1,721,056 research outputs found
Long Term Impacts of Farming Practices on Carbon, Water and Microbes in a Mediterranean Ecosystem
Get PDFThis dissertation investigates how management with different combinations of practices, namely mineral N fertilizer, cover cropping, compost amendment, furrow irrigation and subsurface drip irrigation have impacted soil carbon, nutrients, and microbial communities in a 25-year long term experiment. First, I investigated how subsoil carbon stocks have increased under a combination of compost and cover crops after 25 years. I found that a potential synergistic effect between soluble C, soluble N and soil pores created by cover crop roots that allowed for greater C and N transport to subsoils. This transport of soluble C and N was associated with reduced microbial stress levels, and potentially longer C residence times. Secondly, I looked at how soil microbial community structure and microbial functional potential changed after 20 years of management practices intended to improve soil health. I found significant changes in functional potential for C breakdown and N transformation, but no significant changes in microbial community structure. These changes in functional potential were associated with changes in soil health measurements and may indicate the potential impact of practices intended to improve soil health. Finally, I examined how soils under a combination of compost and cover crops changed carbon and nutrient distribution under 5 years of subsurface drip irrigation (SDI) and furrow irrigation. I found that soils under SDI and furrow irrigation only differed in carbon and nutrient distribution in the top 30 cm, and that furrow irrigation was associated with a loss of surface organic matter after 5 years while SDI was not. The differences in spatial distribution and amount of water under SDI vs furrow irrigation may not significantly reduce the amount of carbon and nutrients stored in subsoils but may have an impact on surface organic matter content. In conclusion, the impacts of management practices on soils with similar climate and mineralogy may be difficult to measure over the course of a single season, but these impacts may accumulate over multiple years to result in significant shifts in soil edaphic and microbial properties
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Investigating soil and gut microbial communities and connections with child health in rural Kenya
No full textSoils contain diverse and dynamic communities of microbes that interact with, and influence, microbiota in and on plants, animals, and humans. These exchanges, such as between soil and human microbiota, are part of a vast, integrated microbial ecosystem that underpins much of terrestrial life on Earth. This dissertation addresses relationships between soil microbiota and human microbiota, and their connections with human health. I approached these investigations by collecting and compiling a range of data spanning soil microbiota, child gut microbiota, health and disease factors, household characteristics, and biophysical landscape characteristics among 144 households across three rural counties in western Kenya. Using these data I first investigated the variation in gut microbial communities between children living in different rural environments, including agriculture, rural settlements, and uncultivated forest and shrubland landscapes. Although we did not find differences in child gut microbial diversity between children from these different landscapes, we found (1) significant differences in abundances of specific gut microbial taxa that are associated with health and disease, and (2) landscape-level differences in the taxa that discriminate children with a recent diarrheal episode from those without. These findings are initial evidence of a potential landscape association with the child gut microbiota, with implications for understanding childhood diarrheal disease burden. Next I investigated the relationship between the child gut microbial community and the soil microbiota in children’s households using a microbial source tracking approach. I found that the proportion of the gut microbiota attributed to soils (S2F proportion) varied among households, and in some was greater than a third, indicating a significant relationship between soil and gut microbiota at the household level. Furthermore I observed that S2F proportions were notably higher in households where I collected data later in the region’s seasonal rainy-dry cycle. Using three complementary regression modeling approaches, I examined potential correlates of S2F proportion from among the household and landscape biophysical data. I found stronger associations among soil and climate characteristics than among household and social factors, and soil pH and seasonal precipitation had the greatest association with S2F proportion. These results demonstrate the potential involvement of seasonal climate and soil properties in the relationship between the child gut microbiota and soil microbiota. Finally, I evaluated the capability of the soil and fecal microbiota to predict child and household characteristics using a series of machine-learning based classifier models. Utilizing only the fecal microbial data, the classifier successfully identified household-level landscape classes. With soil microbial data, the model successfully classified households by their landscape classes, soil classes, drinking water source, and season of sampling. A relatively small number of soil taxa were more important in the model’s performance, including taxa commonly found in the human gut. These findings indicate that a seasonal change in soil microbiota may influence the composition of the child gut microbiota in rural households. Altogether, this research presents novel evidence that household- and landscape-level exposures, including to soil microbiota, are strongly associated with the human gut microbial community, and that these associations hold potential implications for health and disease
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Interactions Between Enhanced Rock Weathering, Organic Amendments, and Microbial Communities Influence Soil Carbon Sequestration
