Comparative germination ecology of two endemic Rhaponticum species (Asteraceae) in different climatic zones of the Ligurian and Maritime Alps (Piedmont, Italy)

Comparative studies of seed germination of closely related taxa can help increase our understanding of the ecological limitations of cold-adapted plants and forecast how they might respond to global warming. No studies exist on the relationship between thermoclimatic belts that classify mountain life zones according to bioclimatic criteria and the germination strategy of alpine plants. The aim of this study was to assess this relationship using two closely related species growing in different thermotypes and to test whether their germination responses were related to the climate at natural sites. Fresh Rhaponticum bicknellii and R. scariosum seeds were cold stratified for 0, 30, 60 and 90 days and tested for germination at 10, 15 and 20 °C. At the same time, seed burial experiments were run in the field and in the plant nursery. A GLM analysis showed that the length of cold stratification affected significantly only the germination of R. bicknellii seeds, while increasing temperatures prompted germination in both species. We found that R. bicknellii adopts a drought-avoiding germination strategy, while R. scariosum germination is favoured by warm temperatures. Our findings support the general view that alpine plants do not share common germination requirements and that any conclusions should be interpreted from a biogeographical and bioclimatic perspective. Therefore, seed germination and seedling establishment of endemic alpine species can also be predicted by looking at the bioclimate of the species’ range.