Tage der Biodiversität 2027

Climate change is intensifying the frequency and severity of heat waves, posing significant challenges to plant survival, particularly in alpine ecosystems. Elevated leaf temperatures combined with reduced water availability disrupt physiological processes, but the chronology of these events remains unclear. Here, we investigated the chronology of heat stress responses in three alpine plant species from contrasting habitats: Kalmia procumbens, Rhododendron ferrugineum, and Ranunculus glacialis. We assessed stomatal responses (g_s), changes in cuticular water permeability (g_min, via gas exchange), molecular aggregation and denaturation using differential scanning calorimetry (DSC), photosystem II (PSII) thermotolerance using chlorophyll fluorescence, and tissue heat damage (LT₅₀).

Across the investigated species, the earliest detectable response to increasing temperature was stomatal opening at approximately 31.9 °C, followed by disturbances of PSII. Stomatal responses occurred around 10 K below the onset of tissue heat damage, potentially enabling leaf cooling under increasing thermal stress. PSII dysfunction was detected shortly before initial tissue damage and thus represents an early indicator of heat stress. In contrast, increased cuticular permeability and bulk molecular denaturation occurred only at substantially higher temperatures, approximately 10 K above the onset of tissue heat damage. The sequence and temperature thresholds of heat stress responses differed among species. R. glacialis exhibited the lowest heat thresholds, followed by R. ferrugineum and K. procumbens, corresponding broadly to increasing heat loads in their natural habitats.

This study emphasizes the importance of a better understanding of heat stress responses in alpine plants, which face disproportionate impacts from climate change. The findings offer key insights into alpine species’ adaptive strategies and suggest that stomatal and molecular heat thresholds may serve as indicators of heat resilience. These insights are critical for improving models of plant responses to global warming, particularly in vulnerable high-altitude ecosystems.