No full textImproved management practices are needed to mitigate climate change and maintain soil health for agricultural sustainability. One management practice that has garnered significant attention for its potential to sequester atmospheric carbon as inorganic carbon (IC) is Enhanced Rock Weathering (ERW). This process involves the application of crushed silicate minerals to soils to accelerate geochemical weathering processes. To date, research has focused largely on quantifying weathering rates and IC formation. However, the use of ERW in combination with organic inputs and the impacts of this combined practice on soil organic carbon (SOC) and microbial dynamics remain underexplored. To address this knowledge gap, this dissertation investigates the impact of combining organic inputs with ERW on SOC fractions, microbial biomass, community composition, and mineral weathering.In chapter 1, I present a three-year field study conducted in California agricultural soils that evaluated ERW interactions with compost and biochar under conventional management practices. The field application of crushed silicate minerals showed evidence of weathering, with increased pH and IC, along with an increase in SOC compared to soils without rock amendments. Combined rock and organic amendments further enhanced weathering, but reduced SOC and nitrogen content in organic fractions, such as mineral associated organic matter, compared to organic inputs alone. In chapter 2, microbial community dynamics were assessed over time within the same field experiment as chapter 1. Soil bacterial communities responded quickly to rock amendments, while fungal communities exhibited a more gradual but pronounced response to combined amendments. Co-applying organic inputs with rock treatments enhanced microbial diversity, which may have contributed to observed SOC and N losses by influencing microbial decomposition dynamics. These shifts in microbial communities are particularly relevant to soil health and carbon management, as they suggest that rock and organic inputs together can alter nutrient cycling and organic matter stabilization.Finally, chapter 3 involved complementary microcosm experiments incubated field soils with crushed olivine and glucose. I investigated how microbial carbon use and allocation interact with inorganic inputs in the formation of SOC across weathering stages. In controlled microcosm experiments, crushed silicate minerals alone reduced microbial biomass, but when combined with glucose, they stimulated microbial growth and increased SOC content after 55 weeks. The addition of glucose to the silicate treatment led to greater short-term IC formation—though this effect diminished over time—and long-term SOC retention than glucose alone due to increased microbial carbon allocation to stable SOC fractions. These findings demonstrate that combining ERW with organic amendments may optimize IC sequestration and SOC stabilization but also introduce trade-offs that require careful management. In the field, co-applying rock and organic amendments increased pH and IC but slowed SOC and N accumulation. Microcosm results showed ERW promotes short-term IC formation with uncertain long-term sequestration, while its combination with organic inputs increased microbial contributions to long term SOC. By bridging geochemical and biological processes, this study shows that organic inputs are critical microbial energy sources that enhance the long-term effectiveness of ERW. This study provides actionable insights for deploying ERW as a climate-smart soil management strategy with significant potential to advance sustainable carbon sequestration and agricultural productivity
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
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Comparative Multifunctionality of Dryland Annual and Perennial Grain Production Systems in a Mediterranean Climate
Get PDFAgricultural stakeholders are becoming increasingly aware of the need for sustainable food systems. In a shift from an agricultural paradigm that prioritizes yield, there is now growing interest in multifunctional food systems that simultaneously promote environmental integrity while also providing adequate yield and nutrition. An investigation into how current and proposed alternatives to annual grain systems address the multifaceted objectives of food system sustainability is necessary given that annual grains currently comprise nearly 70% of earth’s cultivated land and provide majority of the world’s food. Furthermore, it is crucial to conduct research on these grain systems in highly productive and economically valuable agroecological regions, such as California (CA). As the largest and most diverse agricultural state in the U.S., CA provides market opportunities while also heralding what current and future food systems must overcome to maintain food supply amid projected water and weather extremes. Thus, we investigated the multifunctionality of a tilled annual wheat system and two proposed alternatives, no-till annual wheat production and novel perennial grain production, in the Mediterranean climate of California. We measured plant and soil parameters for three years in intermediate wheatgrass or IWG, no-till annual wheat, and tilled annual wheat at four nitrogen rates. IWG had significant fluctuations in aboveground biomass (AGB) and had the highest soil carbon (C) mineralization at each soil depth. No-till wheat had stable AGB and the highest soil C stabilization and microbial biomass in the topsoil, which suggests plant productivity and a lack of soil disturbance over time are key factors underpinning enhanced soil C stabilization and gains in microbial biomass in the topsoil. Yield stability, soil carbon storage and nitrogen use efficiency (NUE) were then compared among the three systems using a multifunctionality framework. IWG had large interannual fluctuations in grain yield and NUE, while annual wheat (till and no-till) had stable grain yields and higher NUE than IWG. Soil carbon gains in IWG and no-till wheat relative to the tilled wheat were contingent upon N fertilization and constrained to the topsoil, while tilled wheat stored carbon at depth and across the whole soil profile. Finally, soil microbial community composition and soil carbon were compared in tilled annual wheat and IWG during the final year of the experiment. Bacterial community composition was more sensitive to soil depth than crop type, whereas fungal community composition was influenced largely by crop type. While the fungi : bacteria ratio was higher in IWG at deep soil depths, tilled annual wheat had a higher abundance of fungal taxa known to positively correlate with soil carbon and higher soil carbon mass than IWG at the 60-90 cm soil depth. The two major takeaways from this three-year field experiment were: 1) sampling the subsoil (> 30 cm) is crucial when comparing system-level soil carbon storage potential of annual and perennial grain systems; and 2) plant productivity underpins numerous components of agricultural multifunctionality and thus plant adaption is of utmost importance when designing and implementing future food systems
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
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