Taxonomic, functional, and phylogenetic diversity of communities hosting Ionopsidium savianum (Brassicaceae) growing on serpentine and limestone substrates

We analysed two different plant communities hosting Ionopsidium savianum (Brassicaceae), a species of EU interest included in the Habitats Directive 92/43/CEE annexes, for which specific studies on the ecology of communities where the species grows are lacking and more in-depth knowledge is needed. We examined two important sites of occurrence of this species in Tuscany with different soil types, namely limestone (Mt. Calvi) and serpentine (Mt. Pelato), to determine the structural and functional profile of the communities hosting this species in such different contexts. At each site, we surveyed the plant communities with I. savianum in ten 1 m2 quadrats to determine information on communities' species composition and total plant cover, as well as taxonomic (species richness, and Shannon H’ index), phylogenetic (phylogenetic diversity, mean nearest taxon distance and mean pairwise distance) and functional diversity (focusing on Rao’s Q, leaf functional traits and adaptive strategies community weighted mean). We took into account site location, soil type, slope aspect and microrelief as plot-level environmental factors. The two communities were highly diverging from multiple points of view. Differences were in species composition, richness and diversity, with Mt. Calvi hosting higher diversity. The indices of phylogenetic diversity were influenced significantly by site and microrelief, allowing the presence of peculiar niches occupied by the fern Asplenium ceterach. From the functional point of view, communities at Mt. Calvi showed a higher functional diversity and a higher specific leaf area. Plant height was influenced by the slope aspect and was higher on north-facing slopes. In terms of Grime’s adaptive strategies, the Mt. Pelato communities resulted to be more stress tolerant than those surveyed at Mt. Calvi. Here, a decrease in stress-tolerant strategy associated with an increase in ruderal strategy was detected in communities on north-facing slopes.