TRAIT-BASED FUNCTIONAL CHARACTERIZATION OF PLANT SPECIES AND COMMUNITIES: TRENDS AND ADAPTIONS TO ENVIRONMENT IN ALPINE AND EUROPEAN VEGETATION

Over the last few decades, plant functional traits (morphological, physiological or phenological features, measurable at the individual level, with a direct or indirect effect on whole-plant fitness) have become widely applied to plant ecology; they provide many insights into plant responses to ecological factors, plant resource acquisition and use, plant assemblages and relations within and between communities, from individual to ecosystem scale. A small set of traits that co-vary recurrently among environments has been used to globally identify certain axes of variation, representing the different plant strategies of resources acquisition and use. In particular, plant species have been classified within a three-way strategy model (CSR) proposed by Grime, according to the distinct trait combinations the are selected under conditions of competition (C), abiotic limitation to growth (S) and periodic biomass destruction (R). Variation in plant functioning (captured by variation in trait values) and species distribution depend on variation in environmental factors that can change gradually through space and time identifying gradients which can be determined by different variables such as altitude, latitude, successional stage, resource availability, soil composition, disturbance events (grazing, fire, trampling, floods etc.) and many others. In this study, plant functional traits and Grime’s CSR adaptive plant strategies were applied in order to gain a functional characterization of plant communities of European vegetation at different levels (within and between communities), to highlight functional similarities and/or differences and to identify common patterns and responses to environmental factors. In details, was investigated the role of an additional trait associated to leaf nutrient content (i.e. leaf sulfur content) within the framework of both global spectrum of plant form and function and the CSR plant adaptive strategies, which resulted to be a consistent addition to the acknowledged and commonly used trait set as it was related to other traits identifying the leaf economics spectrum. Plant inter-specific trait variation in response to changes in single ecological factors was also assessed by considering gradients of different Ecological Indicators referring to key environmental drivers, demonstrating that temperature, light conditions and nutrients were associated with clear effects on plant traits, underlining that responses to changes in land use and increased soil nutrient loading could trigger and strengthen responses to climate alteration. CSR plant strategies were also applied to investigate alien species success and adaption to different habitats, showing that alien species occupy the same CSR space and, therefore, the same niches of native species, being also particularly competitive and associated to relatively productive habitats which are highly prone to invasion. Plant functional traits variation was then studied at the community level considering a topographic sequence in in an alpine pasture, in relation to a variety of abiotic and biotic factors, which showed a strong relationship between vegetation, soil properties, topography, and grazing supporting the ability of plant strategy variation to reflect ecological parameters. In alpine environment, multiple plant communities (floristically and ecologically defined, corresponding to Habitat of EU Commmunity interest) were also functionally characterized along a successional gradient at a regional scale, finding a clear pattern of community-level trait variation that reflected the plant economics spectrum (from acquisitive and fast-growing characteristics in pioneer succession stages, to conservative and stress-tolerant features toward the succession climax) demonstrating that plant trait trade-offs can undergo adaptation at the regional scale caused by local environmental conditions. Finally, the functional characterization of classes of European vegetation using their woody diagnostic species was applied to investigate whether traits and CSR strategies reliably indicate plant-environment relations underpinned by the phytosociological classification method, suggesting a solid link between the two main approaches to vegetation description and classification, phytosociology and functional ecology. This Ph.D. project allowed an overall better insight into plant ecology and functioning, starting from the species-level and then moving to the community-level, analysing plant adaptive strategies and trait interactions, and identifying trends and responses to environmental factors.