Dissertations / Theses on the topic 'Carbon and nitrogen stocks'
To see the other types of publications on this topic, follow the link: Carbon and nitrogen stocks.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Carbon and nitrogen stocks.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Silva, Jéssica Caroline dos Santos. "Estoques e fluxos de carbono e nitrogênio acima e abaixo do solo em fragmentos de Floresta Atlântica no sul do Brasil." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/64/64135/tde-30112017-101614/.
Full textAbstract:
Florestas tropicais tem um papel relevante nos ciclos globais do carbono e nitrogênio. A Floresta Atlântica é um bioma tropical ameaçado da América do Sul, de imensa complexidade estrutural, mas ainda pouco investigado quanto ao seu funcionamento. Neste contexto, o objetivo principal desse estudo foi investigar a estrutura da floresta através da quantificação da biomassa viva acima do solo e da queda anual de folhas. Paralelamente, as concentrações de carbono e nitrogênio foram determinadas no solo, e na vegetação, permitindo a determinação de estoques e fluxos desses elementos em áreas de diferentes fitofisionomias localizadas nas escarpas da Serra do Mar, na costa nordeste do Estado de Santa Catarina, sul do Brasil. As áreas de estudo localizam-se no município de Joinville, onde a temperatura média anual é de 20°C e a precipitação média acumulada anualmente é de aproximadamente 2200 mm. Os sítios amostrais foram estabelecidos em elevações de 200 m anm (Submontana) e 800 m anm (Montana) Em cada área, quatro parcelas de aproximadamente 0,25 ha foram delimitadas, e, então, foram determinadas a estrutura florestal, biomassa acima e abaixo do solo (viva e morta) e produção de serrapilheira. Concentração e composição isotópica de carbono e nitrogênio em cada compartimento (folhas, tronco, serrapilheira e solo) foram determinadas e usadas para converter biomassa em estoques e fluxos desses elementos, e compreender as complexas interações dentro desses ecossistemas. A AGLB foi de aproximadamente 300 Mg.ha-1 na floresta Submontana e 380 Mg.ha-1 na floresta Montana, AGDB, por sua vez, foi de 6,8 e 6,6 Mgoha-1 e BGB (raízes) foi de 54 e 66 Mg.ha -1, respectivamente. Não foi encontrada diferença significativa entre a produção de serrapilheira entre as fitofisionomias, sendo encontrada uma produção média de 6,4 Mg.ha-1 ano-1 na floresta Submontana e 6,9 Mg.ha-1 ano-1 na Montana. As folhas foram o componente majoritário da serrapilheira, contribuindo com ~68% em ambas as áreas. Os estoques totais de carbono e nitrogênio foram significativamente maiores na fitofisionomia Montana, aumentando de 208 MgC.ha-1 para 390 MgC.ha-1 e de 7 MgN.ha-1 para 16 MgN.ha-1, respectivamente. Fluxos de carbono e nitrogênio via serrapilheira nas florestas Submontana e Montana foram, respectivamente, igual a 3,0 e 3,2 Mg.ha-1 e de 0,12 e 0,14 Mg.ha-1. Valores de ?13C em cada compartimento foram similares entre as áreas, e típico de plantas que seguem o ciclo fotossintético C3. Conforme esperado, um enriquecimento em 13C e 15N ao longo do perfil do solo foi encontrado em ambas as áreas. Valores de ?15N foram maiores em folhas, serrapilheira e solo na floresta Submontana, possivelmente devido à maior disponibilidade de nitrogênio neste sítio; e/ou ao baixo tempo de residência do solo e serrapilheira empobrecida em 15N no sítio Montana. De maneira geral, posições latitudinal (em termos de disponibilidade de luz) e altitudinal (em termos de precipitação e temperatura) foram determinantes na composição, alocação e dinâmica do carbono e nitrogênio nestes ecossistemasTropical evergreen forests have a key role in the global carbon and nitrogen cycles. The Atlantic Forest is a vanishing South American tropical biome of immense structural complexity. The structure and functioning of these forests are relatively unknown. In this context, the main objective of this study was to investigate the forest structure by estimating aboveground live biomass (AGLB), belowground biomass (BGB) and litterfall. The determination of carbon and nitrogen concentrations in soils and vegetation allowed to quantify stocks and fluxes of these two elements. Four 0.25 ha-plots were established in two elevations (200 m asl and 800 m asl) in forests located on the slopes of the Serra do Mar, on the northeast coast of the State of Santa Catarina, southern Brazil. The sampling areas are located in the municipality of Joinville. The historical average annual temperature is 20°C and rainfall is approximately 2200 mm. The AGLB varied along the sites from approximately 300 Mg.ha-1 (submontane) to 380 Mgoha-1 (montane), AGDB varied from 6.8 to 6.6 Mgoha-1 and BGB (roots) varied from 54 to 66 Mg.ha -1, respectively. . The average litterfall production of 6.4 Mg.ha-1 ano-1 and 6.9 Mg.ha-1 ano-1 were found in the submontante and montane study sites, respectively. Leaves were the major component of litterfall contributing ~68% in both sites. Total carbon and nitrogen stocks were higher in the montane site. Total carbon stock (AGLB + BGB) increased from 208 Mg.ha-1 in the submontane site to 390 Mg.ha-1 in the montane. While, total nitrogen stock increased from 7 Mg.ha-1 to 16 Mg.ha-1, respectively. Fluxes of carbon and nitrogen via litterfall in the submontane and montane site varied from 3.0 to 3.2 Mg.ha-1 and from 0.12 to 0.14 Mg.ha-1, respectively. ?13C values in each compartment were similar between the two sites, and representative of C3 plants. As expected, there was an enrichment of ?13C and ?15N values in depth in each studied site. ?15N values where higher in leaves, litter and soil of the submontane site, possibly due higher nitrogen availability in this site; or low residence time of soil and depleted 15N in litterfall of the montane site. Overall, latitutinal (in terms of light availability) and altitudinal (in tems of precipitation and temperature) position were determinant in the nitrogen and carbon composition, allocation and dynamics in these ecosystems
2
Kyulavski, Vladislav Dimitrov. "Greenhouse gas emissions and soil carbon stocks associated with crop residues and organic fertilizers mixtures in sugar cane cropping systems." Thesis, La Réunion, 2019. https://elgebar.univ-reunion.fr/login?url=http://thesesenligne.univ.run/19_27_VDKyulav.pdf.
Full textAbstract:
Dans le contexte environnemental actuel il est nécessaire d’optimiser l’utilisation des ressources pour réduire les déchets et les émissions de gaz à effet de serre (GES). L’utilisation de ressources renouvelables et le recyclage sont au cœur du modèle d’économie circulaire, selon lequel le déchet est une ressource mobilisable, transformable, réutilisable et par conséquent non limitée. En agriculture, le cercle vertueux de l’économie circulaire peut être mis en place à travers le recyclage des matières organiques en tant que fertilisants et l’adoption d’une approche agroécologique qui privilégie les services écosystémiques pour lutter contre les nuisibles, protéger le sol et augmenter ses stocks de carbone, dont un des exemples est le paillage. Dans la culture de canne à sucre, la paille laissée à la surface du sol, est aussi de plus en plus convoitée par les industriels pour la production d’agrocarburant de seconde génération. L’émergence d’une telle concurrence d’usage de la biomasse et les enjeux environnementaux sous-jacents imposent d’évaluer à la fois les avantages et les inconvénients agronomiques et environnementaux du recyclage conjoint du paillis de canne à sucre et des fertilisants organiques. Les objectifs de ce travail sont donc i) de comparer l’effet des fertilisants de qualité physicochimique contrastée, sur la décomposition d’un paillis de canne à sucre, et ii) d’évaluer les potentialités d’émission de GES des mélanges paillis-fertilisant en fonction de la quantité de paille laissée et de la qualité des fertilisants apportés. La stratégie de recherche adoptée visait dans un premier temps à détecter des interactions carbone/azote lors du recyclage conjoint de la paille et des fertilisants organiques. Nous avons ainsi testé la prédictibilité des dynamiques de minéralisation du C et du N des matières organiques seules, ou en mélange (paille/fertilisant) en laboratoire, par un modèle additif simple et un modèle mécaniste de transformation du carbone et de l’azote dans le sol – CANTIS. Nos résultats ont montré que les deux modèles ont surestimé la minéralisation du C et n’ont pas prédit correctement la minéralisation du N des deux mélanges. Cette interaction antagoniste pour les mélanges a pu être corrigée par l’application d’un facteur de contact dans CANTIS, qui reflète la diminution de la biodisponibilité du C et du N, due à des hétérogénéités de distribution à une échelle fine du sol. Dans un deuxième temps, nous avons effectué des essais au champ (en condition réelles) pour suivre à la fois la décomposition de la paille de canne à sucre en mélange avec des fertilisants organiques et les émissions de GES. La quantité de paille décomposée a été proportionnelle à la quantité initiale laissée et n’a été affectée ni par la quantité de paille initiale, ni par le type de fertilisant apporté. Cette proportionnalité est transposable aux potentialités de stockage de carbone dans le sol et devrait être considérée lors de la mise en place de programmes de séquestration de carbone dans le sol ou lors de l’exportation de la paille pour une utilisation par ailleurs. Le type de fertilisant a un rôle clef sur les émissions de GES à court terme après la fertilisation. Les flux d’émissions moyens de CO2 et de N2O les plus élevés ont été obtenus en appliquant du lisier de porc, qui a une forte teneur en eau et est riche en N minéral. A l’inverse, les cinétiques des émissions de GES des fertilisants solides ont été régis par des facteurs environnementaux, dont certains pourraient être contrôlés, tels que l'apport en eau ou la quantité de fertilisant. L’utilisation de fertilisants organiques est bénéfique lorsqu’ils sont riches en N organique et pauvres en teneur en eau, comme la boue de station d’épuration sèche, mais la minéralisation de l’azote dans ce cas est progressive et nécessite l’élaboration de plans d’épandage spécifiques pour répondre aux besoins des culturesIn the current environmental context, it is crucial to optimize the use of resources to reduce waste and greenhouse gas (GHG) emissions. Renewable resources use and recycling lies at the heart of the circular economy model, in which a waste is a mobilizable, transformable, reusable and therefore renewable resource. In agriculture, the “virtuous circle” of circular economy can be achieved through the recycling of organic wastes as fertilizer and the adoption of an agroecological approach that favors ecosystem services for pest control, soil protection and carbon stocks increase, one of the examples of which is mulching. In sugarcane cropping systems straw left on the soil surface is also increasingly coveted by industrial sector to produce second-generation agrofuels. The emerging competition for biomass use and the underlying environmental issues make it necessary to assess both, the agronomic and the environmental advantages and disadvantages of joint recycling of sugarcane mulch and organic fertilizers. Therefore, the objectives of this work are i) to compare the effect of fertilizers of contrasting physicochemical quality, on the decomposition of a sugarcane mulch, and ii) to evaluate the potential of GHG emissions from mulch-fertilizer mixtures, according to the quantity of straw left and the quality of the fertilizers applied. The research strategy adopted in a first step aimed to detect carbon/nitrogen interactions during the combined recycling of straw and organic fertilizers. We have thus tested the predictability of the mineralization dynamics of C and N of the organic materials alone, or in mixture (straw/fertilizer) in the laboratory, by a simple additive model, and a mechanistic model of carbon and nitrogen transformation in the soil - CANTIS. Our results showed that both models overestimated the C mineralization and did not correctly predict the N mineralization of the mixtures. This antagonistic interaction for the mixtures was corrected by the application of a contact factor in CANTIS, which reflects the bioavailability decrease of C and N, due to distribution heterogeneities at a fine scale within the soil. In a second step, we conducted field trials (under real conditions) to measure both the decomposition of sugarcane straw mixed with organic fertilizers and GHG emissions. The amount of straw decomposed was proportional to the initial amount left and was affected neither by the amount of straw nor the type of fertilizer provided. This proportionality is transposable to the potential for carbon sequestration in the soil and should be considered when setting up carbon sequestration or when exporting the straw for alternative use. The type of fertilizer plays a key role in GHG emissions in the short term after fertilization. The highest average CO2 and N2O emission fluxes were obtained by applying pig slurry, which has a high water content and is rich in mineral N. Conversely, the kinetics of GHG emissions from solid fertilizers have been governed by environmental factors, some of which could be controlled, such as water intake or fertilizer quantity application. The use of organic fertilizers is beneficial when they are rich in organic N and poor in water content, such as dry sewage sludge, but the mineralization of nitrogen in this case is gradual and requires elaboration of a specific application strategies to meet crop needs. A better integration of the interactions between the different N and C sources should be considered, in order to develop modeling as a precise tool for the management of an agroecosystem
3
Langenbruch, Christina. "Effects of nutrient cycling through litter of different broadleaved deciduous tree species on soil biochemical properties and the dynamics of carbon and nitrogen in soil." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F1C2-F.
