Fortpflanzung bei Saxifraga oppositifolia und S. biflora unter alpinen Bedingungen – Fremdbestäubung als genetische Versicherung?

Abstract

Plant populations in alpine or arctic tundra habitats face harsh environmental conditions to which they have adapted their life history traits such as growth form and mating system. Based on in situ pollination experiments with Saxifraga oppositifolia and S. biflora, I illustrate that even closely related species show specific characteristics in their reproductive strategies which are indicative of the predominant selective factors of the respective microhabitats. The early flowering S. oppositifolia is facultatively outcrossing, thus maintaining high levels of intrapopulation genetic variation. Saxifraga biflora grows in habitats with later snow melt and exhibits mixed mating. These differing mating systems can be related to the types and abundances of pollinators present during the respective flowering times. Despite the prevalent opinion that selfing becomes more important with increasing elevation, S. oppositifolia reveals no effect of elevation on its mating system. Accordingly, increasing elevation does not alter the degree of genetic variation within populations. Under experimentally increased ambient temperature, plants of S. oppositifolia tend to reduce their reproductive effort, possibly as a consequence of increased competition. Nevertheless, based on the investigations on the reproductive ecology of the studied Saxifraga species and their pioneer characteristics, I assume that they will be able to colonize new habitats, should they become outcompeted by invading species from lower elevations because of the ongoing global change. It remains open, however, whether there will be a shift in dominance among these Saxifraga taxa.