Forest tree provenances have evolved diverse and complex mechanisms to acclimate to changes in environmental conditions. Pedunculate oak (Quercus robur L.), along with other European tree species, is increasingly exposed to the adverse effects of climate change, particularly prolonged drought periods and severe drought stress. Understanding the species’ capacity to acclimate to expected environmental changes requires knowledge of key functional traits linked to drought tolerance, such as leaf structure and gas exchange. To explore the acclimation mechanisms of pedunculate oak provenances to repeated drought events, a study was conducted under controlled conditions with plants from nine provenances spanning a north–south gradient across eastern Europe, from Estonia to Italy. The study consisted of two parts: first, leaf structural traits were analyzed after three years of experimentally induced drought by comparing drought and control treatments; second, both treatments were subjected to subsequent drought to analyze differences in gas exchange trait responses. Results demonstrated ecotypic differentiation among provenances in morphological, but not in gas exchange traits, suggesting that provenance adaptedness to drier habitats is more closely associated with structural than physiological traits. Provenances originating from drier habitats showed lower specific leaf area but also different acclimation to repeated drought events, including a stronger reduction in stomatal density and a smaller increase in leaf dry matter content, compared to provenances from more humid habitats. Gas exchange acclimation occurred through a shift in the strategy of photosynthesis down-regulation. These findings emphasize the importance of investigating multiple functional traits rather than focusing solely on individual key traits.
Škvorc et al. (Sat,) studied this question.