1,720,961 research outputs found
Branch xylem vascular adjustments in European beech in response to decreasing water availability across a precipitation gradient
No full textAbstract
Crucial for the climate adaptation of trees is a xylem anatomical structure capable of adjusting to changing water regimes. Although species comparisons across climate zones have demonstrated anatomical change in response to altered water availability and tree height, less is known about the adaptability of tree vascular systems to increasing water deficits at the intraspecific level. Information on the between-population and within-population variability of xylem traits helps assessing a species’ ability to cope with climate change. We investigated the variability of wood anatomical and related hydraulic traits in terminal branches of European beech (Fagus sylvatica L.) trees across a precipitation gradient (520–890 mm year−1) and examined the influence of climatic water balance (CWB), soil water capacity (AWC), neighborhood competition (CI), tree height and branch age on these traits. Furthermore, the relationship between xylem anatomical traits and embolism resistance (P50) was tested. Within-population trait variation was larger than between-population variation. Vessel diameter, lumen-to-sapwood area ratio and potential conductivity of terminal branches decreased with decreasing CWB, but these traits were not affected by AWC, whereas vessel density increased with an AWC decrease. In contrast, none of the studied anatomical traits were influenced by variation in tree height (21–34 m) or CI. Branch age was highly variable (2–22 years) despite equal diameter and position in the flow path, suggesting different growth trajectories in the past. Vessel diameter decreased, and vessel density increased, with increasing branch age, reflecting negative annual radial growth trends. Although vessel diameter was not related to P50, vessel grouping index and lumen-to-sapwood area ratio showed a weak, though highly significant, positive relationship to P50. We conclude that the xylem anatomy of terminal tree-top branches in European beech is modified in response to increasing climatic aridity and/or decreasing soil water availability, independent of a tree height effect.</jats:p
The Future of European Beech in Northern Germany—Climate Change Vulnerability and Adaptation Potential
No full textOpen-Access-Publikationsfonds 202
A genome-wide genetic association study reveals SNPs significantly associated with environmental variables and specific leaf area in European beech
No full textEuropean beech is negatively affected by climate change and a further growth decline is predicted for large parts of its distribution range. Despite the importance of this species, little is known about its genetic adaptation and especially the genetic basis of its physiological traits. Here, we used genotyping by sequencing to identify SNPs in 43 German European beech populations growing under different environmental conditions. In total, 28 of these populations were located along a precipitation and temperature gradient in northern Germany, and single tree-based hydraulic and morphological traits were available. We obtained a set of 13,493 high-quality SNPs that were used for environmental and SNP-trait association analysis. In total, 22 SNPs were identified that were significantly associated with environmental variables or specific leaf area (SLA). Several SNPs were located in genes related to stress response. The majority of the significant SNPs were located in non-coding (intergenic and intronic) regions. These may be in linkage disequilibrium with the causative coding or regulatory regions. Our study gives insights into the genetic basis of abiotic adaptation in European beech, and provides genetic resources that can be used in future studies on this species. Besides clear patterns of local adaptation to environmental conditions of the investigated populations, the analyzed morphological and hydraulic traits explained most of the explainable genetic variation. Thus, they could successfully be altered in tree breeding programs, which may help to increase the adaptation of European beech to changing environmental conditions in the future
Soil water availability and branch age explain variability in xylem safety of European beech in Central Europe
No full textXylem embolism resistance has been identified as a key trait with a causal relation to drought-induced tree mortality, but not much is known about its intra-specific trait variability (ITV) in dependence on environmental variation. We measured xylem safety and efficiency in 300 European beech (Fagus sylvatica L.) trees across 30 sites in Central Europe, covering a precipitation reduction from 886 to 522 mm year−1. A broad range of variables that might affect embolism resistance in mature trees, including climatic and soil water availability, competition, and branch age, were examined. The average P50 value varied by up to 1 MPa between sites. Neither climatic aridity nor structural variables had a significant influence on P50. However, P50 was less negative for trees with a higher soil water storage capacity, and positively related to branch age, while specific conductivity (Ks) was not significantly associated with either of these variables. The greatest part of the ITV for xylem safety and efficiency was attributed to random variability within populations. We conclude that the influence of site water availability on P50 and Ks is low in European beech, and that the high degree of within-population variability for P50, partly due to variation in branch age, hampers the identification of a clear environmental signal
Adjustment of hydraulic, anatomical and leaf traits in Fagus sylvatica (L.) towards drier conditions. A study in mature stands.