Full text
4
Ferreira, Ademir de Oliveira. "COMPARTIMENTOS DA MATÉRIA ORGÂNICA DO SOLO COMO INDICADORES DO SEQÜESTRO DE CARBONO EM SISTEMA PLANTIO DIRETO DE LONGA DURAÇÃO." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2009. http://tede2.uepg.br/jspui/handle/prefix/2199.
Full textAbstract:
Made available in DSpace on 2017-07-25T19:29:43Z (GMT). No. of bitstreams: 1
Ademir Oliveira Ferreira.pdf: 1294842 bytes, checksum: 8d7036f6aefa0cf3c549b0c63029e109 (MD5)
Previous issue date: 2009-07-13Decrease in soil organic carbon (SOC) content of the surface layer into deeper layers indicates the occurrence of the stratification in the profile due to continuous C addition of crop residues enriching the soil surface layer. The objective of this study was: in Chapter 3 the relationship of stratification (RE) of C of the soil organic matter (SOM) pools can be an indicator of C sequestration in no-tillage soils? In the chapter 4 the tensile strength of aggregates is affected by the C content of Pedosequence of Latosol with medium and clay texture? in Chapter 5 which is the C balance and the amount of crop residue needed to maintain a stable C balance in a Latosol with a medium and clay texture? The experimental design was a completely randomized 2x2x2 factorial with 12 treatments. Treatments consisted of: a) an Oxisol (Red Latosol) with medium and clayey texture, b) two soil sampling periods (T1 and T2) with one year interval between them, and c) two soil sampling depths (0-5 and 5-20 cm). The soil attributes assessed were: the separation of water stable aggregates classes (19-8, 8-4, 4-2, 2-1, 1-0,5 and 05-0,25 mm), particulate organic carbon (POC), total particulate nitrogen (TPN) in the aggregate classes. Also was determined total organic carbon (TOC) and total nitrogen (NT) in the whole sample and in the aggregates sizes classes and tensile strength of aggregates. The relationship of stratification was calculated by dividing the TOC and TN values of 0-5 cm layer by the values of the same attributes of 5-20 cm layer. The C sequestration rate and the stratification ratio changes were calculated by the difference between the T2 values minus T1. The tensile strength was measured in soil aggregates and assessed in 1920 aggregates for each sampling time. Also TOC and NT content were measured in aggregates. The aggregates greater than 8 mm represented more than 70 of the total mass in both the clay and in sandy soil. The relationship of stratification ratio (0-5:5-20 cm) of SOC, TN, POC and TPN soil indicated the improvement of the surface layer. A significant linear relationship between the SR and C sequestration rate in both textural classes showed an increase in C sequestration and was more evident in LV with medium texture. The increase in TOC content resulted in decreased tensile strength (TS) of the aggregates and was more evident in the 0-5 cm layer. The TS showed inverse relationship with the soil density and was higher in the LV medium texture. The rate of sequestration of C was 0.86 for the LV with medium texture and 0.76 Mg ha-1 for the clay texture and to maintain the stable balance of C is required an input of 8.6 Mg ha-1 of crop residues. The results presented confirm the hypothesis of SR to be a sensitive indicator for the rate of carbon sequestration in no-tillage soil. Key-words: Carbon stock, Carbon balance, Carbon sequestration, Soil management systems, particulate organic carbon, particulate nitrogen.
A redução no conteúdo de carbono (C) da camada superficial em direção as camadas mais profundas do solo indica a formação da estratificação no perfil devido à adição contínua de C pelos resíduos orgânicos resultando no enriquecendo a camada superficial do solo. O objetivo deste trabalho foi avaliar os seguintes assuntos: a) a relação de estratificação (RE) de C dos compartimentos da matéria orgânica do solo (MOS) pode ser um indicador do seqüestro de C no sistema plantio direto. b) a resistência tênsil dos gregados pode ser afetada pelo conteúdo de C em Pedossequencia de Latossolo com textura média e argilosa. c) o balanço de C e a quantidade de resíduos culturais necessária para manter o equilíbrio estável de C em um Latossolo com textura média e argilosa. O delineamento experimental foi um fatorial 2x2x2 inteiramente casualizado com 12 tratamentos. Os tratamentos constituíram-se de: a) um Latossolo Vermelho com textura média e argilosa, duas épocas de amostragem do solo (E1 e E2) com um ano de intervalo entre si e duas profundidades de amostragem (0-5 e 5-20 cm). Os atributos avaliados foram: a separação das classes de agregados do tamisamento úmido (19-8, 8-4, 4-2, 2-1, 1-0,5 e 05-0,25 mm), o carbono orgânico particulado (COP), o nitrogênio total particulado (NTP) nas classes de agregado, o C orgânico total (COT) e o nitrogênio total (NT) na amostra integral e nas classes de agregados e a resistência tênsil dos agregados. A relação de estratificação (RE) foi calculada dividindo-se o valor de COT e NT da camada de 0-5 cm pelo valor na camada 5-20 cm. A taxa de seqüestro de C e a variação da relação de estratificação foram calculadas através da diferença (D) entre os valores da E2 menos o da E1. A resistência tênsil (RT) do solo foi avaliada em 1920 agregados de cada época de coleta, determinando-se, também o conteúdo de COT e NT. A classe de agregado > 8 mm representou mais de 70% da massa dos agregados tanto na textura argilosa como na arenosa. Da mesma forma, o conteúdo de COT e NT foram maiores na classe de agregado > do que 4 mm comparado as demais classes nas duas classes texturais. A relação de estratificação 5:5-20 cm) de COT, NT, COP e NTP do solo indicou a melhoria da qualidade do solo da camada superficial. A relação linear e significativa entre o DRE com a taxa de seqüestro de carbono nas duas classes texturais mostrou o aumento no seqüestro de C e foi mais evidente no LV com textura média. O incremento do conteúdo de COT resultou na diminuição da resistência tênsil (RT) dos agregados e foi mais evidente na camada de 0-5 cm. A RT apresentou relação inversa com a densidade do solo e foi superior no LV textura média. A taxa de seqüestro de C foi de 0,86 para o LV textura média e 0,76 Mg ha-1 para o textura argilosa e para manter o equilíbrio estável de C é necessário o aporte de 8,6 Mg ha-1 de resíduos culturais. Os resultados apresentados confirmaram a hipótese da RE ser um indicador sensível para a taxa de seqüestro de carbono no solo em um sistema sob plantio direto consolidado.
5
Juice, Stephanie. "The Environmental Microbiome In A Changing World: Microbial Processes And Biogeochemistry." ScholarWorks @ UVM, 2020. https://scholarworks.uvm.edu/graddis/1181.
Full textAbstract:
Climate change can alter ecosystem processes and organismal phenology through both long-term, gradual changes and alteration of disturbance regimes. Because microbes mediate decomposition, and therefore the initial stages of nutrient cycling, soil biogeochemical responses to climate change will be driven by microbial responses to changes in temperature, precipitation, and pulsed climatic events. Improving projections of soil ecological and biogeochemical responses to climate change effects therefore requires greater knowledge of microbial contributions to decomposition. This dissertation examines soil microbial and biogeochemical responses to the long-term and punctuated effects of climate change, as well as improvement to decomposition models following addition of microbial parameters.
