1,720,970 research outputs found
Isoprenoid emissions, photosynthesis and mesophyll diffusion conductance in response to blue light
No full textThe effects of blue light (BL) on leaf gas exchange of Populus×canadensis, a strong isoprene emitter, and Quercus ilex and Citrus reticulata, two monoterpene emitters with respectively small and large storage pools for monoterpenes, were studied. Leaves were initially exposed to a saturating photosynthetic photon flux density (PPFD) of white light (WL), which was then progressively reduced to perform WL-response curves. Leaves acclimated to saturating WL were then quickly exposed to equivalent BL levels to perform BL-response curves. Blue light did not significantly affect photosynthetic parameters in the light-limited portion of the PPFD-response curves in both P.×canadensis and Q. ilex. Whereas photosynthesis (A), stomatal conductance (gs), and mesophyll conductance (gm) were significantly decreased at high PPFDs of BL. A was similarly inhibited by BL in C. reticulata, but there was no significant effect of light quality on gs. Overall these results show that the negative effect of BL on photosynthesis is widespread in tree species with different leaf characteristics, and that this involves coordinated reductions in gs and gm. BL negatively affected isoprene emission and, to a lesser extent monoterpene emissions, in concert with photosynthetic inhibition. Interesting, both isoprene and monoterpene emissions were shown to be inversely dependent upon intercellular [CO2]. These results indicate that a change in light spectral quality, which can vary during the day, between days and within seasons, can alter photosynthesis and isoprenoid emissions, depending on the PPFD intensity. Such effects should be strongly considered in photosynthesis and volatile isoprenoid emission models. © 2013 Elsevier B.V
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
Emission of constitutive isoprene, induced monoterpenes, and other volatiles under high temperatures in Eucalyptus camaldulensis: A 13C labelling study
No full textEucalypts are major emitters of biogenic volatile organic compounds (BVOCs), especially volatile isoprenoids. Emissions and incorporation of 13C in BVOCs were measured in Eucalyptus camaldulensis branches exposed to rapid heat stress or progressive temperature increases, in order to detect both metabolic processes and their dynamics. Isoprene emission increased and photosynthesis decreased with temperatures rising from 30°C to 45°C, and an increasing percentage of unlabelled carbon was incorporated into isoprene in heat-stressed leaves. Intramolecular labelling was also incomplete in isoprene emitted by heat-stressed leaves, suggesting increasing contribution of respiratory (and possibly also photorespiratory) carbon. At temperature above 45°C, a drop of isoprene emission was mirrored by the appearance of unlabelled monoterpenes, green leaf volatiles, methanol, and ethanol, indicating that the emission of stored volatiles was mainly induced by cellular damage. Emission of partially labelled acetaldehyde was also observed at very high temperatures, suggesting a double source of carbon, with a large unlabelled component likely transported from roots and associated to the surge of transpiration at very high temperatures. Eucalypt plantations cover large areas worldwide, and our findings may dramatically change forecast and modelling of future BVOC emissions at planetary level, especially considering climate warming and frequent heat waves
The interaction of biotic and abiotic factors at multiple spatial scales affects the variability of CO2 fluxes in polar environments
No full textClimate change may turn Arctic biomes from carbon sinks into sources and vice versa, depending on the balance between gross ecosystemphotosynthesis, ecosystem respiration (ER) and the resulting net ecosystem Exchange (NEE). Photosynthetic capacity is species specific, and thus, it is important to quantify the contribution of different target plant species to NEE and ER. At Ny A ° lesund (Svalbard archipelago, Norway), we selected different Arctic tundra plant species and measured CO2 fluxes at plot scale and photosynthetic capacity at leaf scale. We aimed to analyze trends in CO2 fluxes during the transition seasons (beginning vs. end of the growing season) and assess which abiotic (soil temperature, soil moisture, PAR) and biotic (plot type, phenology, LAI, photosynthetic capacity) factors influenced CO2 emissions. NEE and ER differed