1,720,958 research outputs found
Photosynthesis in chlorolichens: the influence of the habitat light regime
No full textThe hypothesis that CO2 gas exchange and
chlorophyll a fluorescence (ChlaF) of lichens vary
according to the light regimes of their original habitat, as
observed in vascular plants, was tested by analysing the
photosynthetic performance of 12 populations of seven
dorsoventral, foliose lichens collected from open, southexposed
rocks to densely shaded forests. Light response
curves were induced at optimum thallus water content and
ChlaF emission curves at the species-specific photon flux at
which the quantum yield of CO2 assimilation is the highest
and is saturating the photosynthetic process. Photosynthetic
pigments were quantified in crude extracts. The results
confirm that the maximum rate of gross photosynthesis is
correlated with the chlorophyll content of lichens, which is
influenced by light as well as by nitrogen availability.
Like leaves, shade tolerant lichens emit more ChlaF than
sun-loving ones, whereas the photosynthetic quantum
conversion is higher in the latter
Effects of Mediterranean summer conditions on chlorophyll a fluorescence emission in the epiphytic lichen Flavoparmelia soredians: a field study.
No full textRecent hypotheses suppose that dry lichens emit a faint chlorophyll a fluorescence because of a “long-wavelength quencher” embedded in the antenna complex that protects photosystem II (PSII) from photodamage. To verify in the field the PSII re-activation promptness induced by water availability, chlorophyll a fluorescence was measured on the epiphytic lichen Flavoparmelia soredians after two months without rainfall events in a Mediterranean cork oak wood (Bosco Santo Pietro, Sicily, Italy). Measurements were carried out at dawn and sunset on north- and south-exposed populations under different regimes of hydration and dark-adaptation. The results show that prolonged hydration increases the photochemical conveying of energy to PSII and decreases the non-photochemical energy dissipation that otherwise might occur in the antenna complex of the lichen photobionts. A slight decrease in PSII efficiency caused by photoinhibition was observed in thalli exposed to ambient light (up to 600 μmol photons m-2 s-1) only when kept fully hydrated. The results are discussed on the basis of our knowledge on the ecology of the species, that is a representative component of Mediterranean epiphytic lichen communities
Ambient NOx influences chlorophyll a fluorescence in transplanted Flavoparmelia caperata lichen.
No full textTransplants of Flavoparmelia caperata (L.) Hale were used to test possible relationships between chlorophyll a fluorescence (CaF) and ambient atmospheric conditions (temperature, precipitation, SO2 and NOx levels). Portions of the same thalli collected in a pristine site (A) of the Trieste Karst were exposed at that site, as the control, and in four other sites (B E) in NE Italy, near to pollution monitoring stations. These sites had been selected in order to provide similar two by two climatic conditions (sites B,C: more humid; D,E: drier) and air pollution load (sites B,D: low; C,E: high). Before exposure and after 43 and 90 days of exposure, CaF measurements were carried out in the laboratory under controlled conditions. A classification of meteorological and pollution parameters recorded during exposure substantially confirmed the differences between site couplets. After 90 days, samples from sites A (control) and B (with very low pollution load) showed only slightly reduced NPQ, qN, Fo, and Fm values. Samples from site D, with medium air pollution load, and sites C,E, with high air pollution loads, showed proportionally greater variation for most of the CaF parameters. A highly significant correlation was found between NPQ, qN, Fm, and NOx pollution but not with SO2 or O3. Effects of NOx on lichens and possible action mechanisms are discussed. The results strongly suggest that CaF measurements of lichen transplants can be a valid tool in biomonitoring studies
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
Effetti degli NOx sulla fisiologia dei licheni foliosi epifiti
Full text link2007/2008L’obiettivo della ricerca è stato individuare i possibili effetti degli NOx, inquinanti aerodiffusi foto-ossidanti, sui licheni foliosi epifiti. Il lavoro è stato svolto con un particolare riguardo nell’individuare le modificazioni indotte a carico del processo fotosintetico del fotobionte lichenico attraverso metodi fluorimetrici. Le ricerche condotte hanno approfondito inizialmente alcuni aspetti metodologici, individuando, ad esempio, le variabili ambientali che influenzano maggiormente la capacità e l’efficienza fotosintetica di questi organismi. Successivamente, è stata disegnata una articolata sperimentazione, condotta mediante trapianti in siti urbani inquinati e non, che ha permesso di verificare gli effetti degli inquinanti aerodiffusi a concentrazioni ambientali in presenza di altri, naturali, fonti di disturbo. Questo lavoro dimostra, attraverso misure fisiologiche, che l’arido microclima urbano può essere un fattore limitante la fisiologia dei licheni e che la loro tolleranza agli NOx dipende strettamente dalla loro ecologia.XXI Ciclo198
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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