Timing of Sexual Reproduction and Reproductive Success in the High‐Mountain Plant Saxifraga bryoides L.

Abstract

SAXIFRAGA BRYOIDES L. is one of the plant species reaching the upper limits of distribution for flowering plants in the European Alps. Because of its abundance in the subnival and nival zones, we expected S. BRYOIDES to reproduce efficiently in the highly stochastic climate at higher altitudes. Investigations were carried out at two subnival sites (2650 m and 2880 m a.s.l.) in the Austrian Alps. We studied flowering phenology, dynamics of seed development, and reproductive success in the climatically different years from 2001 - 2004. For a nival plant species, S. BRYOIDES showed a particularly long prefloration period (6 - 9 weeks). From onset of anthesis until seed maturity took an individual flower another 6 - 7 weeks and all individuals at a site 9 - 10 weeks. The length of the prefloration period and seed histogenesis was temperature-dependent, whereas seed maturation seemed to be endogenously controlled. Only in the exceptionally long and warm growing season of 2003 did all fruits mature at a site. In the other years, the onset of winter conditions halted development in many fruits before maturity. The seed/ovule ratio of mature fruits was around 0.7 in all years. The relative reproductive success (RRS) ranged from zero to 0.7, depending on the site and year. In conclusion, S. BRYOIDES needs an unexpectedly long time to undergo reproductive development. Though fruit maturation is uncertain, the high S/O ratio of single intact fruits results in at least a small seed crop in most years. This seems to be sufficient to assure the spread and maintenance of S. BRYOIDES at higher altitudes. As a seed-risk strategist (Molau,1993), S. BRYOIDES would clearly benefit from a prolonged growing season, which might occur more often if climate warming continues.

Dynamics of flower development and vegetative shoot growth in the high mountain plant Saxifraga bryoides L.

“…This staggered flowering minimizes the probability of selfing by geitonogamy (pollination within the same individual; Dafni, 1992). As anthesis proceeds quite uniformly within a flowering cohort (starting with the male phase, and, after anthers have been shed, continuing with the female phase; Ladinig and Wagner, 2007) selfing is largely excluded by distinct dichogamy in this self-compatible species (Ladinig et al, unpublished).…”

“…Macroclimate, and thus the general growing conditions, are about the same for both subnival locations (see Ladinig and Wagner, 2007;Larl and Wagner, 2006). Site climates differed only in the date of snowmelt, the length of the growing season and the temperatures during the growing season (Tables 1 and 2, Fig.…”

“…The flowers are pentacyclic and consist of 5 sepals, 5 petals, 10 stamens and 2 carpels. The flowers are distinctly protandrous, most of them do not unfold the stigma before all anthers are shed (Ladinig and Wagner, 2007).…”

“…Saxifraga bryoides L., a common species in the subnival and the nival belt of the European Alps (Kaplan, 1995), also starts to bloom more than 6 weeks after snowmelt (Ladinig and Wagner, 2007). It is still unclear when and under what conditions floral development is initiated.…”

“…Following on from our earlier study of seed development and reproductive success in S. bryoides (Ladinig and Wagner, 2007), here we investigate the timing of flower and shoot development at three subnival sites with growing seasons of different lengths. The following questions were addressed: (1) when is floral development initiated?…”