between vegetation communities. All communities acted as CO2 sources, with higher source strength at the beginning than at the end of the growing season. The key factors affecting NEE were soil temperature, LAI and species-specific photosynthetic capacities, coupled with phenology. ER was always influenced by soil temperature. Measurements of photosynthetic capacity indicated different responses among species to light intensity, as well as suggesting possible gains in response to future increases in atmospheric CO2 concentrations. Species- specific adaptation to low temperatures could trigger significant feedbacks in a climate change context. Our data highlight the need to quantify the role of dominant species in the C cycle (sinks or sources), as changes of vegetation composition or species phenology in response to climate change may have great impact on the regional CO2 balance
Carbon fluxes in Arctic plant species: photosynthetic performances, isotopic signature and VOCs emissions
No full textBVOC emission from Populus x canadensis saplings in response to acute UV-A radiation
No full textHybrid poplar (Populusxcanadensis) saplings were subjected to acute ultraviolet-A (UV-A) irradiation (30Wm2, ambient treatment, 60, 90 and 120Wm2 of UV-A irradiance) to determine the effects on photosynthesis and biogenic volatile organic compound (BVOC) emissions in two different short-term experiments (i.e. sequential increase in UV-A irradiance and UV-A intensityresponse relationships). Both intensityresponse experiments showed that the UV-A ambient treatment did not affect photosynthesis and BVOC emissions. Whereas exposition at 60, 90 and 120Wm2 of UV-A (first experiment), increasingly inhibited photosynthesis. This increasing inhibition was also detected by decreasing trends of both photochemical reflectance index (PRI) and fluorescence yield. Isoprene emission resulted to be very sensitive to increasing UV-A irradiances. Methanol was also very sensitive to high UV-A radiation, suggesting the occurrence of strong damages of cellular structures. The second experiment, which was performed both in the middle of July and repeated towards the end of the summer, showed a temporal variations in the UV-A intensityresponse relationships. In fact, there were no longer significant differences in photosynthesis, PRI and isoprene emission in response to high UV-A radiation toward the end of the summer season. The adaxial flavonoid level increased significantly over the period monitored, resulting 85% higher toward the end of the summer than during the middle of the summer. This dramatic increase in the adaxial flavonoids may have played a protective role against UV-A radiation by shielding leaves. Our findings add to the understanding of physiological processes involved in plant response to UV radiation
Isoprene emission aids recovery of photosynthetic performance in transgenic Nicotiana tabacum following high intensity acute UV-B exposure
No full textIsoprene emission by terrestrial plants is believed to play a role in mitigating the effects of abiotic stress on photosynthesis. Ultraviolet-B light (UV-B) induces damage to the photosynthetic apparatus of plants, but the role of isoprene in UV-B tolerance is poorly understood. To investigate this putative protective role, we exposed non-emitting (NE) control and transgenic isoprene emitting (IE) Nicotiana tabacum (tobacco) plants to high intensity UV-B exposure. Methanol emissions increased with UV-B intensity, indicating oxidative damage. However, isoprene emission was unaffected during exposure to UV-B radiation, but declined in the 48 h following UV-B treatment at the highest UV-B intensities of 9 and 15W m(-2). Photosynthesis and the performance of photosystem II (PSII) declined to similar extents in LE and NE plants following UV-B exposure, suggesting that isoprene emission did not ameliorate the immediate impact of UV-B on photosynthesis. However, after the stress, photosynthesis and PSII recovered in IE plants, which maintained isoprene formation, but not in NE plants. Recovery of IE plants was also associated with elevated antioxidant levels and cycling; suggesting that both isoprene formation and antioxidant systems contributed to reinstating the integrity and functionality of cellular membranes and photosynthesis following exposure to excessive levels of UV-B radiation. (C) 2014 Elsevier Ireland Ltd. All rights reserved
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
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