1,720,973 research outputs found
Phytostabilization of heavy metals: role of plant roots and organic amendments
Full text linkPhytomanagement refers to a group of techniques which use plants to reduce content or toxicity of heavy metals in soils. This thesis focuses on metal phytostabilization, which aims at reducing metal bioavailability in soil. Phytostabilization can occur either in roots or in soils. The first requires the uptake of pollutants and their stable accumulation in root tissues (in-planta phytostabilization), the second insolubilization of metals in soil to prevent plant uptake (ex-planta phytostabilization). For this thesis both these aspects were explored.
In-planta phytostabilization experiments aimed at evaluating the potential accumulation of heavy metals in rapeseed (Brassica napus L. var. oleifera) and the time span within metals are retained in degrading taproots before being released into the soil. The effect of increasing sowing density (22, 44, 63 plant m-2) and genotype selection (CHH normal-sized hybrids, semi-dwarf hybrid, and free-impollination variety) on the dynamics of taproot degradation were evaluated (first year) along with the effect of level of soil metal pollution (second year). The results indicated that degradation of root biomass was relatively fast (-83% within 12 months), but after 18 months still 10% of organic matter was available for metal retention. This indicates that the annual supply of root biomass by cultivation can improve metal retention. Metals are mainly retained in the inner cortex, which also owns a higher rate of cellulose and is more recalcitrant to degradation, thus allowing a greater concentration of pollutants to be observable over time in degrading tissues. Nevertheless, after 18 months metal contents was reduced compared with the initial stock, with concentrations depending on the specific metal. The dynamics of root degradation was independent on genotype choice and plant density, but more vigorous cultivars (CHH hybrids) and elevated plant densities should be preferred if the taproots are meant to stabilize metals, because of the higher biomass production (up to 1700 kg ha-1 in Taurus at 63 plant m-2). High level of soil pollution (Cd, Co, Cu, Zn) slowed down root degradation due to a reduction in the microbial activity. In addition, the consequent high metal bioavailability was associated to significant increases in root metal contents (and concentrations) despite the degradation process progressed. Overall, despite the degradation of roots cannot be stopped, metal stabilization in taproots is feasible in the long-term and it would be more effective in polluted soils where it is of paramount importance to reduce metal mobility and accumulation along the food chain.
Ex-planta phytostabilization trials aimed at evaluating the possible risks of soil metal pollution and plant uptake with waste-derived organic amendments. The effects of organic amendments on soil and plants was greatly affected by chemical characteristics of the amendment and its maturation degree. When the amount of organic carbon added to the soil was the same, better productivity and root growth of forage sorghum were obtained with matured compost which is richer in both N and humic substances. None of the tested amendments, i.e., compost from organic urban wastes, anaerobic digestate from plant biomasses, and pig slurry (separated solid fraction) had hazardous contents of heavy metals. Therefore, when the amendments do not derive from polluted feedstock they do not increase the content of heavy metals in the soil or their concentration in plants. However attention should be paid to metal bioavailability, in the middle term some metals (e.g., Ni, Zn) increased significantly increased their mobility, irrespective of the amendment, although generally higher values were found for the animal-derived amendment (pig slurry) which is richer in dissolved organic matter (DOM). Metal mobility in the amended soils therefore may depend on the presence of soluble species in the amendments themselves and probably on the interaction soil-amendment. Compost appeared as the best amendment among those tested for meeting both the agronomic (productivity) and environmental (carbon stock restoration, metal total and bioavailable contents) demands.
Biochar is also an organic stabilized amendment, but it was not found to have relevant effects in the middle term on plant productivity of barley and bean . The effect of biochar on soil properties (pH increases) was also short lived, while the effects on soil physical properties (aeration and bulk density) and metal partitioning in different soil phases appeared longer-lived. Biochar increased Cu and Zn retention, but also the water-soluble Pb, with differences depending on biochar age and application rate. In fact, the oxidation of biochar aromatic rings changes its chemical properties and the interaction with metals. However, when it is produced from unpolluted feedstock, biochar does not increase soil metal contents or plant uptake, probably because soluble metals are distributed to deeper soil horizons, limiting the accumulation in the rhizosphere. Overall, the real value of biochar lies in the addition of carbon to the soil, rather than in its effect on plants productivity.
On the contrary, when soil amendments are produced from contaminated feedstock, there is a real potential for soil and food-chain contamination. Amendments like biochar and liming agent (e.g. wood ash) concentrate the heavy metals contained in the feedstock material during pyrolysis and incineration respectively. The biochar and wood ash produced from Cu-treated wood in fact were rich in Cu which was available for uptake by plants. The concentration of Cu in sunflower leaves and taproot grown in soil amended with such biochar were greater than those in unpolluted reference soil, while polluted wood-ash severely compromised plant growth (dead of plants) due to the high Cu bioavailability. The increase in soil pH after the addition of amendments was too weak to limit Cu bioavailability when Cu itself was highly concentrated, and this may happen for other metals (e.g., As, Cr) if concentrated in the waste-wood. Above-ground biomass of sunflower was reduced (-40%) in polluted-biochar amended soil, despite plant height was unaffected. Overall, polluted biochar and ash should not be used in agriculture, and alternative uses should be found for polluted wastes
Metodi e fonti per la valutazione sistematica dei documenti
No full textEdizione italiana del volume di Kenneth Whittaker "Systematic evalutation: methods and sources for assessing books
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Effetto dell’insilamento delle vinacce sulle caratteristiche organolettiche della grappa: analisi della frazione carbonilica
No full text- …
