1,720,992 research outputs found
Microbial-mediated feedbacks of leaf litter on invasive plant growth and interspecific competition
No full textFeedbacks between plants and soil microbes can play an important role in competition between potential invaders and the resident community. However, the role of saprophytic soil microbes is poorly understood because research largely focuses on the role of specific soil-borne pathogens. Our aim was to examine the role of plant-saprophyte feedbacks in soil processes (decomposition and enzyme activities) and plant competition. We preconditioned a common soil in microcosms by decomposing litter of four species; two exotic invasive species (Microstegium vimineum and Berberis thunbergii) and two native species (Viburnum acerifolium and Vaccinium corymbosum). We then replaced the litter with either the same species' litter or a different species' litter on the preconditioned soil. We measured the effect of preconditioning on subsequent litter decomposition, microbial community structure (phospholipid fatty acids) and function (soil enzyme activities and decomposition). We then grew Berberis and Viburnum seedlings in preconditioned soils under intraspecific and interspecific competition to determine whether litter preconditioning had a feedback effect on competition. Changes in microbial community structure during preconditioning persisted through time and altered subsequent soil enzyme activities and litter decomposition. These changes also affected the growth rate of two shrub species, but because both shrubs grew best in soil that previously contained Berberis litter, competition between these species was not directly affected. Plant litter creates a legacy that influences the future structure of the microbial community even after that litter is gone. This legacy effect has functional consequences on decomposition and plant growth, and could be an important but under-appreciated factor in soil and plant community ecology. Further study is needed to determine how these consequences affect plant community composition and invasibility.National Science Foundation [DEB-0309047
The community-level and ecosystem-level consequences of feedbacks between the soil ecosystem and the plant community during forest understory invasion
No full textThis dissertation addresses the consequences of reciprocal interactions between the plant and the soil microbial communities, and how those interactions affect nutrient cycling and plant competition during exotic plant invasion. Each chapter is linked by the common theme of evaluating the importance of these feedbacks to the rate of plant invasion in the forest understory. In the first two chapters, I utilize microcosms to evaluate the importance of leaf litter inputs for plant-soil feedback. The first chapter demonstrates that leaf litter from native and exotic plants create divergent soil microbial communities, altering soil enzyme activities and nitrogen cycling, which in turn affects the growth of native and invasive plants. However, while this plant-soil interaction affects growth rate, it does not change the competitive hierarchy or the success of the invasive plant. The second chapter shows how the effect of an exotic species' leaf litter on soil microbes varies over a range of invasion severity. Using litter mixtures ranging from 0% to 100% exotic litter, I show that ecosystem-level effects of invasion on carbon and nitrogen cycling are linearly related to the exotic plant density, while community-level effects on soil microbes are non-linear and very sensitive to low levels of invasion. In the final chapters, I extend these results to examine whole-plant effects in more natural plant communities. The third chapter uses a large-scale field experiment to explore the temporal dynamics of invasion impacts. I show that the short-term impact of native and invasive plants on soil microbes is weak, while long-term effects are much stronger. However, after restoration of native plants, the legacy effect of invasion remains strong. Using experimental litter-removal, I also show that belowground plant litter more strongly influences the soil microbial community than aboveground litter. The fourth chapter examines how the diversity of the native community influences the invasion impact on soils. I show that while diversity has little direct effect, individual native plant species can influence how an exotic invasive shrub affects the soil ecosystem. Together, these results show that the importance of plant-soil feedbacks for exotic invasion is context- and scale-dependent, exhibiting nonlinear dynamics that depend on the native community and the degree of invasion, and vary in strength over time.Ph.D.Includes bibliographical referencesIncludes vitaby Kenneth John Elgersm
Legacy effects overwhelm the short-term effects of exotic plant invasion and restoration on soil microbial community structure, enzyme activities, and nitrogen cycling
No full textPlant invasions can have substantial consequences for the soil ecosystem, altering microbial community structure and nutrient cycling. However, relatively little is known about what drives these changes, making it difficult to predict the effects of future invasions. In addition, because most studies compare soils from uninvaded areas to long-established dense invasions, little is known about the temporal dependence of invasion impacts. We experimentally manipulated forest understory vegetation in replicated sites dominated either by exotic Japanese barberry (Berberis thunbergii), native Viburnums, or native Vacciniums, so that each vegetation type was present in each site-type. We compared the short-term effect of vegetation changes to the lingering legacy effects of the previous vegetation type by measuring soil microbial community structure (phospholipid fatty acids) and function (extracellular enzymes and nitrogen mineralization). We also replaced the aboveground litter in half of each plot with an inert substitute to determine if changes in the soil microbial community were driven by aboveground or belowground plant inputs. We found that after 2 years, the microbial community structure and function was largely determined by the legacy effect of the previous vegetation type, and was not affected by the current vegetation. Aboveground litter removal had only weak effects, suggesting that changes in the soil microbial community and nutrient cycling were driven largely by belowground processes. These results suggest that changes in the soil following either invasion or restoration do not occur quickly, but rather exhibit long-lasting legacy effects from previous belowground plant inputs
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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