Altitudinal differences in flower traits and reproductive allocation

We tested whether alpine plants increase their effort to attract pollinators to compensate for assumed pollinator scarcity at high altitude. A three times larger fraction of the shoot was allocated to flowers in alpine plants (30 species, 2700 m asl) compared to lowland plants (20 species, 600 m asl), while leaf mass fraction did not differ between the altitudes. At high elevation, a three times smaller fraction of the shoot was allocated to stems, which was accompanied by a change in its function from leaf support for photosynthesis at low altitude to support for flowers at high altitude. Although shoot mass is massively reduced at high altitudes, display area and biomass of individual flowers were remarkably similar at both altitudes. All flowers together attracted pollinators with about the same total display area relative to overall plants size, but generally alpine plants maintain their flowers longer. Together with decreased plant height this leads to an increased self-shading which is likely to cause reductions in carbon gain in alpine plants. The results of this field survey emphasize the importance of outcrossing in alpine plants and its priority over growth.