Full text linkHydraulic traits are closely linked to the ability of tree species to survive droughts and were therefore used to predict the disposition of trees to suffer from hydraulic failure in the face of climate change. While most studies focus on inter-specific differences in functional traits, less is known about the variability within tree species as well as within populations and about the factors influencing this variability. The species investigated in the presented thesis, European beech (F. sylvatica) is the most abundant tree species of Central Europe’s natural forest vegetation and an important timber species for many countries. Despite its wide distribution range and the tolerance of a broad variety of climatic and edaphic growth conditions, European beech is known to be relatively drought sensitive. However, a high capacity to adapt to changing climatic conditions was suggested for this species due to a high intra-specific variability in hydraulic traits.
To assess the species’ adaptive and acclimative potential to drier conditions and to support the identification of potentially drought-hardier provenances, this study provides a large dataset on xylem hydraulic, anatomical and leaf traits of upper-canopy branches collected from 300 beech trees growing on 30 different sites in the lowlands of northern Germany between the North Sea coast and the Polish border. A comprehensive approach to describe the water availability across the gradient was used by including the climatic water balance (CWB) or 60-year mean annual precipitation (MAP, in case of leaf traits), as well as the plant-available water capacity of the soils (AWC) and competition between neighbouring trees (CI) in the analyses. Furthermore, the effect of branch age on xylem hydraulic and anatomical traits and the effect of tree height on anatomy were considered. As sampling was conducted in the summers of 2018 and 2019, data on leaf traits were analysed for the two years separately and results were compared between the two years. The portion of trait variation attributed to the above-mentioned variables as well as the degree of between- and within- population variability were quantified.
The effect of water availability on xylem traits was rather low. Embolism resistance and vessel density were significantly related to AWC, while vessel diameter, lumen-to-sapwood area ratio and potential conductivity decreased significantly with decreasing CWB. Xylem-specific hydraulic conductivity was not affected by water availability. In contrast to the xylem traits, leaf traits showed considerable plasticity in response to climatic and edaphic aridity, with differing effects of water availability between the sampling years 2018 and 2019. For the 2018 data set, an increase in mean leaf size (LS) and a decrease in the sapwood-to-leaf area ratio (Huber value, HV) towards drier conditions was observed, indicating that water supply to the sun canopy foliage is not improved upon precipitation reduction. However, this relationship was not pronounced in the 2019 data set, instead, specific leaf area (SLA) and water potential at turgor loss point (Ptlp) were adjusted towards drier sites. Furthermore, carbon isotope signature and Ptlp were modified in response to short-term CWB. While xylem traits were not related to tree height, branch age, which varied considerably by 20 years in branches of comparable diameter, had a major influence on most of the xylem traits. Embolism resistance and vessel diameter significantly decreased, whereas vessel density increased with increasing branch age. Vessel diameter was not significantly related to embolism resistance, but vessel grouping index and the lumen-to-sapwood area ratio showed a weak but significant relation. Within-population variability was larger than between-population variability for all investigated traits except for SLA and Ptlp of the 2019 data set.
Our results suggest that (1) anatomical modifications in response to water availability are rather a growth consequence of water limitation than an active acclimative response in order to increase hydraulic safety, and that (2) these modifications in terminal branches are independent of tree height. The rather small influence of water availability on embolism resistance and the high portion of unexplained variability suggest a minor acclimative capacity in this trait and indicate that embolism resistance might not be a promising trait for the identification of drought-resistant provenances. Overall, leaf traits appear to be under stronger environmental control than xylem traits. The increase in LS and decrease in HV with decreasing precipitation enhances the drought stress exposure of sun foliage at drier sites. Yet, under water shortage, osmotic adjustment to local water availability might be an important acclimative response in European beech.2022-08-3
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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