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Integrated approach on the rhizosphere response to Nickel in a facultative hyperaccumulator species
No full textThe contamination of metals like Nickel (Ni) in the soil represents a serious threat worldwide. To
counteract this phenomenon, hyperaccumulator plant species, able to remove metal from soil and store it at high concentration in shoots, are employed for metal phytoremediation purposes. Native microbial communities occurring in the rhizosphere of hyperaccumulators often promote plant growth and metal uptake.
So far, each abiotic and biotic rhizospheric components (soil, root system and microbiota) have
been used without considering the reciprocal interactions and the responses to Ni stress as a whole.
The present study aims to develop for the first time an innovative and multidisciplinary approach to examine the rhizosphere of Ni-hyperaccumulators as a holistic model, promoting the plant development and the Ni uptake. This integrated system is feasible owing to the collaboration with the Laboratory of Micology and the Laboratory of Microbiology of Department of Earth, Environmental and Life Sciences (DISTAV), University of Genoa.
Among metalliferous soils, specific attention was given to serpentinitic soil which display
extremely hostile conditions (nutrient shortage and concentration of metals - e.g., Ni - highly toxic) for most plants except for some hyperaccumulator species.
Early response to Ni in plant development was assessed with micro- and mesocosm germination
tests under Ni stress in the Ni-hyperaccumulator species Alyssoides utriculata (L.) Medik, Noccaea caerulescens (J. Presl & C. Presl) F. K. Mey. and Odontarrhena bertolonii (Desv.) L. Cecchi & Selvi and on the related non-accumulator species Alyssum montanum L. and Thlaspi arvense L., used for comparison. Afterwards, the response to increasing Ni concentrations in terms of root surface area, root and shoot biomass and photosynthetic efficiency was evaluated.
Subsequently, A. utriculata was selected as a good candidate to study rhizospheric components
because of its Ni-facultative hyperaccumulation traits and its ability to thrive in harsh metalliferous soils. Related rhizosphere and bare soil samples were collected from serpentine and non-serpentine sites. Plant and soil samples were processed and analysed with specific attention to isolation and identification of culturable microbiota, then selected for their Ni-tolerance and Plant Growth Promoting (PGP) traits. Later, most performing Ni tolerant bacterial and fungal strains were tested by means of co-growth methods to estimate their reciprocal behaviour in a mixed culture to be used as inoculum in the rhizosphere of A. utriculata.
Results demonstrate that increasing Ni concentrations can induce marked inhibition of germination in hyperaccumulator species, despite their accumulation ability. However, hyperaccumulator species exhibit a positive response in terms of root surface area, biomass and photosynthetic efficiency, compared to non-hyperaccumulator species in which there is a dose-response effect by Ni, except for T. arvense in pot test.
In particular, A utriculata reveals an increased aboveground biomass and sample vitality in pot test, suggesting an adaptation to harsh environmental conditions.
Microbiota isolates are more abundant in non-serpentinitic and rhizospheric soil, without selectivity between microorganisms and Ni.
Some bacterial and fungal strains (Pseudomonas sp. SERP1, Streptomyces sp. SERP4 and
Penicillium ochrochloron Biourge Serp03S, Trichoderma harzianum Rifai Serp05S respectively)
reveal high Ni tolerance (up to 20 nM) and PGP traits. In particular SERP1 and Serp03S display a
mutual synergism in co-growth methods and they could be promising candidates as natural
chelators in the rhizosphere of A. utriculata, to enhance plant development and Ni uptake.
This research represents the first step of integrated plant-microbiota tool, in the perspective to
improve Ni uptake from polluted soil, using native Ni-hyperaccumulator species and associated
rhizobiota, although further investigations are required to ascertain the efficiency of the field
application
A Mini-Review on the Co-growth and Interactions Among Microorganisms (Fungi and Bacteria) From Rhizosphere of Metal-Hyperaccumulators
Full text linkThe co-growth and synergistic interactions among fungi and bacteria from the rhizosphere of plants able to hyper accumulate potentially toxic metals (PTMs) are largely unexplored. Fungi and bacteria contribute in an essential way to soil biogeochemical cycles mediating the nutrition, growth development, and health of associated plants at the rhizosphere level. Microbial consortia improve the formation of soil aggregates and soil fertility, producing organic acids and siderophores that increase solubility, mobilization, and consequently the accumulation of nutrients and metals from the rhizosphere. These microorganism consortia can both mitigate the soil conditions promoting plant colonization and increase the performance of hyperaccumulator plants. Indeed, microfungi and bacteria from metalliferous soils or contaminated matrices are commonly metal-tolerant and can play a key role for plants in the phytoextraction or phytostabilization of metals. However, few works deepen the effects of the inoculation of microfungal and bacterial consortia in the rhizosphere of metallophytes and their synergistic activity. This mini-review aimed to collect and report the data regarding the role of microbial consortia and their potentialities known to date. Moreover, our new data had shown an active fungal-bacteria consortium in the rhizosphere of the hyperaccumulator plant Alyssoides utriculata
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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