1,720,962 research outputs found
Soil Protists: From Traits To Ecological Functions
No full textThe best-known function of soil protists is as bacteria feeders, protists consume bacteria prey and further release the nutrients which were locked in bacteria biomass, those nutrients benefit the remaining bacteria and plant root. Moreover, protists do not feed on all prey bacteria equally, this selective feeding by protists can lead to shifting prey bacterial community structure, which may be linked with changes in soil community functioning. Given the lack of a generalized pattern of protists predation, the central question of this thesis is whether the effects of protist predation can be predicted. I proposed to use protist traits as a means to address this question. Due to the focus of previous work on only one model protists and some closely related protists, I then collected and isolated 20 protists species with diverse morphotypes to investigate the central question.
I started by clarifying the taxonomic affiliations of the protists isolates used in this thesis, with a special focus on Heterolobosea amoeba, which are widespread and diverse in soil. Given the lack of morphologically useful characteristics in Heterolobosea amoeba, I further combined morphological characterization and molecular tools to identify these species and proposed a new species Vahlkampfia soli. This first soil Vahlkampfia species highlights the need for additional efforts in the future to cultivate previously unknown soil protists.
I continued to investigate the relationship between protist traits and their effects on prey bacterial community structure. I measured a range of protists traits across my target 20 protist species covering the main phylogenetic lineages found in soil. I further used microcosm experiments to assess the effect of each species on the structure of a semi-natural soil bacterial community. This work revealed that protists traits, especially cell volume, could be linked to their predation effect on the bacterial community. It was critical that cell volume calculations were not only based upon cell size but also considered geometric morphotype.
To understand the functionality of protists, I then examined how protist predation and competition with other soil bacteria communities affect the stability of bacterial cooperative interactions. I utilized two types of bacterial strains, one is a cooperator bacterial strain that produces the public goods, the other one is defector bacterial strain that takes advantage of public goods without contributing to their production. I combined these two types of bacteria in the presence of competing soil bacterial communities and protists. This work revealed that multitrophic interactions strongly impacted microbial cooperation, in particular, competition increased the net benefit of cooperation at low and intermediate resource availabilities, however, predation followed the opposite pattern. Moreover, multitrophic interactions constrained the defector invasion and promote cooperation, but this effect strongly depended on resource availability.
Finally, I synthesized existing knowledge on soil protists and demonstrate their importance as regulators of the rhizosphere microbiome. I then addressed the known and hypothesized consequences of protists on microbiome functionality and plant performance. I also presented a framework to guide efforts to harness protists as a microbiome enhancer in sustainable agriculture
The antagonists and helpers of plant pathogens: unraveling interactions that determine pathogen success
No full textA range of soil-borne diseases is increasingly threatening agricultural production around the world. As production demands increase, there is a pressing need to reduce the use of environmentally unfriendly pesticides and agrochemicals. To address this need, plant root-associated microbiomes are increasingly being seen as a possible solution to boost natural pathogen resistance and soil microorgniams have become a target for innovative strategies aiming at improving crop protection. However, the ability of rhizosphere microbial communities to keep diseases under control is influenced by many factors, including the microbial interactions within these communities. Unfortunately, we still have relatively little insight into how microbial interactions affect community assembly and how such interactions eventually impact plant health. This thesis seeks to examine how microbial interactions within the rhizosphere microbiome impact the ability of plant pathogens to proliferate and cause plant disease. To this end, this thesis used bacterial wilt disease in tomato plant, which is caused by pathogen Ralstonia solanacearum, as a relevant model system.
In Chapter 2, I have combined direct examination of the plant-associated microbiomes from healthy and diseased tomato rhizosphere soils with interaction studies in the laboratory involving bacterial isolates recovered from these soils. Results showed that rhizosphere microbial communities were one of the important factors influencing the manifestation of disease. However, correlation analyses showed discrepancies between co-occurrence patterns and direct strain interactions. This suggests that positive or negative links within co-occurrence networks are poor predictors of actual one-on-one interactions of bacterial populations.
I subsequently used controlled systems with synthetic microbial communities to disentangle the role of specific organisms and their interactions in the ecological processes associated with bacterial wilt disease suppression. In these simplified systems, Chapter 3 assessed how interactions among antagonistic strains influenced pathogen invasion, and Chapter 4 tested if control of the pathogen can be achieved indirectly though inhibition of pathogen helpers. Results showed that in addition to the direct interactions between rhizobacterial isolates and the pathogen, indirect effects from interactions among rhizobacterial isolates could also be strong determinants of pathogen success. These results suggest that instead of a purely pathogen-focused view, better solutions for controlling plant disease outbreaks may be achieved by managing the composition of the soil microbiome as a whole.
Chapter 5 examined the extent to which microbial interactions were influenced by resource availability. I found that at high resource availability, competitive resident communities produced more antimicrobial compounds, making them less susceptible to invasion compared to more facilitative communities. At low resource availability, facilitative communities reached higher productivity, which in turn was more important for resistance to pathogen invasion than the competitive interactions in such less productive communities. Therefore, in the study of microbial interactions in the rhizosphere, it is important to consider the effects of relevant environmental factors such as nutrient availability.
Taken together, the results of this thesis form the basis for more informed management strategies based on knowledge of microbial interactions and community assembly, ultimately aiming to improve soil-borne disease suppressive potential in a targeted fashion without the use of pesticides
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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