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Water relations of cucumber, tomato, and sweet pepper
No full textThe ever increasing importance of water as a critical resource for agricultural production has encouraged more research on water relations in recent years. Most attention has been paid to field crops and less information is available for horticultural crops, especially vegetables. The results of studies on water relations of cucumber, tomato, and pepper are reported and discussed in this thesis.Drying cycle experiments were carried out with tomato, cucumber, and sweet pepper at two temperatures and three light intensities in order to: (1) examine suitability of some plant parameters as criteria for expression of plant water status; (2) investigate which parameter is most suitable as a basis for timing of irrigation; and (3) observe the change of various parameters during a drying cycle as affected by environment. Measurements were carried out on transpiration rate, stomatal diffusive resistance ( rs ), leaf temperature, plant and soil water potentials, and relative water content. The transpiration rate at 25°C was in general higher than that at 21°C due to the higher vapour pressure deficit (vpd) at the former temperature. For all the three species, a more pronounced stomatal closure was demonstrated at 25°C as compared to that at 21°C when drought was imposed on the plants. This result could be due to the fact that at 25°C the vpd and/or the internal CO 2 concentration was higher. Various levels of irradiance did not invoke different responses of stomata or transpiration rates throughout the drying cycles. The difference among the three light intensities used are thought to have been too small to show distinct responses. Moreover, relatively low intensities were used in this series of experiments. The measured rs , values did not always correlate significantly with soil water potentials because rs , measurements were carried out on single leaves at only one point in the photoperiod and the measurements were also affected by other environmental factors, such as humidity, prevailing during the measurements. Calculated rs , values showed better correlations with soil water potential, presumably because transpiration rates of the whole plants over the entire photoperiod were used for their calculation. Relative water content and leaf water potential correlated significantly with soil water potential. Among the plant parameters studied, the plant water potential as measured with the pressure chamber, was judged as the most suitable parameter expressing plant water status.Some physical aspects of the internal plant water relations were considered for the three species. The measured parameters were relative water content, sap electrical conductivity, and leaf water potential and its components (osmotic, pressure, and matric potentials). The contribution of matric potential to the total plant water potential was considerable. Neglecting the matric component would result in unrealistically low levels of pressure potential for the three species. Tomato was considered to have the best osmotic and matric adjustments, followed by cucumber and pepper. Sap osmotic potential and electrical conductivity were found to be significantly correlated with leaf water potential. Electrical conductivity was considered as an easy and accurate method to determine the osmotic potential indirectly. From the regression of relative water content on leaf water potential, cucumber, tomato, and pepper showed, in this order, decreasing drought resistance. Examination of some other parameters, however, such as osmotic and matric adjustments and reduction of photosynthesis in stress conditions, confirmed a better drought resistance property to tomato, followed by cucumber and pepper. Relative position of cucumber and tomato in drought resistance was discussed. For all the criteria examined, pepper was considered to be the least drought resistant. It was concluded that a better understanding of the drought resistance mechanisms in plants is required.Carbon dioxide exchange and transpiration rates were measured in a gas exchange assembly in two series of experiments. In the first series, measurements were carried out on cucumber and pepper at light saturation and in darkness. In the second series, photosynthesis-light curves for cucumber, tomato, and pepper were obtained. For both series, well-watered as well as stressed plants were used. Both photosynthesis and transpiration were reduced as stress set in. It was shown that both stomatal and nonstomatal mechanisms were involved in the reduction of photosynthesis. For all the three species, an increase in mesophyll resistance was observed as a result of water stress. In experiments with different levels of irradiance, it was observed that the stressinduced reduction of photosynthesis was more pronounced at light saturation compared to low light. After showing some initial opening reaction to light, the stomata of stressed plants showed a closing pattern, especially for cucumber and pepper, regardless of irradiance levels. It was proposed that the closing effect of drought overrode the opening effect of light. Severely stressed plants of cucumber and pepper were rewatered to study their recovery. Photosynthesis did not reach the pre-stress level one day after rewatering, this was due to an aftereffect of drought on stomata in cucumber and pepper and a damage to the photosynthetic system in pepper.Diurnal changes in water relations parameters were measured in a glasshouse for tomato and pepper. In a constant environmental condition, gas exchange rates were monitored throughout the photoperiod for cucumber, pepper, and two cultivars of tomato. Both well-watered and stressed plants were used for the above measurements. In the glasshouse, transpiration, leaf water potential, stomatal diffusive resistance, as well as the diurnal changes in environmental factors such as radiation, temperature, vpd, and evaporation were measured. It was observed that the diurnal variation in leaf water potential followed that of transpiration. Changes in the whole plant transpiration were not necessarily accounted for by the rs values measured on single leaves. Multiple regression relationships were obtained for plant water potentials on radiation and temperature and suggestions were made to their use in timing of irrigation. In a constant environmental condition, all species showed maximum rates of transpiration and photosynthesis during the first hour of the photoperiod. The rates steadily declined thereafter, and the decline was more pronounced in stressed plants. A decrease in leaf water potential could not account for these diurnal phenomena, and other internal control mechanisms were thought to be involved. It has been suggested that photorespiration increased under the high irradiance employed. Internal CO 2 levels then increased, causing stomatal closure, leading to a decline in transpiration. Photosynthesis also decreased through both stomatal closure and a decrease in the CO 2 gradient. Increases in mesophyll. resistance in the case of cucumber and pepper also occurred.<p/
Response of eggplant to drought. I. Plant water balance
No full textEggplant (Solanum melongena L.) is known to have a higher resistance to drought than have other vegetables. Studies were made to see whether this property can be explained by its physiological responses. Water was withheld from plants and measurements were made of sap osmotic potential (ψos), leaf pressure potential (ψp), stomatal diffusive resistance to water vapour (rs), relative water content of leaf (RWC), whole plant transpiration, leaf water potential (ψleaf), and soil water potential (ψsoil). The first 4 parameters varied linearly with ψleaf and transpiration varied exponentially. There was a parabolic relation between ψleaf and ψsoil. The severely stressed plants were rewatered and underwent the same measurements 1 day later (“recovery treatment”). Compared with some other vegetables reported in the literature, ψp and RWC remained higher in droughted eggplant. This species has also a better stomatal control on transpiration. There was an after-effect of drought on the stomates. In recovery treatment, ψp values exceeded those of the control. This may have functional significance in resumption of growth after stress is alleviated
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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