Exploring the functional strategies adopted by coastal plants along an ecological gradient by means of morpho-functional traits

Coastal dunes are characterised by strong interactions between biotic and abiotic factors along a short gradient from the shoreline to the inland region. We carried out an ecological analysis of the vegetation in a protected area of the Italian coast to evaluate the relationships among species abundance; the occurrence of morphoanatomical traits related to leaves, stems and roots; and soil variables. Three transects were established perpendicular to the shoreline with 27 plots distributed in the frontal dunes, back dunes, and temporarily wet dune slacks. The analysis based on community weighted mean values is consistent with the ecological constraints along the shoreline-inland gradient. The front-plots were characterised by the presence of pioneer communities (with succulent leaves as evidenced by the high limb thickness values and the low LDMC values) that are well adapted to the harsh environmental conditions of these habitats. Farther from the sea, the back-plot vegetation was characterised by functional traits (especially high LDMC values) that are consistent with the less-extreme ecological conditions. Last, the slack-plots seemed to be very interesting from a functional point of view. They were dominated by geophytes that had adopted C4 photosynthesis and had amphistomatic leaves and abundant aerenchyma in the roots. The native vs. invasive status, C4 photosynthesis, leaf trichomes and aerenchyma in the roots were significantly correlated with soil humidity, organic matter content and pH. These results demonstrate the usefulness of anatomical traits (especially those of the root system) in understanding the functional strategies adopted by plants. Last, invasive species tended to occupy plots with high levels of soil humidity, and they were not abundant in the habitats with more arid conditions. These data confirmed that alien species are less adapted to the harsh environmental conditions of coastal sand dunes. Increasing the spatial extent of the study area and integrating other functional traits, such as ecophysiological or regenerative characteristics, into the study may allow the development of a more comprehensive functional framework of the invasion process. All this information can be used to develop appropriate management strategies for coastal dune ecosystems