. Coastal dune environments are characterized by a complex interaction between abiotic and biotic factors. We selected 40 functional traits related to morphology and anatomy of leaves, stem and root for 60 psammophytes recorded in 25 vegetation plots positioned along three transects from the shoreline to the transition zone to forest. In each plot, floristic and soil data along with functional traits measurements were collected. We analysed the relationship between species functional traits and soil factors through RLQ and fourth-corner analyses. Organic matter content and salinity were the most significant edaphic factors in differentiation of dune vegetation; while the most significant traits to explain plant adaptations to coastal environment were plant height, the presence of sclerenchyma, spongy parenchyma and reserves of starch and inulin in the root. Our analyses identified two functional groups: tree/shrub species characterized by long-lived leaves with low SLA, thick cuticle, high frequency of phenolic compounds and crystals, woody stems and higher plant height; and herbaceous plants with high SLA values, higher growth speed because of C4 photosynthesis, and reserve structures in the soil that allow rapid growth in unfavourable periods. The main axis of differentiation in subtropical coastal dune plants seem to represent the trade-off between conservative and acquisitive strategies. While tree/shrub functional group tends to invest more in permanent aerial organs, such as woody stem and long-lived sclerophyll leaves; herbaceous functional type invest more in subterranean structures that allow the reconstruction of the photosynthesizing organs in the favourable periods from starch or inulin reserves. Finally, our results suggest that functional traits regarding root and stem, which are less frequently taken in consideration, were useful to differentiate subtropical psammophytes and, in general, to study more in deep plant adaptations to environmental conditions.