1,721,193 research outputs found
Accumulation of nutrients and heavy metals in Phragmites australis (Cav.) Trin. ex Steudel and Bolboschoenus maritimus (L.) Palla in a constructed wetland of the Venice lagoon watershed
No full textA recently constructed wetland, located in the Venice lagoon watershed, was monitored to investigate growth dynamics, nutrient and heavy metal shoot accumulation of the two dominating macrophytes: Phragmites australis and Bolboschoenus maritimus. Investigations were conducted over a vegetative season at three locations with different distance to the inlet point to assess effects on vegetation. The distance from the inlet did not affect either shoot biomass or nutrients (N, P, K and Na) and heavy metals (Cr, Ni, Cu and Zn) shoot content. With the exception of Na, nutrient and heavy metal concentrations were higher in shoots of P. australis than in B. maritimus. Heavy metal concentration in the incoming water and in the soil was not correlated to the plant content of either species. Shoot heavy metal concentrations were similar to those reported in the current literature, but accumulation generally increased towards the end of the growing season
Herbarium specimens as a source of DNA for AFLP fingerprinting of Phragmites (Poaceae): Possibilities and limitations
No full textHerbarium collections are a valuable source of genetic information. Even though the DNA obtained from the specimens is often highly fragmented and present in small quantities, it has been successfully used particularly for DNA sequencing and microsatellite analysis. The present study shows that the quality is often sufficient for use also for AFLPs. With this technique, a considerable number of DNA fragments with unknown sequence from the entire genome of the plant are amplified, often with the purpose of phylogeographic studies or analyses of interrelationships of closely related species. In order to avoid the effects of potential artefacts resulting from DNA degradation, such as "false polymorphisms", it is suggested that fresh samples should always be included for comparison, and that AFLP chromatograms based on herbarium specimens should be included in analyses only when they contain AFLP fragments monomorphic among the fresh samples, and when signal quality is comparable to that of fresh samples. © 2008 Springer-Verlag
Osmotic and ionic effects of NaCl and Na2SO4 salinity on Phragmites australis
No full textOsmotic and ion-specific effects of NaCl and Na(2)SO(4) on Phragmites australis (Cav.) Trin ex. Steud. were investigated in a laboratory experiment by examining effects of iso-osmotic solutions of NaCl and Na(2)SO(4) on growth, osmolality of cell sap, proline content, elemental composition and gas exchange. Plants were supplied with a control standard nutrient solution (Psi = -0.09 MPa) or solutions of NaCl or Na(2)SO(4) at water potentials of -0.50, -1.09 or -1.74 MPa. Salt treatments increased root concentrations of Na and S or Cl, whereas P. australis had efficient mechanisms for exclusion of Na and S and partly Cl ions from the leaves. Incomplete exclusion of Cl from the leaves may affect aboveground biomass production, which was significantly more reduced by NaCl than Na(2)SO(4). Stomatal conductance was negatively influenced by decreasing water potentials caused by NaCl or Na(2)SO(4), implying that a non-significant photosynthetic depression observed in plants grown at -1.74 MPa was mainly due to osmotically induced stomatal closure. This was supported by decreasing internal CO(2) concentrations. Saline conditions increased the intrinsic water use efficiency and did not alter photosynthetic parameters derived from light response curves, supporting the assumption of a well-functioning CO(2) utilization in salt stressed plants. The leaf proline concentration increased equally in NaCl and Na(2)SO(4)-treated plants, and may play an important role as a compatible organic solute. P. australis possesses a range of mechanisms conferring tolerance to both NaCl and Na(2)SO(4) stress and except in terms of growth the phytotoxicity of NaCl and Na(2)SO(4) are comparable
Interactive effects of elevated temperature and CO2 on two phylogeographically distinct clones of common reed (Phragmites australis)
Full text linkThe aboveground growth, physiological and biochemical parameters of two clones of the cosmopolitan wetland grass Phragmites australis, grown at four treatment combinations of temperature and O2, were investigated to elucidate whether their climate response differed due to inherent differences in their ecological adaptation. The two phylogeographically distinct P. australis clones (DK clone, European genetic background; ALG clone, Mediterranean genetic background) were grown for 151 days in phytotrons at 19/12 8C (day/night temperature) and 390 ppm CO2, and at elevated temperature (+5 8C) and CO2 (700 ppm) with treatment factors alone or in combination.
The ALG clone had 2–4 times higher aboveground biomass, higher light-saturated rates of photosynthesis (Pmax), maximum electron transport rates (ETRmax) and Rubisco activity, and higher photosynthetic nitrogen-use efficiency than the DK clone. The DK clone, however, produced more shoots, leaves and sideshoots, and had 9–51 % higher specific leaf area and 15–39 % higher leaf nitrogen concentration than the ALG clone. Although elevated atmospheric CO2 alone barely affected the aboveground growth of the two P. australis clones, simultaneously elevated temperature and CO2 stimulated growth and aboveground biomass. Overall, elevated CO2 stimulated photosynthesis, but the clones responded differently to a concomitant increase in CO2 and temperature, depending on the phylogeographic background of the plant. The DK clone showed overall stronger responses, and can be considered the more plastic of the two clones with respect to CO2 and
temperature. Thus, the DK clone may be better adapted to climate change than the ALG clone, at least in the short term
Genetic diversity patterns in Phragmites australis at the population, regional and continental scales
No full textGenetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool. Nearly all populations studied are polyclonal and little correlation was found between genetic diversity and size, age and degree of human impact on the wetlands. One large (86 ha) monoclonal stand occurred in an old wetland with rather stable environmental conditions over a long time period, whereas polyclonal stands were younger and characterized by disturbance. On the interpopulation level it was not possible to differentiate between Po Plain populations and the Romanian population, indicating that a very extensive gene pool exists in Europe, to which both Po Plain and Romanian populations belong. There is however a certain degree of genetic structure among the populations that is not correlated with geographic distance, but is most likely related to P. australis colonization dynamics. A significant "stepwise" increase in average genetic distances was observed between clones >500 and >1500 km distant suggesting some kind of genetic pattern on a very large scale. Based on these results, P. australis populations in Europe could be considered members of a single meta-population. © 2007 Elsevier 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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