Abstract
In mountain regions, topological differences on the microscale can strongly affect microclimate and may counteract the average effects of elevation, such as decreasing temperatures. While these interactions are well understood, their effect on plant adaptation is understudied.We investigated winter frost hardiness of Arabidopsis thaliana accessions originating from 13 sites along altitudinal gradients in the Southern Alps during three winters on an experimental field station on the Swabian Jura and compared levels of frost damage with the observed number of frost days and the lowest temperature in eight collection sites.We found that frost hardiness increased with elevation in a log‐linear fashion. This is consistent with adaptation to a higher frequency of frost conditions, but also indicates a decreasing rate of change in frost hardiness with increasing elevation. Moreover, the number of frost days measured with temperature loggers at the collection sites correlated much better with frost hardiness than the elevation of collection sites, suggesting that populations were adapted to their local microclimate. Notably, the variance in frost days across sites increased exponentially with elevation. Together, our results suggest that strong microclimate heterogeneity of high alpine environments can preserve functional genetic diversity among small populations.Synthesis: Here, we tested how plant populations differed in their adaptation to frost exposure along an elevation gradient and whether microsite temperatures improve the prediction of frost hardiness. We found that local temperatures, particularly the number of frost days, are a better predictor of the frost hardiness of plants than elevation. This reflects a substantial variance in frost frequency between sites at similar high elevations. We conclude that high mountain regions harbor microsites that differ in their local microclimate and thereby can preserve a high functional genetic diversity among them. Therefore, high mountain regions have the potential to function as a refugium in times of global change.
Highlights
In sessile organisms like plants local adaptation along environmental gradients such as aridity or temperature gradients may lead to clinal trait variation
We investigated winter frost hardiness of Arabidopsis thaliana accessions originating from 13 sites along altitudinal gradients in the Southern Alps during three winters on an experimental field station on the Swabian Jura and compared levels of frost damage with the observed number of frost days (
Accessions from higher altitude are more frost resistant Our common garden experiment showed that frost damage significantly decreased with increasing altitude of the collection site if values were averaged across all three experiments (b=-19.2, CrI 95%: -32.8; -5.8)
Summary
In sessile organisms like plants local adaptation along environmental gradients such as aridity or temperature gradients may lead to clinal trait variation. This raises the question to which extent climatic conditions at higher altitude select for higher freezing tolerance and to which extent plants use sites with a warm microclimate, or “microrefugia” (Dobrowski, 2011b), to avoid freezing damage To study this question, we tested frost-hardiness of A. thaliana plants from Southern Alps in the provinces Bolzano and Trento, collected from sites ranging in altitude from 280 to 2,355 meters above sea level. (3) Altitude is a better predictor of frost frequency at low-altitude sites than at high altitudes To test these hypotheses, we included a larger number of populations from the Southern Alps collected at different altitudes and microsites to compare the role of different spatial scales in adaptation to altitude
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