First, through a climate change mesocosm experiment on two soils, I determined that biogeochemical losses due to warming and snow reduction vary across soil types. Additionally, the length of time with soil microbial activity during plant dormancy increased under warming, and in some cases decreased following snow reduction. Asynchrony length was positively related to carbon and nitrogen loss. Next, I examined soil enzyme activity, carbon and nitrogen biodegradability, and fungal abundance in response to ice storms, an extreme event projected to occur more frequently under climate change in the northeastern United States. Enzyme activity response to ice storm treatments varied by both target nutrient and, for nitrogen, soil horizon. Soil horizons often experienced opposite response of enzyme activity to ice storm treatments, and increasing ice storm frequency also altered the direction of the microbial response. Mid-levels of ice storm treatment additionally increased fungal hyphal abundance. Finally, I added explicit microbial parameters to a global decomposition model that previously incorporated climate and litter quality. The best mass loss model simply added microbial flows between litter quality pools, and addition of a microbial biomass and products pool also improved model performance compared to the traditional implicit microbial model.
Collectively, these results illustrate the importance of soil characteristics to the biogeochemical and microbial response to both gradual climate change effects and extreme events. Furthermore, they show that large-scale decomposition models can be improved by adding microbial parameters. This information is relevant to the effects of climate change and microbial activity on biogeochemical cycles.
6
Manlay, Raphael. "Organic matter dynamics in mixed-farming systems of the West African savanna: a village case study from south Senegal." Diss., Institute of Forestry, Agricultural and Environmental Engineering (ENGREF), 2000. http://hdl.handle.net/10919/71623.
Full textAbstract:
Organic matter (OM) is a multi-purpose tool in West African smallholder mixed-farming systems, but its supply has been decreasing for several decades. To assess the viability of a mixed-farming system of south Senegal, carbon (C), nitrogen (N) and phosphorus (P; available in soil and noted POD) budgets (stocks and flows) were thus quantified.The village territory of the study showed a ring-like organisation with growing intensification of fertilization and cropping practices from the periphery (bush ring) to the compounds (compound fields).Stocks in plant and soil averaged 54.7 tC, 2.63 tN and 43.5 kgP ha 1 in old fallows. They were 97, 29 and 251 % higher than in the bush cropped fields, plant biomass accounting for nearly all of the rise. C, N and P amounts recorded in the soil of compound fields were higher than those of the bush field, but the increase was restricted mainly to the 0 10 cm layer. However, the rather weak response of local sandy soils to management can be interpreted only by reassessing the bio-thermodynamical signification of soil organic carbon cycling in the maintenance of the integrity of local agroecosystems.Manageable stocks of the whole village territory were estimated to 29.7 tC, 1.52 tN and 28.6 kgP ha 1 in 1997. Carbon was stored mainly in soil. Livestock, crop harvest and wood collecting were responsible for respectively 59, 27 and 14 % of the C uptake on the village territory. As a result, large C flows were set towards the compound ring (3.8 tC ha 1 y 1). N and P depletion of the system amounted to 4 kgN and 1 kgP ha 1 y 1, suggesting that the system was close to nutrient balance.Under current demographic growth rate, C depletion may reach 0.38 tC ha 1 y 1 and C demand may double during the next three decades. Without any intensification of farming practices, the viability of the system might soon be called into question.
7
Durigan, Mariana Regina. "Mudanças nos estoques de carbono e nitrogênio do solo em função da conversão do uso da terra no Pará." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-03062013-093119/.
Full textAbstract:
A atividade de mudança do uso da terra na Amazônia vem sendo apontada como principal fonte de CO2 para a atmosfera em função das emissões de C e N provenientes do solo. A prática de manejo adotada pode influenciar significativamente nos estoques de C e N do solo funcionando como dreno ou fonte de C e N para a atmosfera. Além disso, podem ser alterados: a fertilidade e a densidade do solo bem como as frações e a origem da MOS. Com o objetivo de avaliar o impacto das mudanças de uso da terra na região leste da Amazônia foram coletadas amostras de terra nos principais usos da terra na região de Santarém-PA, em três profundidades: 0-10, 10-20 e 20-30 cm. Através das amostras foi realizada a caracterização físico-química das áreas e foram determinados os teores de C e N do solo e os isótopos ? 13C e ? 15N com a finalidade de quantificar os estoques de C e N do solo e avaliar a dinâmica e origem da MOS. Para um subconjunto de amostras foi realizado o fracionamento físico da MOS e a determinação do C da biomassa microbiana para compreender como a mudança de uso da terra interferiu nessas frações. Somado a essas determinações foi realizada a estimativa dos fatores de emissão com base na metodologia descrita pelo IPCC. Através da caracterização físicoquímica as áreas de estudo são caracterizadas por solos argilosos a muito argilosos. Os maiores valores de pH, macronutrientes, CTC, SB e V% foram observados nas áreas de agricultura (AGR) sugerindo que a utilização de práticas como adubação e calagem, são capazes de alterar os padrões de fertilidade do solo na Amazônia, aumentando seus índices de fertilidade. Para os estoques de C e N pode-se dizer que a mudança de uso da terra na região estudada está contribuindo para as perdas de C e N do solo, principalmente quando a conversão é realizada para áreas de agricultura (AGR) e pastagem (PA) sendo que os estoques de C observados na camada de 0-30 cm nessas áreas foram 49,21 Mg C ha-1 (PA) e 48,60 Mg C ha-1 (AGR). O maior valor de ? 13C foi encontrado nas áreas de pastagens, -25,08?, sugerindo que para as áreas de PA existe diluição isotópica e que parte do C do solo ainda é remanescente da floresta. As frações da MOS apresentaram alterações na quantidade de C e na proporção das frações leve e oclusa, principalmente nos usos AGR e PA. A fração lábil da MOS (C da biomassa microbiana) também apresentou grande diferença entre os usos FLO e AGR (526,21 e 296,78 ?g g-1de solo seco), indicando que a AGR foi o uso que mais alterou os estoques de C e N do solo e também as frações da MOS. Os fatores de emissão calculados confirmam todos os resultados observados em relação a conversão de FLO para AGR, sendo que para esse uso o fator de emissão foi de 0,93 ± 0,033, sendo então o uso que mais emitiu C. Com base nos resultados conclui-se que a introdução de áreas agrícolas na região de Santarém, é a principal causa de perda de C e N do solo e consequentemente é o uso que mais contribui com as emissões de gases do efeito estufa.The land use change in the Brazilian Amazon has been identified as the main source of CO2 to the atmosphere due to emissions of soil carbon and nitrogenl. The management practice adopted can strongly influence the soil C and N stocks and may works like a sink or source of C and N to the atmosphere. Furthermore, can be changed: the soil fertility and bulk density as well as the SOM fractions and C source of the SOM. With the objective of evaluate the impact of the land use change in eastern Amazonia soil samples were collected in the main land uses in Santarém region, Para State of Brazil, at three depths: 0-10, 10-20 and 20-30 cm. Through the samples was performed the physicochemical characterization of the areas and were determined the soil C and N contents as well the isotopes ? 13C and ? 15N in order to quantify the soil C and N stocks and understand the SOM dynamics and evaluate the SOM origin. For a subset of samples were performed the physical fractionation of SOM and the determination of microbial biomass C to understand how the land use change may interfere in these fractions. Added to these determinations were estimated the emission factors based on the methodology described by the IPCC. Through the physicochemical characterization study areas can be characterized as a clayey loamy soils. The highest values of pH, macronutrients, CEC , sum of bases and base saturation were observed in croplands (CP), suggesting that the use of practices such as fertilization and liming are able to change the soil fertility patterns in the Amazon, increasing their fertility. For C and N stocks can be said that the land use change in the study area is contributing to the loss of soil C and N, especially when the conversion is done for croplands (CP) and grasslands (GS) areas and the value observed for soil C stocks in the 0-30 cm layer in these areas were 49.21 Mg C ha-1 (GS) and 48.60 Mg C ha-1 (CP). The highest ? 13C value was found in GS, -25.08 ?, suggesting that for these areas is occurring an isotope dilution and that part of the soil C is still remaining from forest. The SOM fractions showed changes in the amount of C and in the proportion of light and occluded fractions, especially in the uses CP and GS. The labile SOM fractions (microbial biomass) also showed a large difference between the UF and CP uses (526.21 and 296.78 mg g-1 of dry soil), indicating that CP affects the soil C and N stocks and also the SOM fractions. The emission factors calculated confirm all results observed for the conversion of UF for CP, and for this use the emission factor was 0.93 ± 0.033, and then this was the use that emitted more C. Based on the results we conclude that the introduction of croplands in Santarem region is the main cause of soil C and N loss and consequently contributes more to the greenhouse gases emission.
8
Truong, Van Vinh. "Carbon stocks and fluxes in tropical mangrove (Southern Vietnam)." Thesis, Nouvelle Calédonie, 2018. http://www.theses.fr/2018NCAL0002.
