1,720,966 research outputs found
Volatile profile of perennial leaves of seven cultivated species of Ceratozamia (Cycads)
No full textCeratozamia (Zamiaceae) is a genus of New World Cycads, containing more than 20 species distributed in eastern and southern Mexico, with extensions into Central America [1]. Morphology, anatomy, and molecular data allowed resolution of some aspects of species relationships, suggesting phytogeographic hypotheses [2]. Renewed interest in cycads has also resulted in works focused on phytochemical topics [3 and literature therein], however data on the volatile emission profiles lack.
Seven Ceratozamia species belonging to clade “C” [2] and cultivated in a cold greenhouse at the Florence Botanic Garden were investigated: Ceratozamia fuscoviridis D. Moore, Ceratozamia hildae Landry & M. Wilson, Ceratozamia kuesteriana Regel, Ceratozamia latifolia Miq., Ceratozamia longifolia Miq., Ceratozamia mexicana Brongn., Ceratozamia vulgaris J. Schust. Perennial leaves were screened in February, July and September 2011 for the emission of volatile organic compounds (VOCs) by means of headspace solid phase microextraction coupled with gaschromatography and mass spectrometry (HS-SPME-GC/MS); two leaflets per species were sampled from coetaneous leaves, and analysed. In this study we assessed and compared the volatile profiles among species and across sampling periods, with the main objective to collect preliminary information to evaluate the potentiality of VOCs for taxonomic purposes.
The VOC analysis revealed the emission of overall 199 compounds, of which 144 identified. The unknown compounds dominated the volatile profiles, accounting for about 27%, followed by aldehydes, terpenes, alcohols, ketones and esters. The highest number of compounds (115) was found in C. fuscoviridis, the lowest (91) in C. longifolia. In all the examined species, February profiles invariably exhibited the major amount of volatiles in comparison to July and September.
Statistical data processing proved: (i) a low level of diversity among the VOC profiles of the examined species referred to each collection time; (ii) a great variability in the temporal emission patterns of all the species across the three sampling periods.
These evidences revealed the predominance of the environmental components at the study area in affecting the volatile profiles of Ceratozamia species, at the expense of the metabolic resilience related to the different climatic conditions of the native regions. Possible ecological roles of the VOC temporal variation in relation to the plant phenological stages are discussed
Plant species loss and community nestedness after leguminous tree Acacia pycnantha invasion in a Mediterranean ecosystem
No full textInvasions of ecosystems by alien species are one of the major threats to biodiversity. Among alien plant species, members of the family Fabaceae s.l. represent some of the most dangerous and well known global invaders. In Mediterranean ecosystems, many Australian acacias have been found to establish and rapidly spread, often determining severe impacts on understorey vegetation. In the present work, we report a case study of an Acacia pycnantha invasion in a typical Mediterranean matorral (Elba Island, central Mediterranean Sea, Italy). We conducted a survey of understorey plant communities across an invasion gradient from non-invaded to transitional and invaded areas, aiming to quantify the impacts on the understorey assemblage and to investigate the ecological processes involved in the changes in species composition. The understorey plant community was highly affected starting from the intermediate stage of invasion. Species richness, diversity and total cover were all lower in invaded than in non-invaded plots, with a transition generally in the middle. In addition, plant community composition severely changed along the invasion gradient. The species set we recorded showed a nested structure, with the composition of species in the invaded plots representing a subset of the others. According to our findings, A. pycnantha exerted detrimental impacts on the native vegetation, mainly causing a severe species loss in the understorey assemblage and the impoverishment of the invaded ecosystems
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
Inter-population and temporal variation of VOC emission from Mediterranean Helichrysum Mill. (Asteraceae)
No full textMediterranean Helichrysum species are highly diverse with respect to both phenotype and metabolite profile [1].
Volatile organic compounds (VOCs) were recently recognized as valuable tools for studying Helichrysum systematics at population level [2]. In seeking carry on the studies on the phytochemical typification for taxonomic purposes, we examined the diversity and temporal variation of volatile profiles in eight selected Mediterranean populations, included within the H. italicum complex, H. litoreum and H. stoechas. The goals of this study are: (i) to evaluate and compare the differences of volatile profiles across populations and collection time, and (ii) to characterize the intra-population variation over time.
After collection in the wild, plants were cultivated in standard growing conditions at the Florence Botanical Garden, to remove the effects due to the different ecological conditions of the collection sites. The emissions of VOCs from annual leafy shoots were analysed in May, July and September 2012, by means of headspace solid phase microextraction coupled with gas-chromatography and mass spectrometry (HS-SPME-GC/MS).
