Complex Responses to Climate Warming of Arctic-Alpine Plant Populations From Different Geographic Provenance.

The distribution of 'cold-adapted' plant species is expected to undergo severe range loss in the near future. Species distribution models predicting species' future distribution often do not integrate species ability to respond to environmental factors through genetic traits or phenotypic plasticity. This especially applies to arctic-alpine species whose present-day range is strongly fragmented because of the cyclic vicissitudes they experienced during the Ice Age. We cultivated plants from four European populations of the arctic-alpine species from different geographic provenances. Two of the populations were from northern high-latitude regions in Scandinavia; the remaining two populations were from southern mid-latitude mountains. In both areas, one population was from a colder site and the other from a warmer site. We cultivated the plants in controlled thermal conditions with two treatments, one mimicking temperature conditions at the warmest site and the other adding 2 day-temperature peaks mimicking short-term heat waves. At the end of the experiment, we measured growth in length and mortality of all plants along with a set of ecophysiological variables. We also assessed phylogeographic variation in the four populations based on plastid-DNA sequences. The plants from northern provenances grew more than those from the southern provenances. The plants of all populations performed overall well, in terms of growth rate and ecophysiology, under the heat spell, with the plants of the Swedish population exhibiting the highest phenotypic plasticity. Such a pattern was associated with the highest genetic variation in the Swedish population. Mortality of the plants cultivated under warm temperatures was overall low, but mortality strongly increased in the plants exposed to the heat spell. We conclude that plants of populations from different geographic provenances are generally able to cope with scenarios resulting from global warming, but drought hampers resilience to heat waves through increased mortality.