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Evolutionary footprints of cold adaptation in arctic-alpine Cochlearia (Brassicaceae) – evidence from freezing experiments and electrolyte leakage
  • Marcus Koch
Marcus Koch
COS Heidelberg
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Abstract

As global warming progresses, plants may be forced to adapt to drastically changing environmental conditions. Arctic-alpine plants have been among the first to experience the effects of climate change, as regions at high latitudes and elevations are over-proportionally affected by rising temperatures. As a result, cold acclimation and freezing tolerance may become increasingly crucial for the survival of many plants as winter warming events and earlier snowmelt will cause increased exposure to occasional frost. Studying the evolution of cold adaptation allows us to make assumptions about the future responses of different species to climate change. The tribe Cochlearieae from the mustard family (Brassicaceae) offers an instructive system for studying cold adaptation in evolutionary terms, as the two sister genera Ionopsidium and Cochlearia are distributed among different ecological habitats throughout the European continent and the far north into circumarctic regions. By applying an electrolyte leakage assay to leaves, the freezing tolerance of different Ionopsidium and Cochlearia species was assessed by experimentally estimating lethal freezing temperature values (LT50 and LT100), thereby allowing for a comparison of different accessions in their responses to cold. We hypothesized that, owing to varying selection pressures, geographically distant species would differ in freezing tolerance. Despite Ionopsidium being adapted to hot and dry Mediterranean conditions and Cochlearia species preferring cold habitats, all accessions exhibited similar cold responses. Whether this phenomenon has resulted from an evolutionary adaptation of a common ancestor of the two taxa or has evolved from parallel evolution is yet to be investigated. The results presented in this study may, however, indicate that adaptations to different stressors, such as salinity and drought, may confer an additional tolerance to cold; this is because all these stressors induce osmotic challenges, as demonstrated via metabolomic analysis.