The VOC analysis revealed the production of overall 417 compounds, with terpenes being the dominant compound class, followed by esters and alcohols.
Statistical data processing, based on a Permutational Multivariate Analysis of Variance and on a subsequent Variance Partitioning Analysis on the relative quantitative data of VOCs, showed a great variability in the volatile profiles across populations (69%, p<0.001), with a weak contribution due to time (5%, p<0.001), whereas the additional variance explained by the interaction term between these two factors is 19% (p<0.001). The volatile profiles of each population were consistent over time, as indicated by the high correlation coefficients (ca 65%), with the exception of only one provenance.
In conclusion, VOC profiles as a whole varied considerably from one population to another, and over time. Conversely, the low diversity of time-to-time emission pattern within each population suggests that the volatile profiles exhibit phytochemical consistency, presumably due to the standardization of the plant growing conditions. These data further enhance the potentiality of VOCs as diacritical characters in discriminating among populations and in solving taxonomic problems
A volatolomic approach for studying plant variability : the case of selected Mediterranean Helichrysum (Asteraceae)
No full textThe species of Helichrysum sect. Stoechadina (Asteraceae) are well-known for their secondary metabolite content and the characteristic aromatic bouquets. In the wild, populations exhibit a wide phenotypic plasticity which makes critical the circumscription of species and infraspecific ranks. Previous investigations on Helichrysum italicum complex focused on a possible phytochemical typification based on hydrodistilled essential oils. Aims of this paper are three-fold: (i) characterizing the volatile profiles of different populations, testing (ii) how these profiles vary across populations and (iii) how the phytochemical diversity may contribute in solving taxonomic problems.
Nine selected Helichrysum populations, included within the H. italicum complex, Helichrysum litoreum and Helichrysum stoechas, were investigated. H. stoechas was chosen as outgroup for validating the method. After collection in the wild, plants were cultivated in standard growing conditions for over one year. Annual leafy shoots were screened in the post-blooming period for the emissions of volatile organic compounds (VOCs) by means of headspace solid phase microextraction coupled with gas chromatography and mass spectrometry (HS-SPME-GC/MS).
The VOC composition analysis revealed the production of overall 386 different compounds, with terpenes being the most represented compound class. Statistical data processing allowed the identification of the indicator compounds that differentiate the single populations, revealing the influence of the geographical provenance area in determining the volatile profiles. These results suggested the potential use of VOCs as valuable diacritical characters in discriminating the Helichrysum populations. In addition, the cross-validation analysis hinted the potentiality of this volatolomic study in the discrimination of the Helichrysum species and subspecies, highlighting a general congruence with the current taxonomic treatment of the genus.
The consistency between this phytochemical approach and the traditional morphometrical analysis in studying the Helichrysum populations supports the validity of the VOC profile in solving taxonomic problems
Soil and plant changing after invasion: the case of Acacia dealbata in a Mediterranean ecosystem
No full textAcacia dealbata Link (Fabaceae) is one of the most invasive species in the Mediterranean ecosystems of Europe, Africa and America, where it has been proved to exert strong effects on soil and plant communities. In Italy A. dealbata has been largely used for ornamental and forestry purpose and is nowadays spreading in several areas. The present study was addressed to evaluate the impacts on soil chemical properties, soil microbial communities and understory plant communities and to assess the relationships among these compartments after the invasion of A. dealbata in a typical Mediterranean shrubland. Towards these aims, a soil and vegetation sampling was performed in Elba Island where A. dealbata is invading the sclerophyllous native vegetation. Three levels of invasion status were differentiated according to the gradient from invaded, to transitional and non-invaded vegetation. Quantitative and qualitative alterations of soil chemical properties and microbial communities (i.e. bacterial and fungal communities) and above-ground understory plant communities were found. In particular, the invaded soils had lower pH values than both the non-invaded and transitional ones. High differences were detected for both the total N and the inorganic fraction (NH4+ and NO3-) contents, which showed the ranking: invaded>transitional>non-invaded soils. TOC and C/N ratio showed respectively higher and lower values in invaded than in non-invaded soils. Total plant covers, species richness and diversity in both the non-invaded and transitional subplots were higher than those in the invaded ones. The contribution of the nitrophilous species was significantly different among the three invasion statuses, with a strong increase going from native to transitional and invaded subplots. All these data confirm that A. dealbata modifies several compartments of the invaded ecosystems, from soil chemical properties to soil and plant microbial communities determining strong changes in the local ecosystem processes
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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