Full textAbstract:
Les forêts de mangrove contribuent de manière significative au flux d'énergie, au cycle des nutriments et du carbone dans l'océan côtier, étant un puits pour le CO2 atmosphérique. Les forêts de mangroves sont très productives et stockent une quantité élevée de carbone à la fois dans leurs sols et dans leur biomasse.Au cours de la décomposition de la litière, les nutriments et le carbone peuvent être recyclés ou exportés vers les écosystèmes adjacents par l'action des marées. La mangrove de Can Gio (Ho Chi Minh Ville, Vietnam), dégradée par l'épandage de défoliants pendant la guerre du Vietnam, a pu être restaurée grâce à la replantation et à la régénération naturelle. À ce jour, la forêt de mangrove de Can Gio est la plus grande forêt de mangrove contiguë au Vietnam, et est devenue la première réserve biosphère UNESCO dans ce pays. L'objectif principal de cette thèse était de caractériser le cycle du carbone dans la forêt de mangrove tropicale.Les résultats de cette thèse ont permis de:- Développer des équations allométriques permettant d’estimer la biomasse aérienne de la forêt plantée de mangroves de l’espèceRhizophora apiculatadans le sud du Vietnam;- Calculer les stocks de carbone totaux dans différents peuplements de mangrove se développant sous le climat tropical du sud du Vietnam;- Caractériser les taux de décomposition de la litière et évaluer la dynamique des nutriments et des métaux traces au cours des processus de dégradation de la litière, ainsi que l'évolution de δ13C pendant la décomposition;- Déterminer la variabilité saisonnière des flux de CO2 à différentes interfaces: sol-air, eau-air et tronc-air, et caractériser les profils de concentration en CO2 dans la canopéeMangrove forests significantly contribute to energy flow, nutrient and carbon cycling in the coastal ocean, being a sink for atmospheric CO2. Mangroves forests are highly productive and store high amount of carbon both in their soils and in their biomass. During leaf litter decomposition, nutrients and carbon can be recycled or exported to adjacent ecosystems by the tidal action. Can Gio mangrove, degraded by the spraying of defoliants during the Vietnam War, successfully recovered through replantation and natural regeneration after 40 years. To date, the Can Gio mangrove forest is the largest contiguous mangrove forest in Vietnam, and became the first Mangrove Biosphere Reserve in this country. The main objective of this PhD thesis was to characterize carbon cycling within the Can Gio mangrove forest, which is a tropical one.The results of this PhD thesis allowed to: - Develop allometric equations and to estimate the aboveground biomass of Rhizophora apiculata Blume planted mangroves forest in Southern Vietnam; - Calculate the total carbon stocks in different mangrove stands developing under the tropical climate of Southern Vietnam; - Characterize the leaf litter decomposition rates, and assess nutrients and trace metals dynamics during litter decay processes, as well as the evolution of δ13C during decay; - Determine the seasonal variability CO2 fluxes at different interfaces: soil-air, water-air and trunk-air, and to characterize CO2 concentrations profiles in the canopy
9
Wang, Eugenia. "Growth of nitrogen-containing carbon nanofibers." Connect to resource, 2006. http://hdl.handle.net/1811/6446.
Full textAbstract:
Thesis (Honors)--Ohio State University, 2006.Title from first page of PDF file. Document formatted into pages: contains 55 p.; also includes graphics. Includes bibliographical references (p. 51). Available online via Ohio State University's Knowledge Bank.
10
Burch, Hilary Jane. "Bioapplications of nitrogen-doped carbon nanotubes." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437176.
Full text
11
Liang, Jianglin, and 梁江林. "Ruthenium-catalyzed carbon-nitrogen bond formations." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31245729.
Full text
12
Shiao, Jeansong. "Properties of diamondlike carbon and nitrogen containing diamondlike carbon films." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1056992626.
Full text
13
Zhang, Min. "Study on selective carbon-carbon, carbon-nitrogen, and carbon-oxygen bonds formation starting from alkynes." Rennes 1, 2009. http://www.theses.fr/2009REN1S036.
Full textAbstract:
The thesis is composed of two parts. Part I presents catalytic C-C, C-N, C-O bond formation: a series of dienylethers, 2,5-disubstituted furans, allylketones, γ-functionalized ketones, multisubstituted quinolines were made starting from terminal alkynes with the initial help of a ruthenium catalyst. Part II presents C-C, C-N, C-O bond formation reactions: a variety of tetrahydropyrimidines, and 1,3-oxazines were synthesized starting from electron-deficient alkynes via multiple component reactionsLa thèse est composée de deux parties. La partie I présente la formation catalytique de liaisons C-C, C-N et C-O : une série d’ethers, de diényle, furanes 2,5-disubstitués, cétones allyliques et γ-fonctionalisées et quinolines polysubstituées ont été préparées à partir d’alcynes avec l’aide initiale d’un catalyseur de ruthenium. La partie II présente la formation de liaisons C-C, C-N, C-O: une variété de tetrahydropyridines, et de 1,3-oxazines ont été synthétisées à partir d’alcynes electrophiles via des réactions à composants multiples
14
Ye, Yuxuan Ph D. Massachusetts Institute of Technology. "Development of new transition metal-catalyzed carbon-fluorine, carbon-nitrogen, and carbon-carbon bond forming processes." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118281.
Full textAbstract:
Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references.
Chapter 1. Palladium-Catalyzed Fluorination of Cyclic Vinyl Triflates: Dramatic Effect of TESCF₃ as an Additive A method for the synthesis of cyclic vinyl fluorides with high levels of regiochemical fidelity has been achieved by Pd-catalysis employing a new biarylphosphine ligand and TESCF₃ as a crucial additive. Five, six, and seven-membered vinyl triflate substrates, as well as a few acyclic substrates undergo the transformation successfully. The intriguing "TESCF₃ effect" provided a new tool for addressing the problem of the formation of regioisomers in Pd-catalyzed fluorination reactions. Chapter 2. Mechanistic Studies on Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification by TESC₃ as an additive. A detailed mechanistic hypothesis for the Pd-catalyzed fluorination of cyclic vinyl triflates, and the unusual effect of TESCF₃ as an additive has been developed by combined experimental and computational studies. The preference of conducting [beta]-hydrogen elimination rather than reductive elimination from the trans-LPd(vinyl)F complex, which is generated predominantly due to the trans-effect, caused the poor regioselectivity of the fluorination reaction under TESCF₃-free conditions. An in situ ligand modification by trifluoromethyl anion, leading to the generation of the cis-LPd(vinyl)F complex which prefers reductive elimination rather than Phydrogen elimination, is proposed to be responsible for the improved regioselectivity of the fluorination reaction when TESCF₃ was used as an additive. Chapter 3. CuH-Catalyzed Enantioselective Alkylation of Indoles with Ligand-Controlled Regiodivergence A method for the enantioselective synthesis of either NI- and C3-chiral indoles by CuH-catalysis, depending on the choice of ligand, was developed. In contrast to conventional indole functionalization in which indoles are used as nucleophiles, hydroxyindole derivatives are employed as electrophiles in this method. DFT calculations indicated that the extent to which the Cu-P bonds of the alkylcopper intermediate distort, determines the regioselectivity of the reaction.
by Yuxuan Ye.
Ph. D. in Organic Chemistry
15
Schubert, Maria. "Carbon partitioning in nitrogen fixing root nodules." Doctoral thesis, [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=96736597X.
Full text
16
Pozo, Alejandro del. "Carbon/nitrogen relations in cereals and legumes." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317269.
Full text
17
TASAYCO, CARLOS MANUEL SANCHEZ. "NITROGEN INCORPORATION INTO AMORPHOUS FLUORINATED CARBON FILMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=3698@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOAs propriedades tribológicas de revestimentos de carbono usados em discos rígidos magnéticos foram de enorme importância para o contínuo aumento da densidade de informação armazenada nos mesmos. As características mecânicas e estruturais de filmes de carbono amorfo também foram indispensáveis para o desenvolvimento de revestimentos que atendessem às especificações do desenvolvimento destes dispositivos: alta dureza e densidade, além de baixo coeficiente de atrito e alta resistência ao desgaste. Neste trabalho são apresentados os efeitos da incorporação de nitrogênio em filmes de carbono fluorado (a-C:H:F) depositados pela técnica de deposição por vapor químico assistido por plasma. As propriedades mecânicas e estruturais foram investigadas com o uso das técnicas nucleares (retroespalhamento Rutherford, detecção de recuo elástico, reação nuclear), espectroscopia de fotoelétrons induzidos por raios-X, medidas de tensão interna (por perfilometria), espectroscopia de absorção no infravermelho, espectroscopia Raman, microscopia de força atômica e medidas de ângulo de contato. Foi depositada uma série de filmes onde foi variada a pressão de N2 em uma atmosfera precursora de CH4-CF4 (1:2) (PN2 = 0% até 60%). A tensão de autopolarização foi fixada em - 350V. Os resultados obtidos mostram que as propriedades dos filmes são controladas pela incorporação de nitrogênio que chega a 20 at.%. Identificou-se um decaimento na taxa de deposição com o incremento da pressão parcial de N2, e um sensível decaimento na concentração de flúor. O filme fica menos tensionado, o que pode resultar em uma melhoria na adesão. Entretanto, o ângulo de contato diminui, resultando em um aumento no coeficiente de atrito. Novos estudos procurando aumentar simultaneamente as concentrações de F e N são sugeridos.
The tribological properties of carbon coatings of hard magnetic disks played an important role for the continuous increase of their storage capacity. The mechanical and structural properties were also important: high density, hardness and wear resistance, and low friction coefficient. In this work, we study the effects of the nitrogen incorporation into fluorinated carbon films (a-C:H:F) deposited by plasma enhanced chemical vapor deposition. The film properties were investigated by using a multitechnique approach: nuclear techniques (Rutherford backscattering, elastic recoil and nuclear reaction analyses), x-ray photoelectron spectroscopy, internal stress measurements by perfilometry, Raman and Infrared spectroscopies, atomic force microscopy and contact angle measurements. Films were deposited changing the N2 partial pressure in a precursor atmosphere also composed by a fixed CH4-CF4 mixture (1:2) (PN2: 0 - 60%), with the self-bias voltage of -350V. The results show that the film properties are controlled by the nitrogen incorporation, with an important fluorine content reduction. The internal stress reduction may result in an increase of the film adhesion. However, the contact angle decreases upon nitrogen incorporation, resulting in an increase of the friction coefficient. New studies with the goal of obtain a simultaneous increase of both fluorine and nitrogen content are suggested.
18
Kivimäki, Sanna Katariina. "Changes in carbon and nitrogen dynamics in Sphagnum capillifolium under enhanced nitrogen deposition." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5728.
