1,721,053 research outputs found
Repeated summer drought delays sugar export from the leaf and impairs phloem transport in mature beech
No full textPhloem sustains maintenance and growth processes through transport of sugars from source to sink organs. Under low water availability, tree functioning is impaired, i.e., growth/photosynthesis decline and phloem transport may be hindered. In a 3-year throughfall exclusion (TE) experiment on mature European beech (Fagus sylvatica L.) we conducted 13CO2 branch labeling to investigate translocation of recently fixed photoassimilates under experimental drought over 2 years (2015 and 2016). We hypothesized (H1) that mean residence time of photoassimilates in leaves (MRT) increases, whereas (H2) phloem transport velocity (Vphloem) decreases under drought. Transport of carbohydrates in the phloem was assessed via δ13C of CO2 efflux measured at two branch positions following 13CO2 labeling. Pre-dawn water potential (ΨPD) and time-integrated soil water deficit (iSWD) were used to quantify drought stress. The MRT increased by 46% from 32.1 ± 5.4 h in control (CO) to 46.9 ± 12.3 h in TE trees, supporting H1, and positively correlated (P < 0.001) with iSWD. Confirming H2, Vphloem in 2016 decreased by 47% from 20.7 ± 5.8 cm h-1 in CO to 11.0 ± 2.9 cm h-1 in TE trees and positively correlated with ΨPD (P = 0.001). We suggest that the positive correlation between MRT and iSWD is a result of the accumulation of osmolytes maintaining cell turgor in the leaves under longer drought periods. Furthermore, we propose that the positive correlation between Vphloem and ΨPD is due to a lower water uptake of phloem conduits from surrounding tissues under increasing drought leading to a higher phloem sap viscosity and lower Vphloem. The two mechanisms increasing MRT and reducing Vphloem respond differently to low water availability and impair trees' carbon translocation under drought
Hydraulische Eigenschaften von Rotbuche und Gemeiner Fichte unter experimentellem Trockenstress
Full text linkDrought responses, hydraulic acclimation and embolism repair potential were investigated in European beech and Norway spruce trees. In adult trees subjected to through-fall exclusion over two years, acclimation of branch and leaf hydraulic traits was found in both species. In drought-irrigation cycles in potted saplings, embolism dynamics were related to stem non-structural carbohydrate content: only spruce recovered stem hydraulic function upon drought stress relief, which was connected to carbohydrate depletion.Hydraulische Akklimatisierung gegen Trockenstress und Wiederherstellung der hydraulischen Leitfähigkeit wurden bei Rotbuche und Fichte untersucht. In ausgewachsenen Bäumen, die über einen Zeitraum von zwei Jahren künstlichem Trockenstress ausgesetzt waren, konnte eine Akklimatisierung in Zweigen und Blättern von beiden Baumarten nachgewiesen werden. In Trockenstress-Wiederbewässerungs-Zyklen wurde bei Topfpflanzen Emboliebildung mit Gehalt an nicht-strukturellen Kohlenhydraten verknüpft: nach Wiederbewässerung wurde nur bei Fichte Emboliereparatur festgestellt begleitet von Kohlenhydratabbau
Mitigation of drought by thinning: Short-term and long-term effects on growth and physiological performance of Norway spruce (Picea abies)
No full textWe hypothesize that reductions in stand density through thinning improve the recovery of radial stem growth in Norway spruce trees (Picea abies) from severe drought. However, thinning may not lead to higher relative radial growth during drought. Annual stem growth and stable carbon and oxygen isotopes in early- and latewood were assessed in trees from heavily thinned (HT), moderately thinned (MT) and un-thinned control stands at two sites in southern Germany. Physiological performance of trees as inferred from stable isotope analysis was used to interpret annual stem growth in response to the drought events in 1976 and 2003. Only in recently thinned stands, trees maintained growth probably through higher soil water availability during the drought year when compared to controls. In contrast, thinning improved the growth recovery in the years following the drought irrespective of the time span between thinning and drought. We conclude that thinning improves drought recovery response in the short and long term and should be considered as an effective management strategy to increase drought tolerance of Norway spruce stands
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
Hydraulic redistribution under moderate drought among English oak, European beech and Norway spruce determined by deuterium isotope labeling in a split-root experiment
