Flower longevity and duration of pistil receptivity in high mountain plants

Flowers of high mountain plants are generally long-lived to compensate for the low frequency of pollinator visits at higher altitudes. However, nothing is known about floral plasticity when pollinators are absent because of unsuitable weather conditions. We investigated both, actual longevity of naturally pollinated flowers and potential flower longevity, the capacity to prolong corolla life-time and pistil receptivity when pollination is retarded. Seven high mountain plant species from different elevations in the European Alps were tested: Gentianella germanica, Ranunculus alpestris and Saxifraga caesia are restricted to the alpine zone, Cerastium uniflorum, Ranunculus glacialis, Saxifraga bryoides and Saxifraga moschata occur from the higher alpine to the glacier zone.Flower longevity differed greatly among species, according to their taxonomic background and their gender sequence type. Actual flower longevity ranged from a few days (G. germanica, C. uniflorum, R. alpestris) to more than two weeks (saxifrages, R. glacialis). Unpollinated flowers generally increased longevity, but the plasticity of single floral functions was quite different. Stigma receptivity could be maintained longest. Pollen adhesion was enabled during the full stigma life-time. High levels of pollen germination and pollen tube growth were still possible 29 days after anthesis (DAA) in R. glacialis, and 23 DAA in S. bryoides. In the remaining species this ability was gradually lost or, in C. uniflorum, abruptly ended around 10 DAA. The overall pistil receptivity primarily depended on the duration of ovule receptivity, which in most species ended between 16 and 20 DAA. Corolla life-time was significantly prolonged in S. bryoides, S. moschata and G. germanica. In the remainder of species mean corolla longevity did not differ from the actual longevity, and thus any prolongation of female functions over the corolla life-time would not contribute to reproductive success. The maximal potential longevities of individual flowers with fresh corolla and receptive pistils were 21 d in S. moschata followed by S. caesia (19 d), S. bryoides, R. glacialis (18 d) and G. germanica (14 d). R. alpestris (8 d) and C. uniflorum (8 d) exhibited the shortest potential overall flower longevities. Contrary to our expectations, flower longevity did not significantly differ between the alpine and the high-elevation species.