The seed germination niche limits the distribution of some plant species in calcareous or siliceous alpine bedrocks

Functional plant traits are used in ecology to explain population dynamics in time and space. However, because the germination niche is an essential stage in alpine plant life cycles and is under strong environmental pressure, we hypothesised that inter-specific variability in germination traits might contribute to alpine plant distributions. Germination traits of seven closely related species from calcareous and siliceous habitats were characterised in the laboratory, including base, optimum and ceiling temperatures (T (b), T (o), T (c), respectively), base water-potential (I (b)) and the pH range of the germination phenotype. Species' vegetative traits (specific leaf area, leaf area and leaf dry matter content) were obtained from the TRY-database. Traits and habitat similarities and dissimilarities were assessed. Species were plotted in a multivariate space using two separate principal component analyses: one each for germination and vegetative traits. Species from calcareous habitats showed significantly higher T (b), lower I (b) and lower capacity to germinate under acidic pH than species from siliceous habitats. Moreover, high T (o) and T (c), a narrow temperature range for germination at dispersal, and vegetative traits values were similar across both habitats. Whilst plant traits seem to have adapted to the shared environmental conditions of the two alpine habitats, some germination traits were affected by the habitat differences. In conclusion, species occurrence in two habitats (calcareous, siliceous) appears to be limited by some germination constraints and provide greater differentiation of species habitat preference than that defined by vegetative traits.