1,720,982 research outputs found
Decreased summer drought affects plant productivity and soil carbon dynamics in a Mediterranean woodland
No full textPrecipitation patterns are expected to change in the Mediterranean region within the next decades, with projected decreases in total rainfall and increases in extreme events. We manipulated precipitation patterns in a Mediterranean woodland, dominated by Arbutus unedo L., to study the effects of changing precipitation regimes on above-ground net primary production (ANPP) and soil C dynamics, specifically plant-derived C input to soil and soil respiration (SR). Experimental plots were exposed to either a 20 % reduction of throughfall or to water addition targeted at maintaining soil water content above a minimum of 10 % v/v. Treatments were compared to control plots which received ambient precipitation. Enhanced soil moisture during summer months highly stimulated annual stem primary production, litter fall, SR and net annual plant-derived C input to soil which on average increased by 130 %, 26 %, 58 % and 220 %, respectively, as compared to the control. In contrast, the 20 % reduction in throughfall (equivalent to 10 % reduction in precipitation) did not significantly change soil moisture at the site, and therefore did not significantly affect ANPP or SR. We conclude that minor changes (around 10 % reduction) in precipitation amount are not likely to significantly affect ANPP or soil C dynamics in Mediterranean woodlands. However, if summer rain increases, C cycling will significantly accelerate but soil C stocks are not likely to be changed in the short-term. More studies involving modelling of long-term C dynamics are needed to predict if the estimated increases in soil C input under wet conditions is going to be sustained and if labile C is being substituted to stable C, with a negative effect on long-term soil C stocks. © Author(s) 2011
Sampling soil-derived CO2 for analysis of isotopic composition: a comparison of different techniques
No full textGoing 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
Litter decomposition and soil CO2 efflux on the Mediterranean island of Pianosa
No full textMediterranean ecosystems are particularly vulnerable to changes in climate and land use forecasted for the near future, with likely perturba- tions of the carbon cycle. The aim of our study was to quantify particular aspects of the carbon cycle in typical Mediterranean ecosystems, in particular (1) the decay rates of litter from common tree and shrub species, (2) the efflux of CO2 from the soil and its relation to soil and litter moisture, and (3) the dynamics of the stable isotope 13 C during litter decomposition.
Field work was conducted on the island Pianosa, which comprises a range of common Mediterranean ecosystem types. Litter decay rates of three selected species (Cistus monspenliensis, Pistacia lentiscus and Juniperus phoenicia) were found to be low with an average of 70 % of initial mass remaining after 2 years of field incubation. Over the same period, all litter types showed only a slight (<10 %) net loss of N. Despite relatively high initial N contents, litter decay rates were comparable to those reported in the literature, suggesting that C and N dynamics are decoupled during litter decomposition.
Over the two years of incubation, 13 C dynamics were not unanimous between the three litter types, with only a slight enrichment in one species. Continuation of this ongoing experiment is likely to resolve the long term effects of decomposition on 13 C enrichment on litter.
Soil CO2 efflux was found to be unusually high (peak rates of over 9 μmol m-2 s-1 ), owing to both high soil water content and soil temperature during an intensive measuring campaign in October 2003. Mean daily fluxes in woodland ecosystems were significantly higher than in either macchia or ex agricultural ecosystems, exceeding the latter about twofold. However, when scaled to the relative surface representation on Pianosa, the highest contribution of daily soil CO2 efflux stems from Macchia type vegetation, followed by abandoned agricultural sites and woodland ecosystems (around 20, 22, and 8.5 t C d-1 , respectively).
With the exception of one site, soil CO2 efflux correlated positi- vely with litter content at different sites across the island. Rather than causing the higher fluxes directly, higher litter contents are likely to indicate higher site productivity rates, resulting in higher CO2 turnover dynamics and hence higher overall soil CO2 efflux rates. Owing to the only small range of soil moisture conditions during the measuring campaign, no dependence of soil CO2 efflux on soil moisture could be detected. However, a range of moisture conditions between sites was noted, indicating the significance of site specific conditions also within the same ecosystem types
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
A new technique to measure soil CO2 efflux at constant CO2 concentration
No full textA new principle for measuring soil CO2 efflux at constant ambient concentration is introduced. The measuring principle relies on the continuous absorption of CO2 within the system to achieve a constant CO2 concentration inside the soil chamber at ambient level, thus balancing the amount of CO2 entering the soil chamber by diffusion from the soil. We report results that show reliable soil CO2 efflux measurements with the new system. The novel measuring principle does not disturb the natural gradient of CO2 within the soil, while allowing for continuous capture of the CO2 released from the soil. It therefore holds great potential for application in simultaneous measurements of soil CO2 efflux and its d 13C, since both variables show sensitivity to a distortion of the soil CO2 profile commonly found in conventional chamber technique
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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