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With prolonged periods of drought and temperature extremes becoming more frequent, the stress on Norway spruce has increased, as its ecological optimum is in colder and more humid environments. However, it is a tree species with a good adaptability, due to its great geographic and intraspecific variability. In this study, we tested the sensitivity of chlorophyll a fluorescence tools for the early detection of drought and heat stress, as well as their combined effect, in four Slovak Carpathian provenances, under controlled laboratory conditions. Responses in photosynthetic parameters of fast and slow (light response curves) kinetics of chlorophyll a fluorescence were analysed in spruce seedlings under four treatments: control, drought, heat, and combined drought + heat. Heat and drought + heat stresses led to the decrease of photosynthetic efficiency to a greater extent than in the case of only individual drought stress. The less sensitive parameter impacted by the stresses was the maximum quantum yield of PSII photochemistry (Fv/Fm), while the more sensitive parameters were: the performance index based on absorption of light energy (PIABS), the effective quantum yield of the PSII (ΦPSII), and the coefficients of non-photochemical fluorescence quenching (NPQ, qN). The significant variability in responses of individual provenances was also observed. Seedlings from two studied provenances responded better to these abiotic stresses (Pa-680 and Pa-1500); however, Pa-1500 provenance from the highest altitude showed the best ability of resistance to soil drought stress, as well as to high temperature effect. This rapid screening of photosystems II efficiency showed the importance of the selection of more resistant populations to concurrent stresses as one of the measures to mitigate climate change impacts.

Norway spruce is expected to suffer from drought stress and other manifestations of climate change. This study relies on a manipulative experiment with drought-stressed and well-watered (control) seedlings, comprising five provenances of Norway spruce distributed along a steep elevational transect from 550 to 1,280 m a.s.l. within the natural range. Seedlings were subjected to measurement of physiological traits (content of phytohormones and monoterpenes, slow and fast chlorophyll a fluorescence kinetics, gas exchange, hyperspectral indices), and genotyping at 8 nuclear microsatellite loci. Comparison of the coefficient of differentiation at neutral loci (FST) vs. differentiation at phenotypic traits (PST) was used to identify traits underlying divergent selection. In total, 18 traits exhibited a significant PST – FST difference. However, the consistency in differentiation patterns between drought-stressed and control plants was limited, only three traits exhibited signals of selection under both treatments. This outcome indicates that the identified differentiation patterns can only be interpreted in the context of environmental setup of the experiment, and highlights the importance of common gardens in adaptation research, as they allow both elimination of environment-induced phenotypic variation and studying genotype-by-environment interaction in physiological responses to environmental stresses.

Norway spruce is an ecologically and commercially important species, which currently suffers from climate change and is expected to decline because of heat and drought stress. A manipulative experiment with drought-stressed and well-watered (control) seedlings was established, comprising five populations of Norway spruce coming from a small territory but distributed along a steep elevational transect from 550 to 1280 m.a.s.l. Plants were phenotyped at physiological traits (content of phytohormones and monoterpenes, chlorophyll a fluorescence, gas exchange and hyperspectral indices) and genotyped using ddRAD sequencing. After filtering, 34 127 polymorphisms (SNPs) were retained and used for analysis. Association tests revealed 42 SNP-variable pairs located across 29 scaffolds exhibiting significant associations, among them 20 were found for drought-stressed seedlings and 22 for control (watered) plants. However, there was no consistency between drought-stressed and control plants, no SNP-trait pair was common for both treatments. The study demonstrated that the identified genotype–phenotype associations can only be interpreted in the context of environmental setup preceding the assessment of phenotypic traits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Poplar clones "Robusta" and "I-214" (Populus × euramericana) are characterized by fast growth and high quality biomass production. In this investigation the calorific value of these clones was determined, and modeling of the calorific production of a whole poplar clone stands in relation to stand age and site index was performed. Eleven trees were sampled in four sites in the eastern and seven in the western part of Slovakia. Samples of bark, wood and smallwood with bark were excised from three points along the stem and from two parts of the crown. No significant differences were observed between clones with regard to either the biomass fraction or the excising location. The average calorific capacity of all biomass fractions was approximately 6.86-8.73 GJ m-3, with the lowest bark values obtained for samples excised from the stem base. The mean annual calorific energy production for site index 20-40 was 320-380 GJ ha-1 y-1 after 17-26 years since plantation, with the clone "I-214" culminating 1-2 years earlier than "Robusta". Energy use efficiency of these clones was estimated approximately 0.4-1.6% of the incoming solar radiation. [ABSTRACT FROM AUTHOR]

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The state of mineral nutrition as well as accumulation and translocation of selected heavy metals As, Cr, Hg, and Pb were evaluated in poplar clones Robusta (Populus x euramericana) and I-214 (Populus x euramericana). These clones are characterized by fast growth and biomass production of relatively high quality. Soil water quantity and its dynamics is one of the most important factors for growth of poplar clones, in relation to their high transpiration and nutrient transport. The research was conducted in two locations in eastern and three in western Slovakia. The poplars were grown on alluvial plains continuously influenced by ground waters from surrounding rivers. Differences in As, Cr, and Pb concentrations were recorded among the locations only, whereas between these single-clones no differences were confirmed. Different accumulation patterns were found for some elements (Ca, K, Si) in poplars compared to those of softwood (spruce) and hardwood (beech) species. The mineral elements (Ca, K, Mg, Na, Si) were accumulated in above-ground parts as follows: stem > "small-wood"/bark > wood. Cr was the most represented risk element in biomass, while Hg reached the highest concentrations and in contrast to essential elements was accumulated predominantly in wood. A potential source of Hg was soil/water environment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]