Pollen limitation of Vaccinium myrtillus along an elevational gradient

Plant dependence on pollinator-aided reproduction may decrease with colder
and more unstable climates, for example at higher elevations.
Correspondingly, plant populations may also be more pollen limited in
alpine than in lowlands or under more optimal conditions. However, such
expectations have largely been investigated across species, and rarely
among populations within a species. The findings of such studies may have
implications for predictions of plant sexual reproduction in a changing
climate. We combined a bagging experiment of Vaccinium myrtillus
(bilberry) flowers with a supplemental pollen experiment at three sites
along an elevational gradient at 100, 500 and 900 m a.s.l. in a mild
boreal climate, by the Sognefjord, Norway. Our goal was to investigate the
variation in reproductive success and pollen limitation in a functionally
important plant species, V. myrtillus, and to test whether the outcomes
may be dependent on insect flower visitation and climatic context (i.e.
temperature related to elevation). Our experimental treatments clearly
affected reproductive success of V. myrtillus. Bagging of flowers reduced
the fruit set close to zero, whereas supplemental pollination resulted in
30% higher fruit set. However, fruit set effects appeared to be
independent of elevation in the current study. Total number of seeds was
highest at the optimal mid-site location, but here the proportion of
mature seeds was also lowest. Our results clearly showed that the
reproductive success of V. myrtillus depends on pollinator visitation and
benefits from extra pollen supply, but that these effects appeared to be
independent of the climatic context.