Sexual reproduction of the high mountain plant Saxifraga moschata Wulfen at varying lengths of the growing season

Flowering phenology, dynamics of seed development and reproductive success of Saxifraga moschata Wulfen, occurring from the alpine to the nival zone, was investigated in three climatically varying years on early- and late-thawing sites at 2340 m a.s.l. in the Austrian Alps. The growing season was particularly short in 2001, about normal in 2002 and exceptionally long and warm in 2003. S. moschata is a mid-season flowering species, which started to bloom about 1 month after snowmelt. From onset of anthesis until seed maturity an individual flower required 6–7 weeks, and all individuals of a site 9–11 weeks. In 2001, late flowering individuals lost about 40% of the seed crop because of too early snowfalls in autumn. No clear relationship could be found between thermal time and the length of different reproductive phases, which indicates that temperature was not a limiting factor for reproductive development in the growing seasons 2001–2003.

Plants from the earliest-thawing site produced about double the reproductive structures (reproductive shoots per individual, number of flowers per inflorescence, number of ovules per ovary), and had a significantly higher reproductive output (number of fruits and mature seeds per inflorescence) compared with individuals from the late-thawing site. Reproductive success was additionally affected by the seasonal climate and was lowest in the warm and dry summer of 2003. Fruit/flower ratio ranged between 0.6 and 0.8, seed/ovule ratio between 0.4 and 0.5 and relative reproductive success (RRS) between 0.3 and 0.4, depending on the site and year.

Different from our expectations, it took S. moschata relatively long to undergo reproductive development; however, its phenological plasticity and ability to continue seed maturation even under snow are most advantageous for a life at higher altitudes.