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).