Full textAbstract:
Peatland ecosystems only cover 2-3 % of the Earth‟s surface but they represent significant carbon stores, holding approximately one third of the global soil carbon (C). The major peat forming genera Sphagnum appears to be highly sensitive to increased N availability. Many studies have shown decreased productivity of Sphagnum which could lead to a decrease in the amount of C stored, especially as many studies also show an increase in the decomposition rate with higher N deposition. However, the overall effects of N on CO2 fluxes of Sphagnum remain unclear. The present study aimed to look at the effects of increased N on Sphagnum productivity, decomposition and CO2 fluxes after long-term N additions (> 5 years) using a field experiment at Whim Moss in southern Scotland where N deposition has been manipulated employing a very realistic application coupled to rainfall since 2002. The experiment also has treatments with PK addition to test the effects of removing P and/or K-limitation. Measurements of plant tissue nutrient concentrations, visual assessments of Sphagnum viability, and pore water analysis were also carried out. Nitrogen additions increased tissue N, and decreased Sphagnum shoot extension and productivity. Simultaneous P and K additions alleviated the effects of N on tissue N concentrations and growth, although this was only significant for shoot extension. Visual assessments correlated well with tissue chemistry and productivity; the decline in health was associated with high %N and reduced productivity. Interestingly, in the present study increased N decreased the mass loss and again when PK was added with N decomposition rates were more similar to the control. With respect to the carbon balance of the site and the sustainability of peatlands the results suggest that the negative effect of N on C assimilation may be partially offset by the reduced decomposition rates. The CO2 measurements showed a large loss of C as CO2 from all the Sphagnum plots which was exacerbated by adding N especially when the air temperature increased. The positive temperature response of ecosystem respiration with N additions suggests that in high N deposition areas climate change and subsequent temperature rises will increase C losses from bogs.
19
Mohammed, Askia Musah. "Biomass, carbon, nutrient stocks and litter decomposition in Ghanain cocoa ecosystems." Thesis, University of Reading, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625496.
Full textAbstract:
This study recognised the quantification of biomass, C and nutrient stocks in cocoa systems of Ghana as an important step to producing a sustainable and carbon-friendly cocoa sector. Eight farms in Ghana were selected for sampling cocoa stands on the basis of three variables: region (Eastern region (ER), Western region (WR)), shade management (shaded, un shaded) and stand age «15, >15 years). All biometric data were collected within a plot area of 2700 m2 in each farm. Also two experiments, a l20-day dry matter loss and a l30-day carbon emission from litter decomposition and organic matter mineralization, were conducted concurrently. In these, single species leaf litters: cocoa (as in unshaded cocoa system), Newbouldia laevis (dominant shade tree in Eastern region) and Persea americana (dominant shade tree in Western region) and I: I mixed species leaf litters (mimicking shaded systems: cocoa + Newbouldia laevis and cocoa + Persea americana) were incubated to determine and predict the litter decomposition and nutrient dynamics in cocoa systems with or without the shade trees. Allometric equations were developed to estimate the biomass of live cocoa tree components (R2 = 0.79 - 0.95). Biomass of non-cocoa trees was estimated using an existing allometric equation developed by the Food and Agricultural Organization. In addition, the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model was tested on hypothetical cocoa systems to assess its suitability to simulate biomass, C and nutrient stocks in the systems over time. Total ecosystem biomass ranged from 48.1 ± 6.5 to 101.6 ± 12.6 Mg I ha. The unshaded system had the lowest biomass production. Biomass production was higher in the Eastern than Western region and larger in > 15 years stands than < 15 years stands. While the C stock in biomass from shaded systems was twice that in unshaded systems, there was no significant difference in total ecosystem C stocks (biomass C + soil C to 60 cm depth) between the two systems due to a larger soil carbon stock in the latter.
20
Kingham, Rachel. "The broad-scale impacts of livestock grazing on saltmarsh carbon stocks." Thesis, Bangor University, 2013. https://research.bangor.ac.uk/portal/en/theses/the-broadscale-impacts-of-livestock-grazing-on-saltmarsh-carbon-stocks(a81ba92d-ac40-49c4-ba93-982bffb077d9).html.
Full textAbstract:
In light of recent upward trends in atmospheric carbon dioxide concentration, efforts have turned to methods of sequestering atmospheric carbon into other stable carbon sinks. Enhancing carbon sequestration by natural systems is an effective way of managing carbon sequestration. Due to high productivity and high sedimentation rates, salt marshes are extremely efficient at capturing and storing carbon, and provide the ideal environment for enhancing carbon sequestration rates through the management of livestock grazing, a common use of salt marshes. However, salt marshes are subject to a range of environmental stressors, which can vary considerably over a large spatial scale . It is therefore important to understand the implications of environmental and contextual variability on the use of livestock grazing as a carbon management tool. Twenty-two salt marshes were selected along the coasts of north Wales and north-west England to assess the impact of grazers on above and below-ground carbon stocks and processes in relation to broader contextual variables. The impacts of seasonality on carbon sequestration rates were also assessed by investigating a salt marsh carbon budget over the course of one year. Grazing was found to have a negative impact on several above-ground plant characteristics, but no impact on soil carbon stocks or overall carbon sequestration rates. Instead, below-ground processes were explained more by the broader environmental variables and seasonal changes. While this study does not discount the fact that grazing may affect soil carbon stocks on the small-scale, or after initial introduction, it shows that grazing impacts are insignificant relative to broader contextual factors on marshes with wellestablished grazing regimes.
21
Heidorn, Christina Melanie. "Soil carbon dynamics in a nitrogen-enriched grassland." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0028/MQ50343.pdf.
Full text
22
Ince, Christopher Paul. "Investigations into palladium-catalysed carbon-nitrogen bond formation." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392496.
Full text
23
Abualghaith, Abdulaziz. "Carbon and nitrogen metabolisn in orchid-mycorrhiza associations." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604555.
Full textAbstract:
Members of the Orchidales produce dust seeds so lacking in nutrient and carbon reserves that they are dependent upon appropriate fungal partners to supply the essential additional carbon and nutrients required for successful establishment in nature. These plants are thus initially mycoheterotrophic before they normally go on to develop green leaves and become autotrophic as adults. However, at least 210 species of orchid remain fully mycoheterotrophic into adulthood. The metabolic pathways involved in the nitrogen and carbon fluxes from fungus-to -plant in mycoheteratrophic are still poorly understood, but result in characteristic enrichment in 13C and 13N. In this thesis in vitro studies on agar are employed to investigate the effects of different N sources, with and without sugar or cellulose carbon sources on the heterotrophic growth of mycorrhizal orchid seedlings and metabolite pools in the plants and their fungal partners. It is hypothesised that glutamine, a central metabolite in assimilation of mineral by basidiomycete fungi, passes from fungus-to -plant as in traditional models of N assimilation by ectomycorrhizal plants. A range of nitrogen and carbon sources including isotopically labelled 14C and 13C-glucose together with 15N labelled N sources including nitrate, ammonium, ammonium nitrate, glutamine, glycine and arginine were supplied to orchid mycorrhizal fungi in pure culture and to mycorrhizal seedlings of Goodyera repens or Dactylorhiza fuchsii. In three compartment Petri dishes in which the seedlings were grown with their fungal partners colonising the two other compartments, simultaneous additions of DC and 15N tracers provided compelling evidence of fungal assimilatory pathways providing co-transport of C and N into heterotrophic seedlings of G. repens. Nitrate was a better N source than ammonium or amino acids for the plants, and metabolomic analysis showed strong up-regulation of relative abundance of glutamine in the fastest growing plants. The findings presented in this thesis provides strong circumstantial evidence that glutamine serves as a major combined N and C source transported from fungus-to-plant in heterotrophic orchid seedlings.
24
Alvarado, Adriana Delgado. "Interactions between carbon and nitrogen metabolism in legumes." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274992.
Full text
25
Lewis, Jason Douglas. "Carbon, nitrogen, and water fluxes from turfgrass ecosystems." Diss., Kansas State University, 2010. http://hdl.handle.net/2097/4376.
Full textAbstract:
Doctor of PhilosophyDepartment of Horticulture, Forestry, and Recreation Resources
Dale J. Bremer
Turfgrass covers 1.9% of the nation’s surface area and is the largest irrigated crop in the USA. Developed urbanized land is projected to double by 2025, which will increase turf’s environmental impact. Studies were conducted to evaluate environmental impacts by characterizing nitrogen, carbon, and water fluxes in turfgrass ecosystems. Emissions of nitrous oxide (N[subscript]2O), a major greenhouse gas and ozone depleter were measured from bermudagrass (Cynodon dactylon L. Pers. x C. transvaalensis Burtt-Davy) (bermuda), perennial ryegrass, (Lolium perenne L.) (rye), and zoysiagrass, (Zoysia japonica Steud.) (zoysia) under regional N management. In a separate study, N2O fluxes were measured from bermuda fertilized with controlled-release N fertilizers including polymer-coated and organic-N, and quick release urea. Emissions of N2O were measured using static surface chambers and gas chromatography. Zoysia, with less N requirements, had lower emissions than bermuda. Cumulative N[subscript]2O emissions were similar among N types. To measure water and carbon fluxes, a portable non-steady state chamber was designed and tested. The chamber had minimal affects to the canopy during field measurements: leak values averaged <1.5 micromol CO[subscript]2 m[superscript]-2 s[superscript]-1; average chamber pressure was 0.09 Pa ±0.01 Pa; temperature rise inside the chamber averaged 0.74C; and the chamber had 90% photosynthetically active radiation transmittance. Using the chamber, differences were detected in net photosynthesis (Pnet), gross photosynthesis (Pg), evapotranspiration (ET), canopy stomatal conductance (gc), and water use efficiency (WUE) in well-watered tall fescue (Festuca arundinacea Schreb.), Kentucky bluegrass (Poa pratensis L.) (KBG), zoysia, and bermuda. Irrigation requirements, visual quality ratings, and genetic rooting potential of 28 KBG cultivars and 2 Texas bluegrass hybrids (P. pratensis x P. arachnifera Torr.) were quantified in greenhouse and rainout facility studies. Average water applied ranged from 23.4 to 40.0 cm among cultivars. Bedazzled, Preakness, and Bartitia required less water and had higher average quality than other cultivars. Compact America and Mid-Atlantic phenotypes exhibited greatest potential for success in integrating reduced water inputs with maintenance of acceptable visual quality. Results indicated that turfgrass management could mitigate N[subscript]2O emissions and conserve water while maintaining healthy turfgrass, and the new chamber will enhance turfgrass studies by providing rapid measurements of photosynthesis.
