1,721,047 research outputs found
Salinity affects the composition of the aerobic methanotroph community in alkaline lake sediments from the Tibetan Plateau
No full textLakes are widely distributed on the Tibetan Plateau, which plays an important role in natural methane emission. Aerobic methanotrophs in lake sediments reduce the amount of methane released into the atmosphere. However, no study to date has analyzed the methanotroph community composition and their driving factors in sediments of these high-altitude lakes (>4000 m). To provide new insights on this aspect, the abundance and composition in the sediments of six high-altitude alkaline lakes (including both freshwater and saline lakes) on the Tibetan Plateau were studied. The quantitative PCR, terminal restriction fragment length polymorphism and 454- pyrosequencing methods were used to target the pmoA genes. The pmoA gene copies ranged 10? -10? per gram fresh sediment. Type I methanotrophs predominated in Tibetan lake sediments, with Methylobacter and uncultivated type Ib methanotrophs being dominant in freshwater lakes and Methylomicrobium in saline lakes. Combining the pmoA-pyrosequencing data from Tibetan lakes with other published pmoAsequencing data from lake sediments of other regions, a significant salinity and alkalinity effect (P=0.001) was detected, especially salinity, explained ~25% of methanotroph community variability. The main effect was Methylomicrobium being dominant (up to 100%) in saline lakes only. In freshwater lakes, however, methanotroph composition was relatively diverse, including Methylobacter, Methylocystis, and uncultured type Ib clusters. This study provides the first methanotroph data for high-altitude lake sediments (>4000 m) and shows that salinity is a driving factor for the community composition of aerobic methanotrophs
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
Ammonia oxidizers are pioneer microorganisms in the colonization of new acidic volcanic soils from South of Chile
No full textAmmonia oxidation, performed by specialized microorganisms belonging to the Bacteria and Archaea, is the first and most limiting step of soil nitrification. Nitrification has not yet been examined in young volcanic soils. The aim of the present work was to evaluate the abundance and diversity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in acidic volcanic soils (andisols) of different defined ages to determine their relative contribution to nitrification and soil colonization. Soil was collected from three vegetated sites on Llaima Volcano (Chile) recolonized after lava eruptions in 1640, 1751 and 1957. Quantitative polymerase chain reaction, terminal restriction fragment length polymorphism and clone sequence analyses of the amoA gene were performed for the AOA and AOB communities. All soils showed high nitrification potentials, but they were highest in the younger soils. Archaeal amoA genes outnumbered bacterial amoA genes at all sites, and AOA abundances were found to be proportional to the nitrification potentials. Sequencing indicated the presence of AOA related to Nitrososphaera and Nitrosotalea, and AOB related primarily to Nitrosospira and sporadically to Nitrosomonas. The study showed that both AOA and AOB are early colonizers of andisols, but that AOA outnumber AOB and play an important role in nitrification
Different bacterial populations associated with the roots and rhizosphere of rice incorporate plant-derived carbon
No full textMicroorganisms associated with the roots of plants have an important function in plant growth and in soil carbon sequestration. Rice cultivation is the second largest anthropogenic source of atmospheric CH4, which is a significant greenhouse gas. Up to 60% of fixed carbon formed by photosynthesis in plants is transported below ground, much of it as root exudates that are consumed by microorganisms. A stable isotope probing (SIP) approach was used to identify microorganisms using plant carbon in association with the roots and rhizosphere of rice plants. Rice plants grown in Italian paddy soil were labeled with 13CO2 for 10 days. RNA was extracted from root material and rhizosphere soil and subjected to cesium gradient centrifugation followed by 16S rRNA amplicon pyrosequencing to identify microorganisms enriched with 13C. Thirty operational taxonomic units (OTUs) were labeled and mostly corresponded to Proteobacteria (13 OTUs) and Verrucomicrobia (8 OTUs). These OTUs were affiliated with the Alphaproteobacteria, Betaproteobacteria, and Deltaproteobacteria classes of Proteobacteria and the “Spartobacteria” and Opitutae classes of Verrucomicrobia. In general, different bacterial groups were labeled in the root and rhizosphere, reflecting different physicochemical characteristics of these locations. The labeled OTUs in the root compartment corresponded to a greater proportion of the 16S rRNA sequences (∼20%) than did those in the rhizosphere (∼4%), indicating that a proportion of the active microbial community on the roots greater than that in the rhizosphere incorporated plant-derived carbon within the time frame of the experiment
Assimilation of acetate by the putative atmospheric methane oxidizers belonging to the USCα clade
No full textForest soils are a major biological sink for atmospheric methane, yet the identity and physiology of the microorganisms responsible for this process remain unclear. Although members of the upland soil cluster ? (USC?) are assumed to represent methanotrophic bacteria adapted to the oxidation of the trace level of methane in the atmosphere and to be an important sink of this greenhouse gas, so far they have resisted isolation. In particular, the question of whether the atmospheric methane oxidizers are able to obtain all their energy and carbon solely from atmospheric methane still waits to be answered. In this study, we performed stable-isotope probing (SIP) of RNA and DNA to investigate the assimilation of (13) C-methane and (13) C-acetate by USC? in an acidic forest soil. RNA-SIP showed that pmoA mRNA of USC? was not labelled by (13) C of supplemented (13) C methane, although catalysed reporter deposition - fluorescence in situ hybridization (CARD-FISH) targeting pmoA mRNA of USC? detected its expression in the incubated soil. In contrast, incorporation of (13) C-acetate into USC?pmoA mRNA was observed. USC?pmoA genes were not labelled, indicating that they had not grown during the incubation. Our results indicate that the contribution of alternative carbon sources, such as acetate, to the metabolism of the putative atmospheric methane oxidizers in upland forest soils might be substantial
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
Analysis of the microbial communities in soils of different ages following volcanic eruptions
No full textEl primer autor agradece la beca de investigación de la Fundación Alexander von Humboldt y la Sociedad Max Planck, Alemania.The first author acknowledges the research fellowship from the Alexander von Humboldt Foundation and the Max Planck Society, Germany
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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