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(1) Current climate changes can led to a decline of local beech populations fully adapted to previous climate conditions. In this context, the issue of variation in adaptive traits becomes important. A field experiment with 18-year-old trees of Fagus sylvatica L. was conducted on provenance plot located in Tále (Central Slovakia), where physiological responses of five beech provenances originating from contrasting sites along an altitudinal gradient from 55 to 1100 m a.s.l. across the range of the natural beech distribution were studied. Stomatal characteristics, parameters of chlorophyll a fluorescence and gas exchange parameters were determined. Overall, we observed a significant increase in physiological performance at the leaf level with increasing altitude of origin. Provenances from the higher altitudes showed higher CO2 assimilation rate, stomatal density, potential conductance indices and photochemical efficiency, and lower capability for dissipation of energy by heat. A similar pattern of response was recorded in relation to the precipitation regime of sites of origin. Moreover, in the context of the temperature regime, several negative trends were observed.

Research Highlights: In this study, we found different regulatory mechanisms in two contrasting provenances of Norway spruce responding to progressive drought stress. Background and Objectives: In the context of climate and environmental changes, the following question of high importance in scientific studies is: How will Norway spruce, which forms a dominant component in European mountain and boreal forests, be able to cope with the increasing frequencies and intensities of drought periods? The aim of the study was to investigate the physiological responses of eight-month-old seedlings, as a most vulnerable phase of forest tree life, for different spruce provenances, to find out variable strategies in relation to controlled drought stress. Materials and Methods: We performed an experiment under controlled conditions with spruce seedlings from a climatologically warmer stand of 410 m above sea level (a.s.l.), and a moderately cool stand of 931 m a.s.l. The soil water content, leaf predawn water potential, the osmotic potential of needles, the relative water content of needles, and the photosynthetic performance and the contents of primary metabolites (proline and abscisic acid) were investigated as indicators of the spruce seedlings’ responses to water stress. The status of the indicators was analyzed at different temporal intervals, using repeated measures analysis of variance (ANOVA), reflecting the seedlings´ water conditions (early drought, drought, or recovery). On a daily basis, the differences among the indicators were tested with one-way ANOVA. A principal component analysis (PCA) was used to identify the provenance-specific responses of tree drought indicators in a multi-dimensional data set. Results: The responses to drought stress differed between the provenances. Whereas seedlings of ´warm´ provenance from a low altitude performed a conservation strategy, with high amounts of accumulated abscisic acid and closing the stomata faster, the reactions of ´cool´ provenance seedlings from a higher altitude were not so sensitive and the plants’ water supply and photosynthetic performance remained significantly higher. These findings indicate that a higher drought resistance in ´cool´ provenance could be related to greater amounts of proline amino-acids, which are accumulated from the beginning of the drought simulation. Furthermore, proline accumulation resulting in increased stress tolerance is controlled through another mechanism than osmotic adjustment. Conclusions: The observed variations in the regulatory mechanisms used to develop adaptive strategies in different provenances are an important factor for seedling survival under a changing climate.

Understanding of the intraspecific variability in the physiological stress response of trees may enable to mitigate the impact of climate change on forest ecosystems in the future. We studied the photosynthetic performance of five silver fir (Abies alba Mill.) provenances originating from climatically distinct localities. The study was performed in the trial plot of the silver fir provenance experiment IUFRO 2005 on two dates: in the early summer and in the late summer. Heat waves and a decrease in water availability occurred between the two measurement dates, allowing us to study the response of the provenances to suboptimal growing conditions. The provenances were evaluated at the level of PSII photochemistry and CO2 assimilation by measuring photosynthesis-related pigment content, chlorophyll a fluorescence, and gas exchange parameters. Significant climatic clines were confirmed: the photosynthetic performance before and after the stress period increased with the increasing altitude and precipitation at the site of origin. In contrast, photosynthetic performance declined with the increasing temperature and Ellenberg’s quotient of the origin site. We concluded that provenances originating from high altitudes, corresponding well with more humid and colder conditions in Central Europe, showed the greatest photosynthetic performance and were less responsive to moderate heat and drought. This documents inter-population variation in physiological traits, which needs to be considered in setting rules and recommendations for the transfer of forest reproductive materials.

1. Hypophysiotropic thyrotropin-releasing hormone (TRH) is synthesized in the hypothalamic paraventricular nucleus (PVN) and transported to the median eminence (ME) where it enters the hypophyseal portal blood. TRH in the ME is situated exclusively in nerve terminals, whereas TRH in the PVN and septum is of extrinsic (nerve terminals) as well as intrinsic (perikarya) origin. 2. To determine the source and possible differential regulation of TRH release from these structures, we blocked TRH axonal delivery by i.c.v. administration of colchicine into the lateral cerebral ventricle of euthyroid or hypothyroid rats in doses of 7.5 mug or 7.5, 75 and 100 microg, respectively, two days prior to the evaluation of the TRH secretion from the PVN, ME and the septum in vitro. 3. In euthyroid rats a low dose of colchicine did not significantly affect plasma TSH. The secretory response to both ethanol in an isosmolar medium and a high K+ in the ME as well as the PVN explants was well preserved. However, colchicine treatment resulted in the significant increase of basal secretion of TRH from the PVN. 4. Hypothyroidism induced by 200 mg/l methimazole in drinking water for two weeks resulted in growth arrest, elevated plasma thyrotropin and decreased TRH content in the PVN and the ME. Colchicine partially decreased elevated plasma thyrotropin and increased the TRH content in the PVN and its basal release in vitro which was independent of extracellular Ca2+. Interestingly, a TRH release from the PVN could not be further stimulated either by K+ membrane depolarization or by ethanol. TRH responsiveness to the stimulation remained unaffected in the ME. The effect of colchicine on the septal TRH secretion was intermediate between the effect observed in the PVN and the ME. 5. In conclusion, the absence of a TRH secretory response to stimuli in the PVN after colchicine disruption of the microtubules and Golgi system suggests that stimulated TRH release observed from the PVN explants in vitro occurs from nerve terminals projecting to the PVN from other brain regions. The independence from extracellular calcium implies that TRH released under the non-stimulating conditions occurs most likely via the constitutive secretory pathway from dendrites and/or perikarya. Regulation of septal TRH is markedly different from the hypophysiotropic one.

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The aims of this study were to test if ethanol induces thyrotropin-releasing hormone (TRH) secretion in vitro from the posterior pituitary and hypothalamic explants by a mechanism involving cell swelling, and to characterize the pathway of stimulated secretion. Ethanol, at a concentration of 80 mM, stimulated the release of TRH from the posterior pituitary, the hypothalamic paraventricular nucleus, the median eminence, and the brain septum, when administered only in isosmolar but not in hyperosmolar medium. This indicates the involvement of a cell swelling-inducing mechanism. L-canavanine in a concentration of 3 mM, increased the basal and hyposmosis-induced TRH secretion from the posterior pituitary and the paraventricular nucleus, and both basal and ethanol-induced TRH secretion from isolated pancreatic islets. This indicates the presence of both constitutive and regulatory secretory pathways. Our results suggest that cell swelling induces exocytosis from clathrin coated granules.