26
Chaichana, Saisiri. "Dissolved organic carbon and nitrogen in coastal waters." Thesis, University of East Anglia, 2017. https://ueaeprints.uea.ac.uk/62312/.
Full textAbstract:
Dissolved organic matter (DOM) including carbon and nitrogen (DOC and DON) are important but poorly understood components of the marine biogeochemical cycle. In this study, the distribution and cycling of DOC and DON, and particulate organic carbon and nitrogen (POC and PON) were investigated in North Sea surface and bottom water during the stratified summer season in 2011 and 2012, along with other key biogeochemical parameters such as nutrients. The summer DOC, DON, POC and PON ranged from 32.7-134.5, 2.8-13.7, 1.1-43.8 and 0.3-5.9 μM, respectively. The well-mixed water of the southern North Sea was also surveyed in the winter of 2011; measured concentration of DOC and DON were 56.2-224.8 and 3.7-12.3 μM. In summer, DOM and POM generally exhibited high levels in the southern well-mixed water (SM), whereas inorganic nutrient concentrations were higher in the northern bottom water (NB) due to nutrient regeneration and offshore water inflow. DOM in summer and inorganic nutrients in winter were also clearly influenced by riverine inputs. DON was the dominant nitrogen fraction of northern surface water and SM in summer, while in NB, TOxN (nitrate + nitrite) was the dominant fraction. Analysis of SmartBuoy samples show phytoplankton provided a net source of DOM over the spring bloom period with net degradation in autumn and winter. Incubation experiments on water collected from two North Sea sites in autumn, winter 2013 and spring 2014 showed no nutrient (N and P) limitation on DOM degradation. The experiments yield mean bacterial decay rate constants (for three seasons) at the two sites of 4 ± 8 and 2 ± 3 %d-1 kDOC and 3 ± 4 and 4 ± 4 %d-1 kDON, under dark conditions. In comparison to the Redfield ratio, the bulk C:N molar ratio is enriched in carbon relative to nitrogen, while the slope C:N ratio is close to the Redfield ratio, but with a background of high C:N material.
27
Mori-Quiroz, Luis Martin. "Transition metal catalyzed Carbon-nitrogen bond forming reactions." Revista de Química, 2015. http://repositorio.pucp.edu.pe/index/handle/123456789/101381.
Full textAbstract:
Las reacciones de formación de enlaces carbono-nitrógeno (C–N) son transformaciones fundamentales en la naturaleza y también procesos básicos para la preparación de moléculas y materiales relevantes a las actividades humanas. El desarrollo de reacciones nuevas y eficientes para la formación de enlaces C–N es, por lo tanto, de gran interés en los ámbitos académico e industrial. El progreso logrado en los últimos 20 años se ha enfocado, principalmente, en procesos de formación de enlaces Csp2–N; sin embargo, hay una creciente gama de reacciones catalizadas por metales de transición que permite la introducción de nitrógeno en estructuras alquílicas (formación de enlaces Csp3–N). Este artículo describe una selección de métodos catalíticos modernos para la formación de enlaces C–N.Carbon-nitrogen (C–N) bond forming reactions are fundamental transformations in nature and also basic processes for the preparation of molecules and materials relevant to human activities. The development of new and efficient reactions for the formation of C–N bonds are therefore of great interest in academic and industrial settings. Progress in the last 20 years has focused mainly in Csp2–N bond forming processes; however, there is growing range of transition metal catalyzed reactions for the introduction of nitrogen in alkyl frameworks (Csp3–N bond formation). This article describes a selection of modern catalytic methods for the formation of C–N bonds.
28
Curtis-Summers, Shirley. "Stable Isotopes of Carbon and Nitrogen and Diet." Society of Antiquaries of Scotland, 2016. http://hdl.handle.net/10454/17856.
Full text
29
Chizari, Kambiz. "Synthesis of nitrogen-doped carbon nanotubes : catalytic applications." Strasbourg, 2011. http://www.theses.fr/2011STRA6047.
Full textAbstract:
Depuis la découverte des nanotubes de carbone (CNT) en 1991, beaucoup d'efforts ont été faits afin de connaître leurs propriétés intrinsèques et les applications possibles. Une des méthodes les plus efficaces, utilisée pour modifier ses propriétés physiques et chimiques, est le dopage de CNT à l'azote ou le bore. L’objectif de ce travail est de réaliser la synthèse de nanotubes de carbone dopés à l’azote (N-CNT) et d'étudier les performances catalytiques de ce matériau soit en tant que support de catalyseur soit directement comme catalyseur. L'influence des différents paramètres de synthèse sur les propriétés des N-CNT a été étudiée. Par la suite, les N-CNT ont été utilisés comme support de catalyseur pour l'hydrogénation du cinnamaldéhyde et leurs performances catalytiques ont été comparées à celles des CNT non-dopés. Il a été montré que les N-CNT synthétisés dans des conditions différentes présentent différentes performances catalytiques. Les N-CNT ont également été utilisés en tant que catalyseur pour l'oxydation sélective de l'H2S en soufre élémentaire et les résultats sont discutés dans cette thèse. Enfin, les études réalisées avec les nanotubes de carbone ont été transposées sur un matériau nouveau et prometteur qu’est le graphène et/ou graphène multi-couche. Nous avons dans un premier temps synthétisé ce matériau à partir de graphite expansé en utilisant les irradiations micro-ondes, puis une étude préliminaire a également été faite sur le dopage à l’azote de ce matériau par un traitement aux micro-ondes du graphite expansé dispersé dans de l'hydroxyde d'ammonium. Le FLG est utilisé dans ce travail comme support de catalyseur pour la réaction d'hydrogénation du cinnamaldéhyde et ses performances catalytiques sont comparées à d'autres catalyseurs supportés sur des supports tels que le graphite naturel, le graphite expansé et les nanotubes de carboneSince the discovery of carbon nanotubes (CNT) in 1991, a lot of efforts have been done in order to find out their intrinsic properties and their possible applications. One of the most efficient methods used for tuning its physical and chemical properties is doping CNTs by nitrogen or boron. The aim of this work deals with the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) and with the study of the catalytic performance of this material either as catalyst support or as a metal-free catalyst. The influence of the different synthesis parameters on the physical and chemical properties of the N-CNTs was investigated. Afterwards, the N-CNTs were used as catalyst support for the hydrogenation of cinnamaldehyde and its catalytic performance was compared to that obtained on the undoped CNTs. It was shown that N-CNTs synthesized in different conditions lead to different catalytic performances which was mainly linked with the nature of the incorporated nitrogen species. The N-CNTs were also employed as a metal-free catalyst for the selective oxidation of H2S into elemental sulfur and the results are discussed within this thesis. Recently 2D carbon material, namely graphene, has received a great interest due to its special physical properties. The previous investigations on the other graphitic material such as carbon nanotubes facilitate the understanding of the properties and behavior of this material. In this thesis we also worked on the synthesis of the few-layer graphene (FLG), using microwave irradiations. A preliminary study has also done on the nitrogen-doping of this material by microwave treatment on the expanded graphite dispersed in ammonium hydroxide. The FLGs were used as a catalyst support for the hydrogenation of cinnamaldehyde and its catalytic performance is compared to other graphitic materials such as natural graphite, expanded graphite and carbon nanotubes
30
Ning, Xue. "Carbon molecular sieve membranes for nitrogen/methane separation." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53986.
Full textAbstract:
Nitrogen-selective Carbon Molecular Sieve (CMS) membranes were developed for nitrogen/methane separation. Effects of pyrolysis conditions including pyrolysis temperature protocol and pyrolysis atmosphere were studied for Matrimid® and 6FDA:BPDA-DAM precursors. It was revealed that high pyrolysis temperature is essential to achieve attractive nitrogen/methane selectivity due to the subtle size difference between the two gas penetrants. Detailed study on one of the best performing CMS membranes showed that diffusion selection, more specifically, the entropic factor responsible for diffusion selection provides a significant contribution to the high selectivity. The effect of precursor was studied by considering nine carefully selected polymers. The structures and properties of these polymer precursors were compared and correlated with the separation performance of resulting CMS membranes. The translation of intrinsic CMS transport properties into the hollow fiber morphology was also explored. Substructure collapse and asymmetry lost during pyrolysis were observed, which resulted in significant increases of separation layer thickness and decreases in permeance. Vinyltrimethoxy silane (VTMS)-treatment was applied to polymer hollow fiber before pyrolysis to overcome the problem of substructure collapse. The effects of VTMS-treatment on both the substructure and skin layer are discussed.
31
Neary, Erika L., Daniel G. Neary, Steven T. Overby, and Sally M. Haase. "Prescribed Fire Impacts on Soil Carbon and Nitrogen." Arizona-Nevada Academy of Science, 2002. http://hdl.handle.net/10150/296593.
Full text
32
Krause, Caitlin Joy. "Evaluating the toxicity of nitrogen-functionalized carbon nanotubes." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/4667.
Full text
33
Patenauden, Geneviève. "Quantifying forest carbon stocks and changes in support of the Kyoto Protocol." Thesis, University of Oxford, 2006. https://ora.ox.ac.uk/objects/uuid:0d69355d-db71-45a6-b0e7-7f9673f1118b.
