1,720,968 research outputs found
Effet de vers de terre sur les plantes (du fonctionnement individuel à la structure des communautés végétales)
No full textLes vers de terre constituent une composante majeure de la faune du sol et il est désormais bien établi qu ils affectent la croissance des plantes. Bien que les espèces de plantes répondent différemment aux vers de terre au cours d un cycle de vie, très peu de travaux ont étudié l effet des vers de terre sur la compétition entre plantes et sur leur démographie. Les vers de terre peuvent affecter la stratégie d allocation des ressources des plantes et ainsi, influencer leur survie et leur fécondité. Ils pourraient donc affecter la démographie de différentes espèces de plantes et donc, au-delà d une génération, la structure des communautés végétales. Nous avons étudié dans une série d expériences l effet d un ver endogé (A. caliginosa) et d un ver anécique (L. terrestris) et de leur interaction sur quatre plantes annuelles (T. dubium, V. persica, P. annua et C. glomeratum) du niveau individuel (réponse de chaque espèce végétale considérée individuellement) au niveau de la communauté végétale (réponse des plantes en situation de compétition au sein d une communauté végétale). Nous avons ainsi montré que les vers de terre affectent la croissance des plantes et que cet effet varie en fonction de l espèce végétale et du type de sol utilisé. De plus, ils modulent la compétition entre plantes sur le court et le long terme et leurs effets sur les plantes peuvent être transmis à la génération suivante, par un effet maternel. Enfin, ils modifient la démographie des plantes en influençant leur fécondité, leur survie et la germination des graines. Dans une expérience en mésocosmes qui a maintenu pendant trois générations des communautés des quatre plantes annuelles avec et sans vers, nous avons pu vérifier que les mécanismes démographiques mis en évidence dans les expériences à court terme modifient bien la structure de la communauté sur le long terme. Toutefois, il apparaît pour le moment impossible de prédire quelles espèces végétales vont bénéficier des vers de terre. Cela est probablement dû à l action simultanée de nombreux mécanismes en interaction. Il reste à étudier ces interactions, et à construire un cadre conceptuel permettant de prédire quels groupes fonctionnels de plante vont bénéficier de l action des vers de terre à court et long terme, c est à dire en terme de biomasse et de nombre d individus.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Earthworm-mediated maternal effects on seed germination and seedling growth in three annual plants
No full textMany ecological studies have pointed out maternal effects in plants and shown that plant maternal environment influences germination of their seed and subsequent seedling growth. However, few have tested for maternal effects induced by soil macroorganisms. We tested whether two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) trigger such maternal effects on seed germination and seedling growth of three plant species (Veronica persica, Poa annua and Cerastium glomeratum). Our results show that, through maternal effects, A. caliginosa enhanced seed germination (V. persica and P. annua) and seedling growth (C. glomeratum and P. annua) while L. terrestris reduced seed germination only in V. persica. In some cases, the increase in germination rates of seeds produced in the presence of earthworms was associated with a reduction of nitrogen content in seeds. These results show that earthworms induce maternal effects in plants and that the size and direction of these effects depend on the combination of plant and earthworm species
Soil aggregation, invertebrates and litter quality in laboratory experimentation: interactions between earthworms and woodlice
No full textInternational audienc
Soil aggregation in a laboratory experiment : interactions between earthworms, woodlice and litter palatability
No full textInteractions between soil invertebrate functional groups are still poorly understood. In this study, the effect of the soil dwelling earthworm Aporrectodea caliginoso and the woodlouse Porcellio scaber (litter inhabitant), atone or in combination, on soil aggregation was investigated in laboratory microcosms with litter of different quality (Quercus robur and Fagus sylvatica). After 4 months of incubation, the aggregate size distribution was measured using a dry-sieving method. A. caliginosa played an important role in the formation of large aggregates (> 2 mm), whereas P scaber greatly influenced litter disappearance. A. caliginosa individuals formed a greater number of large aggregates when fed with beech leaves compared to oak leaves even though they preferred the latter. In the presence of beech and P scaber, A. caliginosa produced significantly fewer large aggregates than expected
Soil aggregation, invertebrates and litter quality in laboratory experimentation: interactions between earthworms and woodlice
No full textInternational audienc
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
Impact of pruning intensities on cocoa tree productivity, pest (mirids) and disease (black pod disease) infestations on farmer field trials in Côte d'Ivoire
No full text<p>The current study was carried out to evaluate short term effects of pruning intensities on fruit set, pod health and yield responses in mature trees of 10 to 15 years old. Two different pruning intensities (Removal of 20% removal of secondary branches and removal of 40% of secondary branches) were compared to unpruned trees (Control). We investigated also whether effects of pruning intensities vary across agroecological zones (deciduous and evergreen forest zones). Five cooperatives distributed in two agroecological zones were selected (two in deciduous zone and three in evergreen forest zone). Five trial sites were installed per cooperative each with the 3 pruning treatments (unpruned Control, 20% pruning and 40% pruning). Pruning treatments were applied the first time in April 2020 then renewed in April 2021. Various observations on yield parameters i.e., pod size, number of pods (healthy, mirid infected, black pod infected), number of beans per pod, fresh bean weight and dry bean weight were recorded for each plot at every harvest event (started in main crop 2020) for both light and main crops. </p><p>Experiment results revealed that during the first year of trial (20/21 crop season) both pruning intensities increased dry bean yield. However, the lighter pruning intensity (20% pruning) was more suitable in transitional zone as it showed higher yield (648.5 Kg/Ha) compared to heavy pruning (40% pruning and 591,2 Kg/Ha) and unpruned control (522Kg/Ha). In evergreen forest zone, heavy pruning showed higher yield (890,5 Kg/Ha) compared to light pruning (832,5 Kg/Ha) and unpruned control (742,4 Kg/Ha). During 21/22 main crop both pruning intensities delivered comparable yield results in the two agroecological zones (600 Kg/Ha) but were still higher than unpruned control (500Kg/Ha). Pruning decreased mirid (52% and -60% respectively for 20% and 40% pruning intensity) and black pod -<i>Phytophtora </i>(-43% and -45% respectively for 20% and 40% pruning intensity) infestations over crop seasons. </p><p>Our results confirmed that pruning is a key lever for reducing mirid and black pod disease infestation and improving productivity which contributes to increasing farmer income. Our findings showed also that light pruning is suitable in transitional zones when starting the implementation. Finally, by improving pod health pruning could contribute to improvement of beans quality by reducing the level of free fatty acids (FFA) that are favored by fermentation of poor-quality beans. The link between pruning and improvement of bean quality and potential for reducing FFA level is currently being investigated on our trial sites. </p><p><strong>Keywords</strong>: pruning, mirids, black pod disease, yield, cocoa productivity</p>
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