1,721,056 research outputs found
Drought resistance and drought adaptation of Douglas-fir (Pseudotsuga menziesii) – A review
No full textHydraulic capacitance: Biophysics and functional significance of internal water sources in relation to tree size
No full textComponents of the tree water transport pathway; roots, trunks, branches and leaves; can also serve as water storage compartments and therefore act transiently as intermediate sources of water for transpiring leaves. However, most previous work has focused on gradual depletion and recharge of tree internal water reserves as soil water availability varies over seasonal cycles. This chapter focuses on the underappreciated role that internal water storage plays in stabilizing the physiological function of trees under the dynamic conditions that prevail over the course of a day. Capacitive discharge of water into the transpiration stream can buffer daily fluctuations in xylem tension, thereby diminishing the risk of xylem embolism and hydraulic failure under dynamic conditions. Intrinsic sapwood capacitance and reliance on stored water increase with tree size. An inverse relationship between sapwood capacitance and resistance to embolism across diverse woody species suggests that above a minimum threshold value of capacitance, the tree survives by using capacitance to provide hydraulic safety by buffering fluctuations in tension, rather by relying on xylem structural features that directly reduce vulnerability to embolism. Progress in understanding the physiological role of capacitance in trees is impeded by non-uniformity in the way capacitance is measured and expressed, preventing much of the available information from being synthesized. To remedy this, standard protocols are described for defining and expressing capacitance and water storage capacity.Fil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia. Facultad de Ciencias Naturales. Departamento de Biología; ArgentinaFil: Phillips, Nathan G.. Boston University; Estados UnidosFil: Bucci, Sandra Janet. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia. Facultad de Ciencias Naturales. Departamento de Biología; ArgentinaFil: Meinzer, Frederick C.. United States Department of Agriculture; Estados Unido
Allocation to leaf area and sapwood area affects water relations of co-occurring savanna and forest trees
Full text linkWater availability is a principal factor limiting the distribution of closed-canopy forest in the seasonal tropics, suggesting that forest tree species may not be well adapted to cope with seasonal drought. We studied 11 congeneric species pairs, each containing one forest and one savanna species, to test the hypothesis that forest trees have a lower capacity to maintain seasonal homeostasis in water relations relative to savanna species. To quantify this, we measured sap flow, leaf water potential (ΨL), stomatal conductance (gs), wood density, and Huber value (sapwood area:leaf area) of the 22 study species. We found significant differences in the water relations of these two species types. Leaf area specific hydraulic conductance of the soil/root/leaf pathway (Gt) was greater for savanna species than forest species. The lower Gt of forest trees resulted in significantly lower ΨL and gs in the late dry season relative to savanna trees. The differences in Gt can be explained by differences in biomass allocation of savanna and forest trees. Savanna species had higher Huber values relative to forest species, conferring greater transport capacity on a leaf area basis. Forest trees have a lower capacity to maintain homeostasis in ΨL due to greater allocation to leaf area relative to savanna species. Despite significant differences in water relations, relationships between traits such as wood density and minimum ΨL were indistinguishable for the two species groups, indicating that forest and savanna share a common axis of water-use strategies involving multiple traits.Fil: Gotsch, Sybil G.. University of North Carolina; Estados UnidosFil: Geiger, Erika L.. University of North Carolina; Estados UnidosFil: Franco, Augusto C.. Universidade do Brasília; BrasilFil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Meinzer, Frederick C.. United States Forest Service; Estados UnidosFil: Hoffmann, William A.. University of North Carolina; Estados Unido
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
Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species
Full text linkAdaptations of species to capture limiting resources is central for understanding structure and function of ecosystems. We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern Argentina to understand how soil water availability and rooting depth determine their hydraulic architecture. Soil water content and potentials, leaf water potentials (ΨLeaf), hydraulic conductivity, wood density (ρw), rooting depth, and specific leaf area (SLA) were measured during two summers. Water potentials in the upper soil layers during a summer drought ranged from -2.3 to -3.6 MPa, increasing to -0.05 MPa below 150 cm. Predawn ΨLeaf was used as a surrogate of weighted mean soil water potential because no statistical differences in ΨLeaf were observed between exposed and covered leaves. Species-specific differences in predawn ΨLeaf were consistent with rooting depths. Predawn ΨLeaf ranged from -4.0 MPa for shallow rooted shrubs to -1.0 MPa for deep-rooted shrubs, suggesting that the roots of the latter have access to abundant moisture, whereas shallow-rooted shrubs are adapted to use water deposited mainly by small rainfall events. Wood density was a good predictor of hydraulic conductivity and SLA. Overall, we found that shallow rooted species had efficient water transport in terms of high specific and leaf specific hydraulic conductivity, low ρw, high SLA and a low minimum ΨLeaf that exhibited strong seasonal changes, whereas deeply rooted shrubs maintained similar minimum ΨLeaf throughout the year, had stems with high ρw and low hydraulic conductivity and leaves with low SLA. These two hydraulic syndromes were the extremes of a continuum with several species occupying different portions of a gradient in hydraulic characteristics. It appears that the marginal cost of having an extensive root system (e.g., high ρw and root hydraulic resistance) contributes to low growth rates of the deeply rooted species.Fil: Bucci, Sandra Janet. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Goldstein, Guillermo Hernan. Universidad de Buenos Aires; Argentina. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Meinzer, Frederick C.. United States Department of Agriculture; Estados UnidosFil: Arce, Maria Elena. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin
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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