Full textAbstract:
This thesis brings together research conducted on field based, remote sensing and modelling approaches to meet reporting requirements set by the Kyoto Protocol. Parties are given the option to meet part of their greenhouse gases reduction requirements through the conservation and enhancement of the carbon stored in forest ecosystems. Two contrasting forests (Monks Wood, UK, 52°24' N, 0°14' W and Thetford UK, 52°30' N, 0°30' E) were selected for the development and assessment of the selected methods. Field-based measurements were used to quantify carbon stocks in Monks Wood, providing the first exhaustive assessment of the carbon content held in a UK semi-natural woodland. The total carbon content of the stands varied from 346 to 616 tonnes per hectare (t ha-1) and highlighted the importance of broadleaved woodlands as carbon stores in the UK. A quantitative appraisal of remote sensing methods was also provided. For land cover discrimination, both optical and radar remote sensing have been successful. For forest carbon stock estimation, LiDAR approaches may provide the only viable remote sensing tool for this purpose. As a result, a LiDAR-based method was developed and the results compared to field-based estimates. At the stand level, the agreement between the field-based and the LiDAR estimates was r=0.85. At the woodland level, due to the enhanced capability of LiDAR to monitor the natural variability of carbon across the woodland, the estimates were nearly 24% lower than those from the ground. Remote sensing of field-based approaches are unsuitable alone for quantifying below-ground carbon content and can be resource intensive. Process-based models enable an estimation of below-ground components to be made. Much uncertainty however arises from the lack of information available on model parameter values. The 3-PG model was used to simulate forest production in Thetford forest and a Bayesian calibration was applied. The results showed that this statistical approach could provide an overall framework for integrating and quantifying the uncertainty in the combined field based, remote sensing and modelling datasets, a result highly relevant in the context of the Kyoto Protocol.
34
Tavallali, Leila. "Spatial and temporal variability of carbon stocks within the River Colne Estuary." Thesis, University of Essex, 2018. http://repository.essex.ac.uk/21405/.
Full textAbstract:
Saltmarshes are one of the most significant blue carbon sinks but there is a paucity of information regarding saltmarsh carbon stocks globally, consequently these habitats are not included in the global carbon budget. The aim of this study is therefore to better understand the spatial and temporal variation of saltmarsh sediment total organic carbon (TOC) content. Therefore, three saltmarshes along the salinity gradient of the Colne Estuary were studied. The effect of the study sites’ locations along the estuary, higher plant species distribution, above-ground biomass and aerobic respiration on TOC content was investigated. The spatial and temporal variation of sediment TOC content was investigated by monthly sampling from two habitats and three zones at each study site. There was a significant spatial variation in plant species distribution which could be due to zonation and the location of the sites along the estuary. Saltmarsh plants were the important driver of spatial and temporal variations in sediment TOC content. The sediment TOC content at the study sites in the lower (Colne Point) and the mid (Brightlingsea) estuary was significantly higher than the upper estuary (Wivenhoe) (P < 0.001, range: 9-25 Kg C m-2). The range of sediment TOC content of the studied saltmarshes was between 88% - 290% higher than other UK studied saltmarshes and between 4% -169% higher than the majority of the studied marshes in the Northern Hemisphere. Therefore, if the sediment carbon content of the similar saltmarshes to the Colne estuary were taken into account it would suggest that the UK and global saltmarsh sediment TOC estimate would increase. It will take possibly about 100 years for the realignment saltmarshes at Essex to reach the carbon storage capacity of Colne Point. Therefore, the Colne Point natural saltmarsh is a very significant carbon reservoir that has been overlooked.
35
Dou, Fugen. "Long-term tillage, cropping sequence, and nitrogen fertilization effects on soil carbon and nitrogen dynamics." Texas A&M University, 2006. http://hdl.handle.net/1969.1/3831.
Full textAbstract:
Management practices that may increase soil organic matter (SOM) storage include
conservation tillage, especially no till (NT), enhanced cropping intensity, and
fertilization. My objectives were to evaluate management effects on labile [soil microbial
biomass (SMB) and mineralizable, particulate organic matter (POM), and hydrolyzable
SOM] and slow (mineral-associated and resistant organic) C and N pools and turnover in
continuous sorghum [Sorghum bicolor (L.) Moench.], wheat (Triticum aestivum L.), and
soybean [Glycine max (L.) Merr.], sorghum-wheat/soybean, and wheat/soybean
sequences under convent ional tillage (CT) and NT with and without N fertilization. A
Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochepts) in southern central
Texas was sampled at three depth increments to a 30-cm depth after wheat, sorghum, and
soybean harvesting. Soil organic C and total N showed similar responses to tillage,
cropping sequence, and N fertilization following wheat, sorghum, and soybean. Most
effects were observed in surface soils. NT significantly increased SOC. Nitrogen
fertilization significantly increased SOC only under NT. Compared to NT or N addition,
enhanced cropping intensity only slightly increased SOC. Estimates of C sequestration
rates under NT indicated that SOC would reach a new equilibrium after 20 yr or less of
imposition of this treatment. Labile pools were all significantly greater with NT than CT
at 0 to 5 cm and decreased with depth. SMB, mineralizable C and N, POM, and
hydrolyzable C were highly correlated with each other and SOC, but their slopes were
significantly different, being lowest in mineralizable C and highest in hydrolyzable C.
These results indicated that different methods determined various fractions of total SOC.
Results from soil physical fractionation and 13C concentrations further supported these
observations. Carbon turnover rates increased in the sequence: ROC < silt- and clayassociated
C < microaggregate-C < POM-C. Long-term incubation showed that 4 to 5%
of SOC was in active pools with mean residence time (MRT) of about 50 days, 50% of
SOC was in slow pools with an average MRT of 12 years, and the remainder was in
resistant pools with an assumed MRT of over 500 years.
36
Crook, Hannah D. "Carbon and nitrogen cycling in upland wetlands : impacts of changing climate and atmospheric nitrogen deposition." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412169.
Full text
37
Sandoval, Rojano Stefania. "Functionalization of carbon nanomaterials with nitrogen, halides and oxides." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/394000.
Full textAbstract:
Los materiales compuestos por grafeno y nanotubos de carbono (CNTs) han despertado un amplio interés debido a sus propiedades excepcionales. La variación de éstas, empleando diversas técnicas de modificación aumentan sus aplicaciones potenciales en muchos campos.
Ésta tesis describe la funcionalización de nanomateriales de carbono con nitrógeno y diversos haluros y óxidos. La modificación de la estructura de nanotubos de carbono multicapa (MWCNTs) y derivados de grafeno se llevó a cabo mediante reacciones sólido-gas y sólido-líquido. Hemos empleado diferentes métodos de funcionalización, que incluyen oxidación, funcionalización con nitrógeno y dopaje, así como modificaciones de las cavidades internas y superficies externas de los nanotubos de carbono, para modular las propiedades de las nanoestructuras preparadas. Mediante un estudio sistemático de las condiciones de tratamiento y una exhaustiva caracterización se determinaron las características estructurales de las muestras y se evaluaron algunas de sus propiedades fisicoquímicas.
En ésta tesis proponemos un método simple, eficiente y reproducible para la síntesis de óxido de grafeno reducido (RGO) modificado con nitrógeno. La naturaleza de los átomos de nitrógeno dentro de la red del RGO se ha modulado mediante tratamientos de amonolísis de óxido de grafeno (GO) a temperaturas comprendidas entre 25 ˚C y 800 ˚C. El protocolo propuesto permite tanto la introducción de grupos funcionales alifáticos (funcionalización con N) como la de nitrógeno estructural (dopaje con N). Adicionalmente, la composición estructural de las muestras funcionalizadas y dopadas con nitrógeno se modificó mediante tratamientos posteriores empleando altas temperaturas y atmosferas no oxidantes. Éstos tratamientos provocan rearreglos internos que confieren mayor estabilidad térmica a los materiales.
Por otro lado, se llevó a cabo el llenado de las cavidades y la decoración de las superficies externas de los MWCNTs con compuestos inorgánicos. Reportamos la formación de nanotubos inorgánicos monocapa dentro de los nanotubos de carbon empleando una técnica de capilaridad del material laminar en su fase fundida. Además, mediante la optimización de los parámetros experimentales conseguimos favorecer el crecimiento de éstos sistemas inorgánicos monocapa con respecto la formación de otras nanoestructuras, tales como, nanopartículas, nanobarras y nanoserpientes de los halogenuros empleados. Hemos descrito una nueva técnica para el aislamiento ó liberación de las sustancias previamente introducidas en las cavidades de los MWCNTs. Así, exploramos el uso potencial de los fulerenos como agentes aisladores o promotores de la liberación de estructuras huéspedes.
Finalmente, hemos preparado MWCNTs decorados con óxidos de titanio reducidos empleando tratamientos a altas temperaturas. Mediante la oxidación de los nanotubos se obtuvieron “nanocollares” de titania libres de carbono. Los materiales soportados presentan una actividad fotocatalítica superior a la del material de referencia titania P25.Graphene and carbon nanotubes (CNTs) are of wide interest in materials science due to their outstanding properties. Several approaches allow modulating their properties further expanding their potential applications in many fields. This thesis reports on the functionalization of carbon nanomaterials with nitrogen, halides and oxides. The modification of the structure of multiwalled carbon nanotubes (MWCNTs) and graphene derivatives has been carried out through solid-gas and solid-liquid reactions. Different methods of functionalization, which include oxidation, nitrogen functionalization and doping, as well as endohedral and exohedral modifications have been employed for tuning the properties of the prepared nanostructures. A systematic study of the conditions of treatment and an extensive characterization has allowed the determination of the structural characteristics of the samples and the evaluation of some of their physical and chemical properties. In this thesis we propose a simple, efficient and reproducible method for the synthesis of nitrogen-containing reduced graphene oxide (RGO). The nature of the nitrogen atoms within the RGO lattice has been tuned by ammonolysis treatments of graphene oxide (GO) in the range of 25 ˚C-800 ˚C. The reported protocol allows the introduction of aliphatic moieties (N-functionalization) and structural nitrogen (N-doping). Additionally, the structural composition of the N-containing RGO has been modified by post-annealing the material under non-oxidizing atmospheres. High temperature treatments induce internal rearrangements, leading to samples with an enhanced thermal stability. On the other hand, endohedral and exohedral functionalization of MWCNTs with inorganic materials have been carried out. We report on the formation of single-layered inorganic nanotubes within the cavities of MWCNTs through a molten phase capillary wetting technique. We have optimized the conditions of the synthesis to enhance the growth of the single-layered nanotubes, while decreasing the formation of other nanostructures (nanoparticles, nanorods and nanosnakes). A new technique for the confinement and/or release of the filled substances within the hollow cavity of the CNTs has also been developed. We have explored the potential of fullerenes as corking agents and as promoting species for the release of guest structures. Finally, we have prepared MWCNTs decorated with reduced titanium oxides employing high temperature treatments. By oxidation of MWCNTs self-standing titania “nano-necklaces” are formed. The photocatalytic performance of the carbon supported materials overpasses that of the reference material titania P25.
