Sedum hispanicum L., a pioneer species in the gypsum outcrops (Bologna province)

In order to evaluate the colonization ability of Sedum hispanicum L., we analyzed the nursery effect of moss mat and the level of genetic diversity in some population growing on gypsum outcrops. The study area was the SCI IT4050001 Gessi Bolognesi e Calanchi dell’Abbadessa where the species is found within the Habitat "6110* Rupicolous calcareous or basophilic grasslands of the Alysso-Sedion albi”. Sampling design consisted in 20 plots (0.5 x 0.5 m) subdivided by an internal grid of 0.05 x 0.05 m subplots randomly placed within the patches of the Habitat. Samplings were carried out once a week from March to June 2013. For every plot the total moss and S. hispanicum cover was assessed. In 10 subplots randomly selected, for each S. hispanicum individual the crown was recorded by measuring the maximum and the minimum diameter. Reproductive phenophase, according to the BBCH scale (Hack et al. 1992; Meier 1997), was also considered. Results showed that at plot level there is only a slight positive correlation between S. hispanicum and bryophyte cover. At subplot level the number of individuals increases when bryophyte cover increases, although the individuals growing on mosses are less developed than in other substrates. The phenological stage is slightly more advanced when the species grows in particular on Pleurochaete squarrosa. The level and distribution of genetic diversity, as estimated by ISSR markers, are typical of species with mixed mating system. In the populations of S. hispanicum analyzed, sexual reproduction leads to novel genotypes, while clonal regeneration supports the establishment of offspring in the extreme environments where the species grows.