No full textHydraulic redistribution (HR) of soil water through plant roots is a crucial phenomenon improving the water balance of plants and ecosystems. It is mostly described under severe drought, and not yet studied under moderate drought. We tested the potential of HR under moderate drought, hypothesizing that (H1) tree species redistribute soil water in their roots even under moderate drought and that (H2) neighboring plants are supported with water provided by redistributing plants. Trees were planted in split-root systems with one individual (i. e., split-root plant, SRP) having its roots divided between two pots with one additional tree each. Species were 2-to 4-year-old English oak (Quercus robur L.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). A gradient in soil water potential (psi(soil)) was established between the two pots (-0.55 +/- 0.02MPa and -0.29 +/- 0.03MPa), and HR was observed by labeling with deuterium-enriched water. Irrespective of species identity, 93% of the SRPs redistributed deuterium enriched water from the moist to the drier side, supporting H1. Eighty-eight percent of the plants in the drier pots were deuterium enriched in their roots, with 61 +/-6% of the root water originating from SRP roots. Differences in HR among species were related to their root anatomy with diffuse-porous xylem structure in both beech and-opposing the stem structure-oak roots. In spruce, we found exclusively tracheids. We conclude that water can be redistributed within roots of different tree species along a moderate.soil gradient, accentuating HR as an important water source for drought-stressed plants, with potential implications for ecohydrological and plant physiological sciences. It remains to be shown to what extent HR occurs under field conditions in Central Europe
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
from leaf level water use efficiency to stand and area scale assessments
Full text linkAktuelle Klimamodelle prognostizieren, dass viele bedeutendeWaldregionen in Mitteleuropa zukünftig einer steigenden Frequenz und höheren Intensität von Dürreperioden ausgesetzt sein werden. Buchendominierte Wälder bilden einen wichtigen Bestandteil dieser Waldregionen. Der Mangel hinsichtlich der Wasserversorgung ist eine der wichtigsten limitierenden Faktoren für das Wachstum der Pflanzen sowie der damit verbundene reduzierte Zugewinn an Kohlenstoff. Ein weiterer bedeutender Stressfaktor ist die Konkurrenz zwischen sowie innerhalb Pflanzengemeinschaften. Aufgrund dieser Tatsache ist es wichtig, die pflanzenphysiologischen Mechanismen während der Trockenheit sowie interspezifische und intra-spezifische Konkurrenz in buchendominierten Waldökosystemen zu verstehen. Die vorliegende Arbeit untersucht den Zusammenhang von Kohlenstoff- und Wasserhaushalt und deren Wechselwirkungen sowie die Transportwege während der Trockenheit auf unterschiedlichen räumlichen (Blattebene bis Bestandesebene) und zeitlichen (kurzfristig bis langfristig) Skalen. Insgesamt wurden sechs Arten ausgewählt (Fagus sylvatica, Acer platanoides, Fraxinus excelsior, Impatiens noli tangere, Mercurialis annua und Allium ursinum). Alle Arten haben verschiedene Strategien entwickelt, um Konkurrenz und Trockenstress zu bewältigen, zu verhindern oder zu tolerieren. In Abhängigkeit von der Trockenstressintensität wurden geringe Effekte, in der Mesophyllleitfähigkeit (gm), intrinsische Wassernutzungseffizienz (iWUE) sowie in der Transportmenge an neuen Assimilaten beobachtet.Current climate models predict that many important forest regions in Central Europe will experience increasing frequencies and severities of drought periods. Beech-dominated forests are an important part of these forest regions. Shortage in water supply is one of the most important limiting factors for growth of plants and thereby linked to a reduced carbon gain. Another key stressor is the competition between as well as within a plant communities. Due to this fact it is important to understand the plants physiological mechanisms during drought as well as inter-specific and intra-specific competition in beech dominated forest ecosystems. This present study documents the interrelation of carbon and water balance and the interactions of its pathways during drought on different spatial (leaf area to the stand level) and temporal scales (intra-annual to decadal). Six relevant species were selected in total (tree species: Fagus sylvatica, Acer platanoides, Fraxinus excelsior and species from the understorey of beech dominated forests: Impatiens noli tangere, Mercurialis annua and Allium ursinum). All of them have developed various strategies to cope with competition and avoid or tolerate drought stress. Depending on the drought intensity (e.g. moderate realistic drought) small effects in mesophyll conductance (gm), intrinsic water use efficiency (iWUE) and amount of new assimilates within trees occurred
Mature beech and spruce trees under drought – Higher C investment in reproduction at the expense of whole-tree NSC stores
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