F. Gugerli, SEXUAL REPRODUCTION IN SAXIFRAGA-OPPOSITIFOLIA L AND SAXIFRAGA-BIFLORA ALL (SAXIFRAGACEAE) IN THE ALPS, International journal of plant sciences, 158(3), 1997, pp. 274-281
Plant life in high alpine or arctic areas is strongly limited by abiot
ic rather than biotic environmental factors. In climate warming, invad
ing plants from lower altitudes may outcompete indigenous alpine speci
es, which might only survive by colonizing new habitats. Because diasp
ores are most effective for long-distance dispersal, colonizing specie
s mostly depend on reproduction by seeds. The breeding systems of Saxi
fraga oppositifolia and Saxifraga biflora were investigated in the fie
ld. Saxifraga oppositifolia was found to be mostly cross-pollinated, a
nd S. bipora showed a mixed mating system. Relative seed set (seed:ovu
le ratio) was higher in S, biflora than in S. oppositifolia. Saxifraga
biflora also showed a higher relative reproductive success (RRS) in n
aturally cross-pollinated plants, because of high fruit set, and in ge
itonogamous selfing compared with S, oppositifolia. Germination percen
tage was lower in S, biflora than in S. oppositifolia, but only a few
seeds germinated in both species. Variation of germinability could not
be attributed to the pollen source of the various pollination treatme
nts. Saxifraga oppositifolia is among the earliest plants to flower in
spring, at a time when low temperatures Limit pollinator activities.
Since pollen transfer is essential in this preferentially outbreeding
species, S. oppositifolia is a typical ''pollen risker'' Late-flowerin
g species such as S, biflora have numerous pollinators at their dispos
ition and usually display a high selfing rate. Early snowfall, however
, can destroy the whole seed crop. In this context, S. biflora resembl
es a ''seed risker.'' Because of a high outcrossing rate, ''pollen ris
kers'' are expected to have a high genetic variability, which is regar
ded as preadaptation to stochasticity in tundra habitats and to climat
e fluctuations. A possible future climate warming will reduce the chan
ces that ''seed riskers'' lose their whole seed yield, which could be
advantageous for colonizing new habitats. This demonstrates the need o
f learning about species-specific reproductive strategies in order to
make predictions on the vulnerability of tundra plants in a changing c
limate.