Temperature resistance of tropical and temperate alpine plants
Dataset S1: A total of 96 species common in zonal alpine habitats at the study sites (Antisana, Ecuador; Charkirini, Bolivia; Niwot ridge, Colorado; Brennkogel, Austria) and representing different phylogenetic linages and growth forms of vascular plants were studied. Dataset S2: Species distribution data were obtained primarily from GBIF, extracting the northernmost and southernmost occurrences in the Americas.
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Entire plants, twigs or stems, and in a few exceptional cases individual leaves were collected in the field and placed in a thermo-insulated plastic box, transported to the laboratory and kept in the dark at ca 5 °C until measurements were performed within 24 hours from the sampling. Temperature resistance was measured on detached entire leaves, using eight replicates per species in each temperature treatment. Leaves were placed in a freezer in which temperature was controlled within 0.5 °C using a heating unit. Each temperature treatment consisted of 30 minutes acclimation period, temperature decline (increase) at a constant rate of 5 K/hour, 30 minutes exposure to target temperature, temperature increase (decline) at 5 K/hour to the starting (acclimation) temperature. Acclimation temperature was 4 °C for the freezing treatments and 25 °C for the heating treatments. Target temperatures were determined in 4 K intervals between 0 °C (i.e., control temperature producing no injury) and –32 °C for freezing treatments and between 36 °C (control) and 64 °C for heating treatments, although the entire range of target temperatures was not used in all species. The injury, which is proportional to leakage of electrolytes from cells damaged due to excessive temperature, was estimated by the conductivity method. Species distribution data were obtained primarily from GBIF, extracting the northernmost and southernmost occurrences in the Americas. The occurrence data were checked against the reference source and credibility of each record evaluated using our own expert knowledge or by verifying with a specialist for a particular taxonomic group, thereby omitting unsupported records.