1,720,958 research outputs found
Structural and functional plasticity of Quercus ilex seedlings of different provenances in Italy
No full textFunctional and structural leaf traits of Quercus ilex seedlings originated from parent plant acorns from three different localities in Italy were studied. Acorns from three different localities along a gradient from the north to the south of Italy: Nago (site A) in the Garda Lake region at the northernmost limit of holm oak distribution area in Italy, Castelporziano near Rome (site B), at the centre of the distribution area, and Frassanito near Otranto (site C), in a drier area in the south of Italy. Morphological and anatomical leaf traits differed between the provenances with a higher leaf mass area, total leaf thickness and the ratio of palisade to mesophyll thickness in the driest provenance (C seedlings). These traits gave C seedlings a higher water use efficiency, relative water content at predawn and photosynthetic rates than the other provenances in high air temperature conditions. The smaller leaf area of A seedlings seemed to have a higher photosynthetic capacity in low air temperature conditions than B and C seedlings. Growth analysis underlined a higher shoot relative growth rate in B seedlings explaining the highest shoot length and leaf number per shoot. The plasticity index [sensu Valladares et al. (2000) Ecology 81:1925-1936] for physiological traits of the seedlings was higher than morphological and anatomical traits, but the largest differences in plasticity among ecotypes were found for morphological and anatomical traits. The ecotypes of Q. ilex studied here seemed to integrate, at leaf level, functions of growth activity, morphology and physiology related to the climate of the original provenance
Responses of Quercus ilex from different provenances to experimentally imposed water stress
No full textResponses of Quercus ilex L. seedlings from three different localities in Italy to experimentally imposed drought stress were analysed. Predawn (Ψpd) and midday (Ψm) leaf water potential of stressed seedlings decreased on an average until -4.0 and -4.2 MPa, respectively, in the severe water stress. At the end of the severe water stress the relative water content (RWC) was 72.5-83.6% and the photosynthetic rates (PN) near zero. The critical threshold value of Ψpd for complete stomatal closure was from -4.0 to -4.5 MPa. The leaf damage after the severe water stress was significantly greater in seedlings originated from the acorns of climax area (45% total leaf injured area and 40% fallen leaves) than in the other seedlings (on an average 20.5% total leaf injured area and 21% fallen leaves)
Edaphic characteristics of Quercus suber woods in Latium.
No full textIn this paper the results are reported of a soil survey done in selected sites of Latium under the most significant Quercus suber woods (Cytiso-Quercetum suberis Testi, Pignatti and Lucattini 1994) previously studied from a phytosociological point of view. After describing the dominant soil type of each area, physical-chemical characteristics have been analysed in order to point out the significance of edaphic factors in the distribution and floristic composition of the Quercus suber coenoses. Bioclimatic, structural and edaphic features of this vegetation showed a great convergence; among all the parameters examined, AWC resulted to be the most effective one in conditioning the mesophilous character of Quercus suber coenoses growing in Latium. In this respect this type of vegetation shows rather strong affinities with mixed Quercus cerris woods, both in the floristic composition and in the edaphic requirements, as already suggested in the most recent phytosociological studies
Analisi della struttura di Pinus pinea L. in funzione dell’età: variazione dell’indice di area fogliare (LAI) e della morfologia degli aghi.
No full textPhotosynthesis as a temperature indicator in Quercus ilex L.
No full textNet photosynthesis (Pn), stomatal conductance (gs), leaf temperature (LT), transpiration rate (E) and in vivo chlorophyll fluorescence were monitored February 1996-February 1997 in Quercus ilex plants growing in the climax area (Rome) and in the Garda lake region. Photosynthetic activity is an appropriate temperature-dependent functional trait linked to plant metabolism and performance. We employed photosynthesis as a stress temperature indicator. Regression analysis showed that in such regional climatic conditions, net photosynthetic rates were primarily correlated with temperature. The introduction of rainfall in the function did not significantly improve the theoretical prevision, in the range of temperature and rainfall analysed. The favourable leaf temperatures allowing 90-100% of the highest photosynthetic rates were 14-28 degrees C, decreasing over 50% when leaf temperature were respectively below 6 degrees C and over 37 degrees C: the low potential photochemical efficiency of 0.71 PSII (Fv/Fm) at Castelporziano during summer, confirmed the state of stress. Transpiration rates remained high with the increase of leaf temperature in summer, in spite of the 46% decrease of stomatal conductance. Nevertheless, this decrease allowed the maintenance of acceptable Pn rates in stressful conditions. The potential productivity of Q. ilex lied on high peaks of activity during periods of lower evaporative demand and a rapid stomatal response to an increase in air temperature and soil water deficit. Although it is difficult to forecast Q. ilex productivity and plant structure, we may hypothesize its future presence in the Mediterranean Basin by the capability of vegetative activity in a wide range of temperatures, the high stomatal control in stressful conditions, the high plasticity index and water use efficiency (WUE). (C) 2000 Elsevier Science B.V. All rights reserved
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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