Unexpected Vulnerability to High Temperature in the Mediterranean Alpine Shrub Erysimum scoparium (Brouss. ex Willd.) Wettst

Abstract

Current understanding of the effects of extreme temperature on alpine evergreens is very limited for ecosystems under Mediterranean climate (characterised by a drought period in summer), despite being exceptionally biodiverse systems and highly vulnerable under a global change scenario. We thus assessed (i) seasonal change and (ii) effect of ontogeny (young vs. mature leaves) on thermal sensitivity of Erysimum scoparium, a keystone evergreen of Teide mountain (Canary Islands). Mature leaves were comparatively much more vulnerable to moderately high leaf-temperature (≥+40 and <+50 °C) than other alpine species. Lowest LT50 occurred in autumn (−9.0 ± 1.6 °C as estimated with Rfd, and −12.9 ± 1.5 °C with Fv/Fm). Remarkably, young leaves showed stronger freezing tolerance than mature leaves in spring (LT50 −10.3 ± 2.1 °C vs. −5.6 ± 0.9 °C in mature leaves, as estimated with Rfd). Our data support the use of Rfd as a sensitive parameter to diagnose temperature-related damage in the leaves of mountain plants. On a global change scenario, E. scoparium appears as a well-prepared species for late-frost events, however rather vulnerable to moderately high temperatures.

Thermal tolerance of tropical and temperate alpine plants suggests that ‘mountain passes are not higher in the tropics’

“…The freezing resistance of temperate plants is lowest during the peak of summer when it is similar to the resistance observed in tropical plants (Figure 3), consistent with earlier studies (Bannister, 2007;Bannister et al, 2005;Sklenář, 2017). The seasonal acclimation to low temperatures in temperate alpine plants is not accompanied by acclimation to high temperatures, again supporting earlier studies (Buchner & Neuner, 2003;González-Rodríguez et al, 2021;Larcher et al, 2010;Pereira-Castro et al, 2018). Whether the acclimation to high temperatures in tropical alpine plants may be linked to yearly variations in precipitation, daily temperature oscillation or other factors (Buchner et al, 2017;Sklenář et al, 2015) remains to be examined.…”

“…The heat resistance reported for temperate alpine plants ranges between 41–55 °C during the growing season (Buchner & Neuner, 2003; González‐Rodríguez et al, 2021; Körner, 2003; Neuner et al, 2000) and does not seem to differ from the heat resistance range of tropical alpine plants, which is reported to be between 45–54 °C (Leon‐Garcia & Lasso, 2019). We found heat resistance values (ranging from 43.2 to 55.5 °C) that were consistent with the earlier reports for temperate species, but about one third of our resistance values for tropical species (ranging from 35.1 to 54.7 °C) fell below the earlier reported range limit.…”