1,721,073 research outputs found
Effects of ozone and nitrogen deposition in young trees of Hornbeam and Oak. Results from the ECLAIRE experiments in Italy
No full textAn Open-Top Chambers (OTC) experiment with ozone enrichment and increased nitrogen deposition has been performed during two consecutive years (2012 and 2013) in Northern Italy on young trees of Quercus robur and Carpinus betulus. Two hundreds and sixteen saplings of each species were potted and placed in 12 Open-Top Chambers following a split-plot design with 3 randomized blocks and two factors: ozone concentration, the main factor, at 4 different levels (CF-45%, NF, NF+35%, NF+70%), and nitrogen irrigation (NDep), the nested factor, at 2 different levels (tap water for control, tap water +NDep of 70Kg of N*ha*y-1). These treatments were applied for two consecutive growing seasons. In both years stomatal conductance (gs) measurements and CO2 assimilation response curves have been made throughout the season to assess the impacts on physiological and photosynthetical parameters. Half of the saplings was harvested at the end of 2012 season, while the remaining half was harvested at the end of 2013, in order to estimate the effects of both stresses, alone and in combination, on the total biomass production and on the root/shoot partition of the plants.
After two years of treatments, a general positive effect of nitrogen deposition on biomass production was found in both species, as it could be easily expected. This biomass increase was particularly intense in C. betulus (+76% of the total biomass, + 65% of roots biomass).
Q. robur showed a greater response to ozone than C. betulus in the control Ndep conditions. Oak plants showed a 10% and 18% of reduction of the total and root biomass in NF+70% treatment. This response was also found in the plants subjected increased to nitrogen deposition (-15% for total biomass, -16% for roots biomass). Hornbeam seemed stimulated by O3 when no nitrogen was added (+5% of total biomass). However, NDep treatment made hornbeam more susceptible to ozone, which caused a 30% biomass decrease in both shoots and roots.Looking at gs as a possible driver of the plants’ response to ozone, we found that ozone lead to a 21% decrease of gs in oak plants when the had a total biomass reduction of 10%. This response is confirmed in NDep treatment (-18% in gs, -15% in total biomass). Thus, oak seemed to be more vulnerable to gs limitation because of the consequent reduction of CO2 assimilation.In hornbeam, without nitrogen addition, ozone caused a slight reduction on gs leading to a decrease of stomatal dose and a small increase in total biomass (+5%).
On the contrary, nitrogen deposition caused a significant increase of gs (+23%) that lead to an increased ozone uptake, thus suggesting an overwhelming of the detoxifying defence (-30% in total biomass).Stomatal conductance, thus, reveals to be a key driver of the plant’s response to ozone, but the final manifestation of the effect seems to be modulated by the detoxifying capacity of the plants.
The general decrease of gs in both species caused by ozone (also found in 2012 measurements), suggests the need to include an f(O3) modifying function in the stomatal conductance models which will be defined for these two species. Some of biomass responses are partially in disagreement with the results of the first year, likely for the presence of a carry over effect. This fact highlights the importance of performing long-term experiments (more than 1 year) for the investigation on ozone and nitrogen effects on biomass
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Yield response of some italian and spanish cultivars of durum wheat to elevated ozone: a varietal screening
No full textDurum wheat is the main wheat species grown in Southern Europe countries. Hence, the evaluation of the response of the main cultivars of durum wheat to tropospheric ozone is a priority for Southern Europe. The present work investigated the O3 effects on five cultivars of durum wheat, three of them from Italy (Colombo, Sculptur, Faraon) and two from Spain (Gallareta and Vitron) in terms of yield and related physiological drivers.
The experiment was performed in the open-top chambers (OTC) facility of C.R.IN.E.S at Curno, Italy, from 09th March to 15th June 2013. Each cv was sown in 12 pots (three plants per pot) and pots were randomly assigned to 4 OTC (three pots per OTC for each cv), two of them supplied with charcoal filtered air (-50% of ambient air ozone = CF) and two with ozone enriched air (+50% of ambient air ozone = EN). During the experiment the ozonated plants were exposed to a daylight AOT40 value of 11.561 ppm•h, well above the UN/ECE critical level of 3 ppmh, while the control (CF) plants experienced an exposure of 0.432 ppm•h.
Periodical measurements of stomatal conductance, chlorophyll-a fluorescence and growth were performed during the growing season. Furthermore, macroscopic (chlorotic/necrotic spots) and microscopic (cell death and H2O2 deposits in mesophyll tissue) symptoms development were followed on the flag leaves. At the end of the season plants were harvested and the stems and the ears of each plant were separately dried and weighted. Then the grain yield was assessed per each OTC as total grain weight and hectoliter weight.
The Italian cv Sculptur, the most productive one without ozone, together with the cv Colombo resulted the most ozone sensitive cvs, with a grain yield decrease of 16% (p<0.05) and 10% (ns) respectively in the EN treatment. Nevertheless very small differences were observed in the hectoliter weight between the two ozone treatments. The remaining cvs did not show any negative effect of ozone but rather a slight yield stimulation (between 1 and 5%, ns). The Spanish Gallareta resulted the best performing cv when both CF and EN yield are considered.
Ozone affected the earing and the plants growth: the number of ears was quite uniformly reduced by ozone, with a remarkable low for Sculptur, and the losses of the aboveground biomass confirm the ozone sensitivity of Sculpur and Colombo (-20% and -25% respectively, both p<0.01).
