Search

Drought tolerance is becoming an increasingly important criterion for the selection of tree species, especially in urban areas characterized by low water availability. Apart from drought tolerance, the introduction of non-native species should be considered for new planting programs under such conditions to enhance the resilience of urban forests. The present study is aimed at evaluating the in situ physiological responses of Magnolia grandiflora and Magnolia × soulangeana to severe drought that frequently occurs in urban environments in the Southeastern Europe. Transpiration rate, stomatal conductance, intercellular CO2 concentration, water-use efficiency and intrinsic water-use efficiency showed notable differences both between species and between the measured periods (wet and dry). Among the chlorophyll a fluorescence parameters, effective photochemical quantum yield of PS II, quantum yield of lightinduced non-photochemical fluorescence quenching, quantum yield of nonregulated heat dissipation, fluorescence emission and index of susceptibility of leaves to light stress revealed significant differences both between the two species and the periods of measurements. The reduction of net photosynthesis in both magnolia species occurs as the result of non-stomatal limitation obtained by the reduction of electron transport rate coupled with simultaneous increase in intercellular CO2 concentration. Moreover, M. grandiflora was the species less vulnerable to water shortage conditions, while M. soulangeana exhibited a photosynthetic capacity sensitive to drought-induced stress. M. grandiflora can therefore be considered as a promising alternative to M. soulangeana for urban sites under the predicted climate change scenarios. [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]

Frequency and intensity of heat waves and drought events are expected to increase in Europe due to climate change. European beech (Fagus sylvatica L.) is one of the most important native tree species in Europe. Beech populations originating throughout its native range were selected for common-garden experiments with the aim to determine whether there are functional variations in drought stress responses among different populations. One-year old seedlings from four to seven beech populations were grown and drought-treated in a greenhouse, replicating the experiment at two contrasting sites, in Italy (Mediterranean mountains) and Germany (Central Europe). Experimental findings indicated that: (1) drought (water stress) mainly affected gas exchange describing a critical threshold of drought response between 30 and 26% SWA for photosynthetic rate and Ci/Ca, respectively; (2) the Ci to Ca ratio increased substantially with severe water stress suggesting a stable instantaneous water use efficiency and an efficient regulation capacity of water balance achieved by a tight stomatal control; (3) there was a different response to water stress among the considered beech populations, differently combining traits, although there was not a well-defined variability in drought tolerance. A combined analysis of functional and structural traits for detecting stress signals in beech seedlings is suggested to assess plant performance under limiting moisture conditions and, consequently, to estimate evolutionary potential of beech under a changing environmental scenario. [ABSTRACT FROM AUTHOR]

There were studied particular biochemical and physiological characteristics of European beech (Fagus sylvatica L.) saplings of different origin, responding to different water supply. Three different provenances (PV1, PV2, and PV3) representing the lower margin, the upper margin of beech distribution range and the optimal growth and environmental conditions for this species were investigated in a control (well-watered) and a drought treatment. For each provenance, the water potential values (Ψw) towards the end of the experiment were found low, indicating a severe water stress. However, there were not observed significant differences in decreasing Ψw values between the studied provenances. There were also recorded significant decreasing osmotic potential values (Ψs) influenced by drought. In the saplings of the PV2 provenance, the plants deprived of watering (drought treatment) showed the largest decrease of osmotic potential values. All provenances showed significant impacts of drought on the content of assimilatory pigments (Chl a, Chl b, Chl a + b, Chl a/b, Chl/Car). Nevertheless, the observed changes in individual provenances did not differ significantly. The analysis of the response to the controlled water deficit confirmed that the proline content increased significantly for all provenances. The largest increase in the proline concentration was observed in PV2 provenance. These results imply that the most sensitive to water deficit was the provenance PV2 from the optimal ecological beech area. [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]