We set out to assess the local adaptation of V. alpina to historical habitat conditions by determining growth rates of plants from different populations grown under temperature conditions currently experienced by the population at the warmest site. Our experimental setup was justified because our goal was to determine how past adaptation affects the response of V. alpina populations to a warming climate. In this study, we did find higher growth rates inV. alpina plants from northern populations grown together with plants of southern populations although the among-population differences of survival rate were overall poor. However, geographic separation between northern and southern provenances did not coincide with climate because mean temperatures at the original location sites considerably differ from each other in both northern and southern areas. So, the observed geographic differences in plant growth could be related to a better capacity of northern populations of V. alpina, a rather drought-sensitive species (Nagy 2013), to cope with reduced water availability (Abeli et al. 2015). This can be caused by lower precipitation at the northern sites and/or by the poor water-holding capacity of the shallow soils that usually characterize the pioneer habitats colonized by northern V. alpina populations (Nagy 2013). Our finding is in line with similar patterns observed in several arctic-alpine species whose northern high-latitude populations have optimum niches in drier conditions than the southern mid-latitude populations (Wasof et al. 2015).
Many studies found significant differences, in terms of several response variables, among populations of different provenance for both herbaceous and woody species, from various bioclimatic regions, grown under common environmental conditions (Blumenthal et al. 2020, Diaz et al. 2022). Similar to our approach, local adaptation of arctic-alpine species has been generally assessed by cultivating plants from thermally differing, geographically more or less distant provenances grown under common warm temperatures that mimicked or exceeded mean air temperature at the warmest collection site (Quan and Wang 2018, Morente-López et al. 2020). A general finding of those studies was that plants originating from colder sites flower earlier, grow faster and have higher survival than plants originating from warmer sites when all plants are cultivated in controlled thermal conditions (DeMarche et al. 2018, Valdés et al. 2019). A pre-requisite for genetically-based local adaptation to occur is that strength of selection overcomes the levelling effect of long-distance dispersal (Yeaman and Whitlock 2011; Eusemann and Liesebach 2021). If this happens, the more active development of plants from colder climates can be interpreted as a counter-gradient historical adaptation to shorter colder growing seasons (Conover and Schultz 1995).