The stomatal conductance was greatly decreased by ozone in all cvs (between 11% and 37%, p<0.01), but it is notable that the most sensitive cvs showed the highest gs values, even under the ozone treatment, which implies a highest ozone dose. This would confirm that the stomatal dose is an important driver of the plants’ response to this pollutant.
On the contrary the overall performance of the photosynthesis (PI) - assessed by the OJIP test on the chlorophyll fluorescence measurements – was not affected by ozone. Thus, the observed reduction of productivity in the sensitive cvs is not to be ascribed to a damage of the photosystyems but rather to a dissipation of the available energy for the metabolic defense against the oxidative stress.
Finally, the observation of the the Sculpure cv behaviour suggests that the breeding strategy of selecting a greater gs to increase the yield may not be appropriate under increasing ozone conditions
Stomatal uptake and non-stomatal ozone removal by a mixed Oak-Hornbeam mature forest in the Po valley: results of the ECLAIRE long-term campaign
No full textIn the framework of the ÉCLAIRE Project of the 7th EU framework programme a joint field campaign and a following long-term one had been conducted at an Oak-Hornbeam mixed mature forest in the Po Valley (Bosco Fontana, Mantova, Italy). Inside the forest, a 42 m tall micrometeorological tower was installed to measure the mass (O3, CO2, H2O) and energy exchange between the ecosystem and the atmosphere. The focus of this work will be on the ozone flux measurements which started in June 2012 and are currently running.
The ecosystem behaved as a relevant sink for tropospheric ozone, both in summer and in winter, with an average monthly ozone removal of 5.8 kg ha-1 and a total annual deposition of more than 70 kg ha-1. The stomatal flux, estimated by deriving the bulk stomatal resistance through the inversion of the Monteith equation. The maximum stomatal fraction was observed in July 2013 (55%) and the minimum in October 2012 (13%). A strong interannual variability about the stomatal deposition between summer 2012 and 2013 was observed. The phytotoxic ozone doses taken up by the plants were respectively 13.5 mmol m-2 in 2012 and 29 mmol m-2 in 2013.
The non-stomatal deposition, obtained as a residual between the total and the stomatal ozone fluxes, was investigated too. In the joint field campaign Neimitz et al. (2013) found that half of the non-stomatal deposition, was due to NO soil emission, which were on average above 100 mg N m-2 s-1. A minor part of the non-stomatal fluxes (6%) was attributed to isoprene reactions with ozone. A large part of the non-stomatal deposition (44%) was not explained. An investigation on this part, with particular attention on the deposition on non-transpiring surfaces, will be showed.
Additional measurements of O3, NO and NO2 concentrations along the tower profile, allowed to estimate the ozone storage inside the trunk space. The ozone storage can be seen as a part of the deposition flux which is temporarily stored into the trunk space. Taking it into account, the daily course of the non-stomatal deposition significantly changed, with important consequences for non-stomatal interpretation and for proper modelling of the non-stomatal processes.
An estimation of the ozone impact on the whole ecosystem was assessed by looking at the departure from the carbon dioxide balance closure. First results of CO2 exchange seem to indicate a net emission of CO2 from the ecosystem, as it should not be expected from a healthy mature forest ecosystem where, typically, the carbon balance is zero. Again, a general limitation of the net carbon uptake has been observed at high ozone stomatal fluxes.
Finally, the great differences observed in the two years highlight the need for long time series of flux measurements. Moreover, this kind of studies will help in raising the awareness of the policy makers on the ecosystem services offered by the vegetal ecosystems
Photosynthetic performance of Quercus ilex L. under long-term ozone exposure probed by carboxylation efficiency, maximum apparent quantum yield and modulated 820 nm reflection
No full textAssessing ozone (O3) effects on photosynthetic machinery is a key issue to understand how the oxidative stress influences vegetation functionality and the ecosystem services provided (Manes et al., 2012). Moreover, data about the RuBisco and photosystem functionality measured during long term experiments could be important to improve the accuracy of ozone flux models to be use for risks assessment (Fares et al., 2012). Trends towards tolerance to O3 have been studied for Mediterranean tree species and contrasting results were obtained over a large number of experiments, probably due to different levels of O3 exposure and growth conditions. Moreover, only few experiment assessed the O3 effects on evergreen species in terms of dynamic response of CO2 assimilation to varying conditions of temperature and photosynthetic photon flux density (Mereu et al., 2011) and, to the best of our knowledge, no data is available about fluorescence of photosystems I (PSI), that plays a key role in response to oxidative stress. In this experiment, we have assessed long-term effects of O3 exposure on Quercus ilex, an evergreen species with great ecological relevance in Mediterranean Basin for its wide natural distribution, as well as widespread use in urban context. Two-years-old seedlings were continuously exposed for 5 months in open-top chambers facility at the Centre for Research on Effects of Pollutants on Ecosystems, in Curno, to three O3 treatments: charcoal filtered air (F, - 41% of ambient air O3), and non-filtered air supplemented with + 35% (NF+) and +71% ppb O3 (NF++) of ambient air O3. Interestingly, it was found that after 40 days of starting experiment, an early response to O3 leads to an increase in leaf dark respiration and photorespiration. Fluorescence parameters were also affected, and in particular the PSI functionality was involved in the first phase of oxidative stress response
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
