117,399 research outputs found
Sensibilidade de respostas de fotossíntese foliar de cafeeiros após o experimento FACE: existe a memória?
No full textResumo: A hipótese deste trabalho foi que as respostas de fotossíntese de folhas de cafeeiros serão maiores em plantas que foram previamente cultivadas sob elevada concentração de CO2 (e[CO2]) do que nestas que sempre foram cultivadas sob a concentração atual de CO2 (a[CO2]), especialmente em condições de irrigação. Para estudar a existência de ?memória? positiva de e[CO2], o objetivo do estudo foi determinar variações de curvas de respostas de fotossíntese (A) na luz em folhas de café ao longo de perfil vertical de árvores, após um mês que o enriquecimento de CO2 foi encerrado no experimento FACE. As plantas previamente cultivadas sob e[CO2] apresentaram menor A comparadas com as que sempre foram cultivadas sob a[CO2]. O período transitório de rustificação (aclimatização) às condições de a[CO2] aumentou a sensibilidade das plantas cultivadas previamente sob e[CO2], especialmente estas sob irrigação. Em plantas continuamente cultivadas sob regime hídrico de campo e sob a[CO2], as folhas autossombreadas apresentaram maior resposta de A à concentração de CO2 de 590 ?L CO2 L-1 na câmara de medição na época de seca, como possível consequência de um ?estado de alerta?, para lidar com novos eventos de seca com sucesso. A hipótese de ?memória? em plantas previamente estimuladas com e[CO2] foi provada, mas ela induziu diminuição de A, por causa do aparelho fotossintético construído previamente no experimento FACE. ? Abstract: The hypothesis of this work was that the photosynthetic responses of coffee leaves would be promoted in plants that were previously cultivated under the elevated concentration of CO2 (e[CO2]) compared to those that were always cultivated under the current concentration of CO2 (a[CO2]), especially under irrigation conditions. To study the existence of positive ?memory? of e [CO2], the aim of this study was to determine variations in photosynthetic lightresponses curves of coffee leaves, estimated along the vertical tree profile, one month after the CO2 enrichment was terminated in the FACE experiment. Plants previously cultivated under e[CO2] showed lower leaf photosynthesis (A) compared to those always cultivated under a[CO2]. The transitional period of acclimatization (hardening) to the conditions of a[CO2] increased the sensitivity of plants previously cultivated under e[CO2], especially those ones under irrigation. In plants continuously cultivated under field water regime and under e[CO2], the self-shaded leaves showed higher A response to CO2 concentration of 590 ?L CO2 L-1 in the chamber during the dry season, as a possible consequence of a ?alertness? to successfully deal with new drought events. The hypothesis of ?memory? in plants previously stimulated with e[CO2] was proved, but it induced the reduction in A due to the photosynthetic apparatus previously built during the FACE experiment
Photosynthetic light curve parameters over vertical profile of Coffea arabica plants after five years of FACE experiment.
No full textTrends in climate changes indicate that the air [CO2] will continue to increase. The first plant response to elevated [CO2] (e[CO2]) is the increased photosynthetic rate. Photosynthetic rate dependence on light (A/PAR curves) is characterized by several parameters, often used to determine plant species responses to environment and phenological plasticity. The effects of water supply and phenological stage were expected, with no acclimation after long-term Coffea arabica L. cultivation under e[CO2]. The aim of the study was to determine variations in parameters of A/PAR curves in coffee leaves over a tree vertical profile after long-term cultivation under free-air-CO2-enrichment (FACE) system. The p arameters of A/PAR curves in C. arabica were estimated after five-years cultivation in FACE under two CO2 conditions, actual (a[CO2], ~390?L CO2 L-1) and e[CO2] (~590?L CO2 L-1), in two water regimes (rainfed and irrigation). The A/PAR curves were estimated in two phenological stages (grain formation - February 2016 and fruit maturation - May 2016). The A/PAR responses were determined by varying photosynthetic active radiation (PAR) from 1117 to 0 ?mol photons m?2 s?1 in four 50 cm-thick layers of vertical plant profile. The maximum photosynthesis (Amax), dark respiration (Rd), apparent quantum efficiency (?), and light compensation point (?) generally increased under e[CO2] compared to a[CO2], showing higher values during grain formation than during fruit maturation (Figure 1). The Rd and ? followed the progressive increase by layers only during the grain formation (Figures 1C and 1E). Continuation in e[CO2] stimulation indicated that leaf photosynthesis acclimation did not occur after five-years coffee cultivation under FACE. The lack of progressive increase in Amax, ? and ? over vertical profile indicates leaf plasticity to light availability, especially considering the high Amax of the two lowest layers. The compensation effects of e[CO2] to low water availability were observed in all A/PAR responses
Aspectos fotomorfogenéticos de plantas jovens de jatobá (Hymenaea courbaril L.).
