Elevational Variation in Morphology and Biomass Allocation of Alpine Yellow-Violet Viola biflora

Mountain plants spanning broad elevational ranges experience changes in climate, vegetation structure and biotic interactions that may generate contrasting trait responses. We investigated elevational variation in morphology and aboveground biomass allocation of Viola biflora across its range in the Polish Tatra Mountains. A total of 338 flowering individuals were sampled at 34 sites between 890 and 2115 m a.s.l. Traits were analysed using mixed-effects models comparing straight-line and quadratic relationships with elevation. Plant height, plant mass, stem mass and rosette and stem leaf petiole length showed hump-shaped relationships, with maxima around the middle of the elevational range. Plant height increased by 22.9% to its maximum and then decreased by 34.1%, while stem leaf petiole length increased by 75.6% before declining by 34.5%. Leaf mass and stem leaf blade area decreased continuously with elevation. Flower mass did not vary significantly, whereas corolla length and width decreased by 15.5% and 19.6%, respectively. Flower mass fraction was lowest at intermediate elevations and increased towards the highest sites. Mid-elevation maxima in plant height and petiole length coincided with the transition from forest understorey to open subalpine vegetation and may reflect changes in light availability and interactions with neighbouring vegetation.