ALBERT

Description: Due to climate change, sessile oak (Quercus petraea) seedlings experience an increasing risk of drought during regeneration of forest stands by management practices. The present study was aimed at elucidating the potential of sessile oak seedlings originating from sites with different aridity and nitrogen (N) supply to acclimate to contrasting water availability. For this purpose, a free-air cross-exchange experiment was conducted between a dry and a humid forest stand with high and low soil N contents, respectively, during two consecutive years differing in aridity before harvest. Almost all structural and physiological foliar traits analyzed did not differ consistently between seed origins during both years, when cultivated at the same site. As an exception, the arid provenance upregulated foliar ascorbate contents under drought, whereas the humid provenance accumulated the phenolic antioxidants vescalagin and castalagin (VC) under favorable weather conditions and consumed VC upon drought. Apparently, differences in long-term aridity at the forest sites resulted in only few genetically fixed differences in foliar traits between the provenances. However, structural and physiological traits strongly responded to soil N contents and weather conditions before harvest. Foliar N contents and their partitioning were mostly determined by the differences in soil N availability at the sites, but still were modulated by weather conditions before harvest. In the first year, differences in aridity before harvest resulted in differences between most foliar traits. In the second year, when weather conditions at both sites were considerably similar and more arid compared to the first year, differences in foliar traits were almost negligible. This pattern was observed irrespective of seed origin. These results support the view that leaves of sessile oak seedlings generally possess a high plasticity to cope with extreme differences in aridity by immediate acclimation responses that are even better developed in plants of arid origin.

Description: Drought negatively impacts growth and productivity of plants, particularly in arid and semi-arid regions. Although drought events can take place in summer and winter, differences on the impact of drought on physiological processes between seasons are largely unknown. The aim of this study was to elucidate metabolic strategies of date palms in response to drought in summer and winter season. To identify such differences, we exposed date palm seedlings to a drought-recovery regime, both in simulated summer and winter climate. Leaf hydration, carbon discrimination (∆13C), primary and secondary metabolite composition and contents were analyzed. Depending on season, drought differently affected physiological and biochemical traits of the leaves. In summer, drought induced significantly decreased leaf hydration, concentrations of ascorbate, most sugars, primary and secondary organic acids, as well as phenolic compounds, while thiol, amino acid, raffinose and individual fatty acid contents were increased compared to well-watered plants. In winter, drought had no effect on leaf hydration, ascorbate and fatty acids contents, but resulted in increased foliar thiol and amino acid levels as observed in summer. Compared to winter, foliar traits of plants exposed to drought in summer only partly recovered after re-watering. Memory effects on water relations, primary and secondary metabolites seem to prepare foliar traits of date palms for repeated drought events in summer. Apparently, a well-orchestrated metabolic network, including the anti-oxidative system, compatible solutes accumulation and osmotic adjustment, and maintenance of cell membrane stability strongly reduces the susceptibility of date palms to drought. These mechanisms of drought compensation may be more frequently required in summer.