No full textOrganizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Estimations of leaf CO2 assimilation, stomatal conductance and transpiration in adult Arabic coffee plants after long-term FACE cultivation.
No full textThe air [CO2] can reach 600 ?L CO2 L-1 in the middle or the end of this century, depending on scenario. The first plant response to elevated CO2 (e[CO2]) is the increased leaf photosynthetic rate (A) occurring parallelly by mainly non-sensitive or decreased stomatal conductance (gs) and decreased transpiration (E). In Arabic coffee, A increases under e[CO2], especially during the dry growing season, while gs responses vary during years under free-air-CO2-enrichment (FACE). The aim of this study was to estimate A, gs and E over a coffee vertical profile after five years cultivation under FACE, including the responses to water availability. Coffee was cultivated under two CO2 conditions, actual (a[CO2], ~390?L CO2 L-1) and e[CO2] (~590?L CO2 L-1). The irrigation started at the end of the 4th year of experiment. The measurements were conducted in rainy season, in February 2016 (grain expansion). Values of photosynthetic active radiation (PAR) varied from 1131 to 0 ?mol photons m?2 s?1 to construct curves of A, gs and E dependence on PAR in four 50 cm-thick layers. Simultaneously, PAR was measured in the morning, midday and afternoon. Punctual values were estimated from nonrectangular hyperbola (A) and polynomial (gs and E) models. PAR reached ~1400 ?mol m?2 s ?1 at the highest plant layer at midday, while the transmitted PAR at soil level was about 4 ?mol m?2 s?1. The A diminished gradually from plant top to bottom, from 7.2 to -1 ?mol m?2 s?1. The A was positively impacted by e[CO2] in the highest and low layers. The gs and E showed similar trends in daily variation and in responses to CO2 and water availability treatments, showing lower values under e[CO2] than a[CO2] over the plant profile, with exception of the most shaded leaves. Results suggest better water economy under e[CO2] than a[CO2] under high light conditions
Elevated air CO2 conditions changes the metabolic profile of Arabic coffee leaves during vegetative and reproductive stages.
No full textEffects of drought, elevated air CO2 and temperature can change the quality of food. Arabic coffee is characterized by biannual phenological cycle constituted by six stages: vegetative that occurs under long days, maturation of reproductive buds (MRB), flowering and grain expansion (FGE), grain formation (GF), grain maturation (GM) and senescence. We expected that leaf metabolic profile of plants cultivated under elevated CO2 would differentiate among stages of vegetative and reproductive growth. The aim of this study was to analyze those variations in Free-Air-CO2-Enrichment (FACE) experiment. In the 2nd year of growing under rainfed conditions in FACE, fully expanded coffee leaves were collected in four periods: June 2012 (MRB1-transformation of vegetative to reproductive buds), July 2012 (MRB2-relative bud dormancy), December 2012 (FGE) and January 2013 (GF). GCMS datasets, coupled with multivariate statistical methods, were used to investigate 35 compounds identified in coffee leaves growing in two CO2 conditions, actual (a[CO2], ~ 390?L CO2 L-1) and elevated (e[CO2], ~590?L CO2 L-1). Mainly, the content of amino, fatty and organic acids besides phenolic compounds and sterols, diminished under e[CO2] (Table 1). Only the content of dodecanoic (GF) and citric (MRB1) acids increased. Under e[CO2], both reduction or increase in leaf carbohydrate contents occurred. Sugar alcohols as mannitol (FGE), galactitol (FGE) and pinitol (MRB1) showed 16, 22 and 37 times higher content under e[CO2] than a[CO2], respectively. The PCA showed an obvious separation in CO2 treatments, differing metabolites in all stages, not only vegetative from reproductive ones (Figure 1). The high leaf investments in carbohydrates, specifically sugar alcohols, indicates quick investments of carbon in metabolites under e[CO2]. Higher levels of citric and dodecanoic acids under e[CO2] than a[CO2] suggest the mitigation of various stress conditions under e[CO2], as drought, low/high temperatures and presence of coffee leaf rust attack, which were observed along the experimental period
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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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