1,720,962 research outputs found
Elevated CO<sub>2</sub>, water relations and biophysics of leaf extension in four chalk grassland herbs
No full textDiurnal measurements of leaf or leaflet, extension, water relations and cell wall extensibility (φ) were made on young growing leaves of four chalk downland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vulneraria L. and Plantago media L.) growing in controlled environment cabinets and exposed to either ambient or elevated CO2. This study revealed differences in that effect of CO2 and the-control of leaf growth between the four species. Leaf extension rate (LER) increased significantly at night (average over 8 h) in elevated CO2 for S. minor A. vulneraria and P. Media with a significant increase over the first 4h of darkness for S. minor, L, corniculatus and P. media, whilst for S. minor and P. media average day-time LER (over 16 h) also increased significantly in elevated CO2, as compared with ambient CO2. Water potential (Ψ), solute potential (Ψs), turgor pressure (P), yield turgor (Y) and the effective turgor for growth (Pe) were measured using psychrometers. Solute potentials of S. minor, A. vulneraria and P. media decreased significantly following exposure to elevated CO2 with a Significant reduction in Ψs, during the day in A. Vulneraria. Turgor pressure increased significantly in elevated CO2 as compared with ambient CO2 in A. vulneraria but there was no effect of elevated CO2 on P in the other species. No effects of CO2 on Ψ; Y or Pe were observed. Leaf cell wall extensibility (φ) increased significantly in leaves of S. minor, L. corniculatus and P. media exposed to elevated CO2, whereas in A. vulneraria, there was no effect of CO2 on extensibility.These results suggest that the mechanism by which elevated CO2 promotes leaf growth differs between species arises in S. minor, L. corniculatus, and P. media, CO2 through an influence on cell wall properties, whist in A. vulneraria higher values of P explain that increased leaf growth in elevated CO2 for this species
Contrasting effects of elevated CO2 on the root and shoot growth of four native herbs commonly found in chalk grassland
No full textThe aim of this study was to investigate the impact of ambient (345 ?l l?1) and elevated (590 ?l l?1) CO2on the root and shoot growth of four native chalk grassland herbs: Sanguisorba minor Scop, (salad burnet), Lotus carniculatus L. (birdsfoot trefoil), Anthyllis vulneraria L. (kidney vetch) and Plantago media L. (hoary plantain).Elevated CO2 had contrasting effects on both shoot and root growth of the four species studied. Both leaf expansion and production were stimulated by elevated CO2 for S. minor, L. corniculatus and P. media, whilst for A. vulneraria, only leaflet shape appeared to be altered by elevated CO2, with the production of broader leaflets, compared with those produced in ambient CO2. After 100 d shoot biomass was enhanced in elevated CO2 for S. minor and L. corniculatus, whilst there was no effect of elevated CO2 on shoot biomass for A. vulneraria or P. media. Contrasting effects of CO2 were also apparent for measurements of specific leaf area (SLA), which increased for L. corniculatus, decreased for A. vulneraria and remained unaltered for S. minor and P. media in elevated compared with ambient CO2.Elevated CO2 also had contrasting effects on both the growth and morphology of roots. The accumulation of root biomass was stimulated following exposure to elevated CO2 for S. minor and L. corniculatus whilst there was no effect on root biomass for A. vulneraria or P. media. Root length was measured on three occasions during the 100 d and revealed that exposure to elevated CO2 promoted root extension in S. minor, L. corniculatus and P. media, but not in A. vulneraria. Specific root length (SRL, length per unit dry weight) was increased in elevated CO2 for one species, P. media, whilst the root to shoot ratio of all four species remained unchanged by CO2.These results show that four native herbs differ in their response to CO2, suggesting that the structure of this plant community may be altered in the future
Contrasting effects of elevated CO2 and water deficit on two native herbs
No full textThis study investigated the effects of carbon dioxide (CO)2 enrichment and soil water deficit on the water use efficiency (WUE) and growth of Sanguisorba minor Scop, (salad burnet I and Anthyllis vulneraria L. (kidney vetch), growing in controlled environments. Instantaneous WL E (IWUE) increased in both species in elevated CO2, with a higher average increase in unwatered (UW) A. vulneraria over the drying cycle. Total plant WUE of A. vulneraria increased in elevated CO, and under water deficit: the UW plants in elevated CO., had higher WUE and reduced water loss. By contrast, thee was only an effect of water supply on S. minor: total plant WUE increased and water loss decreased in the UV plants in both CO2, treatments. Total apparent root length (ARL) of both species increased with CO2, enrichment and in UW S. minor total ARL was increased. By contrast, for A. vulneraria, total ARL of UV plants increased in ambient CO2, but decreased in elevated CO2 as compared with well-watered (WW) plants. Shoot dry weight (SDW) and root dry weight increased in both species (WW and UW) with CO2. enrichment. For UW S. minor, SDW decreased relative to WW plants in both CO2 treatments. By contrast, ANOVA showed no significant effect of water supply on SDW of A. vulneraria. Leafier length increased in both species in elevated CO2, and decreased following drought. Cell wall tensiometric extensibility (%P) increased in expanding leaves of S. minor in elevated CO., and for both species %P decreased in the UW plants as compared with those WW. Leaf water potential (f) of both species was lower in growing leaves of WAV plants in elevated CO2 Water deficit reduced the ? of growing leaves in both CO2, treatments. The different responses of these species suggest that in a drier, enriched CO2, environment survival in a community might depend on their ability to maintain growth at the same time as conserving water
Elucidating genomic regions determining enhanced leaf growth and delayed senescence in elevated carbon dioxide
No full textLimited information is available on the genetic variation and control for plant growth response to elevated CO2 (e[CO2]). Such information is necessary to understand plant adaptation and evolution in future rising CO2. Here, quantitative trait loci (QTL) for leaf growth, development, quality and leaf senescence were determined in a tree pedigree – an F2 hybrid of Populus trichocarpa T. & G and Populus deltoides Marsh, following season-long exposure to either current day ambient carbon dioxide (a[CO2]) or e[CO2] at 600 µL L1. Leaf growth and development differed between the grandparents such that P. trichocarpa showed greater response to e[CO2]. In the F2 generation, leaf development and quality traits including leaf area, leaf shape, epidermal cell area, and stomatal number, specific leaf area (SLA), and the phenology trait, canopy senescence index, were sensitive to e[CO2]. Sixty-nine QTL were mapped for the 19 traits of plants in a[CO2] while 60 QTL were mapped for plants in e[CO2]. The results suggest that although many QTL mapped to common positions in a[CO2] and e[CO2], confirming their importance in determining growth, there was also differential genetic control for a number of traits including leaf senescence. Candidate genes were shown to collocate to regions where response QTL mapped. This study is the first to identify candidate genes that may be important in determining plant adaptation to future high-CO2 world.<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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