38
Rajab, T. M. A. "Studies on carbon metabolism and nitrogen fixation by Gloeothece." Thesis, Swansea University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638610.
Full textAbstract:
When cultures of Gloeothece grown under constant light, were transferred to dark anerobic conditions, the rate of acetylene reduction dropped within 1h to 25-30% of that in the light, and reached a minimum after 10-12h. The only source at ATP for nitrogenase, under such conditions, is substrate level phosphorylation utilising endogenous material. All attempts to support N2-fixation by an exogenous source of energy proved unsuccessful. Although Gloeothecewas able to fix nitrogen under dark anaerobic conditions, no nitrogenase synthesis was observed. Gloeothece survived under dark anaerobic conditions for at least 96h, but they appeared to lose the ability to protect nitrogenase against inactivation by O2 over this period. Thus, when cultures of Gloeothece maintained under dark anaerobic conditions for more than 12h, were transferred to the light under anaerobic conditions, the nitrogenase activity which subsequently appeared was oxygen-sensitive. ATP is a necessary source of energy for N2-fixation. On the other hand, ADP inhibits nitrogenase activity. Therefore, the relative amounts of ADP and ATP may control nitrogenase activity. A routine method for measuring adenine nucleotides in Gloeothece, based on the luciferin-luciferase technique, was developed as existing methodology was found unsuitable. Under constant illumination, the observed fluctuations in nitrogenase activity in Gloeothece were not found to be related to changes in the ADP/ATP ratio. However, the ADP/ATP ratio had an indirect effect, possibly via synthesis, on the nitrogenase activity in Gloeothece grown under an alternating cycle of 12h light and 12h darkness. On the other hand, acetylene reduction was inversely related to the ADP/ATP ratio when cultures of Gloeothece were transferred from dark anaerobic conditions to dark aerobic and then to light aerobic conditions.
39
Tan, M. Md. "Aspects of carbon, nitrogen and sulphur diagenesis in sediments." Thesis, University of East Anglia, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353295.
Full text
40
Lodwig, Emma Mary. "Regulation of carbon and nitrogen metabolism in Rhizobium leguminosarum." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368874.
Full text
41
Newton, Jason. "A carbon and nitrogen isotope study of CO3 chondrites." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259887.
Full text
42
Cavan, Graeme Patrick. "Interaction of carbon and nitrogen metabolism in Schizosaccharomyces pombe." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259573.
Full text
43
Tundel, Rachel E. (Rachel Elizabeth). "Advances in palladium-catalyzed carbon-nitrogen bond forming processes." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36283.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.Vita. Leaf 68 blank.
Includes bibliographical references.
Chapter 1. Microwave-assisted, palladium-catalyzed C-N bond-forming reactions with aryl/heteroaryl nonaflates/halides and amines using the soluble amine bases DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) or MTBD (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) and a catalyst system consisting of Pd2dba3 and ligands (XantPhos, 2-dicylcohexylphosphino-2',4',6'-triisopropyl-1,1 '-biphenyl (XPhos) and 2-di-tert-butylphosphino-2',4',6'-triisopropyl-1, '-biphenyl) resulted in good to excellent yields of arylamines in short reaction times. Chapter 2. Using a catalyst comprised of the bulky, electron-rich monophosphine ligand di-tert-Butyl XPhos (2-di-tert-butylphosphino-2',4',6'-triisopropyl-1,1'-biphenyl) and Pd2dba3 with sodium tert-butoxide as the base, amino heterocycles were coupled successfully with aryl/heteroaryl halides in moderate to excellent yields.
by Rachel E. Tundel.
S.B.
44
Clark, D. R. "Carbon-nitrogen stress, and the growth of marine phytoplankton." Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636260.
Full textAbstract:
A number of phytoplankton species from a range of taxa (including diatoms, dinoflagellates and prymnesiophytes) were grown in batch cultures in closed systems at four dissolved inorganic carbon concentrations. Cultures were supplied with NO3- or NH4+ and growth was limited by C and/or N. Response of the phytoplantkon to C and/or N stress was investigated with measurements including C:N ratios, cell C, N and chl.a quotas, chl.a:C ratios and the internal amino acid pool. Responses to C-limitation included an increase in cell N and chl.a quota, chl.a:C ration and the gln:glu ratio. Responses to increased N-limitation included an increase in the cell C-quota and C:N ratio, together with decreases in cell-N and chl.a quota, chl.a:C ratio, and the gln:glu ratio. Generally indications of N-stress were greater when the N-source was NO3- rather than NH4+ as demonstrated at the level of the cell C, N and chl.a quotas, and at the level of internal amino acid pool, although none of these indicators were found to be consistent for every species. A study of the kinetics of DIC utilisation revealed that to a greater or lesser extent, the utilisation of NO3- relative to NH4+ consistently resulted in a significant decrease in the carbon specific growth rate of all species investigated. The expression of extracellular carbonic anhydrase may endow marine phytoplankton with a competitive advantage, regardless of cell size or motility, while large and chain forming species appeared to be at a relative disadvantage with respect to the kinetics of DIC utilisation. Typically, the species investigated attained a KG for dissolved inorganic carbon of <300 μM. The results of the study suggest that DIC rate limitation of phytoplankton growth may be of minor consequence in the marine environment.
45
Rennie, Anthony. "Nitrogen-enriched carbon materials for high-power electrochemical capacitors." Thesis, University of Strathclyde, 2011. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16769.
Full text
46
Marsay, Christopher Matthew. "Particulate trace metals, carbon and nitrogen in the Mesopelagic." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/351794/.
Full text
47
Li, Jinling. "Effects of Biosolids on Carbon Sequestration and Nitrogen Cycling." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/49585.
Full textAbstract:
Land application of biosolids has been demonstrated to improve nutrient availability (mainly N and P) and improve organic matter in soils, but the effects of biosolids on C sequestration and N cycling in the Mid-Atlantic region is not well understood. The objectives were: 1) to investigate soil C sequestration at sites with a long-term history of biosolids either in repeated application or single large application; 2) to characterize and compare soil C chemistry using advanced 13C nuclear magnetic resonance (NMR) and C (1s) near edge x-ray absorption fine structure (NEXAFS) spectroscopic techniques; and 3) to compare biosolids types and tillage practices on short-term N availability in the Coastal Plain soils. Biosolids led to C accumulation in the soil surface (< 15 cm) after long-time application in both Piedmont and Coastal Plain soils. The C saturation phenomenon occurred in Coastal Plain soils, thus additional soil C accumulation was not achieved by increasing C inputs from biosolids to the Coastal Plain. Soil organic C from profiles in the field sites was not different at depths below the plow layer (15-60 cm). The quantitative NMR analyses concluded that O-alkyl C was the dominant form in the particulate organic matter (POM), followed by aromatic C, alkyl C, COO/N-C=O, aromatic C-O, OCH3 / NCH and ketones and aldehydes. The aliphatic C and aromatic C were enriched but the O-alkyl C was decreased in the biosolids-amended soils. The changes indicated that the biosolids-derived soil C was more decomposed and, thus, more stable than the control. The NEXAFS spectra showed that O-alkyl C was the dominant form in the POM extracted from biosolids-amended soils, followed by aromatic C, alkyl C, carboxylic C and phenolic C groups. These results were similar to those from NMR analysis. The regression and correlation analyses of C functional groups in the POM between NEXAFS and NMR indicated that both techniques had good sensitivity for the characterization of C from biosolids-amended soils. To evaluate short-term biosolids N availability, a three-year field study to investigate the effects of lime-stabilized (LS) and anaerobically digested (AD) biosolids on N availability in a corn-soybean rotation under conventional tillage and no-tillage practices was set up in 2009-2011. Results showed that both LS and AD biosolids increased spring soil nitrate N, plant tissue N at silking, post-season corn stalk nitrate N, grain yield, and soil total N by the end of the growing season. The same factors used to calculate plant available N for incorporated biosolids can be used on biosolids applied to no-till systems in coarse-textured soils. All these results indicated that the application of biosolids affects the long-term quantification and qualification of soil organic C and also improve short-term N availability in the Mid-Atlantic region.Ph. D.
48
Ogbu, Chidiebere, and Gregory Dr Bishop. "Peroxide Sensing Using Nitrogen-Doped Screen-Printed Carbon Electrodes." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/asrf/2019/schedule/93.
Full textAbstract:
Nitrogen-doped carbon materials such as carbon nanotubes and graphene have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (e.g. oxygen reduction) and biosensing (e.g. hydrogen peroxide reduction). Electrocatalytic properties of these materials have been attributed to enhanced electron transfer ability exhibited by surface nitrogen atoms compared to typical carbon structures. Screen-printing has been widely employed in the production of low-cost carbon-based electrodes for sensors and biosensors. Here, we develop nitrogen-doped screen-printed carbon (N-SPCE) electrodes for detection of hydrogen peroxide - an important analyte in biosensing. Conductive ink was formulated in the lab from nitrogen-doped graphite that was produced using a simple urea-based soft nitriding technique. N-SPCEs exhibited electrocatalytic activity towards hydrogen peroxide reduction, while SPCEs prepared from unmodified carbon showed no ability to electrocatalytically reduce H2O2. Amperometric detection of H2O2 using N-SPCEs at an applied potential of -0.4 V (vs. Ag/AgCl) displayed a wide linear range of 20 µM to 5.3 mM, and a low limit of detection (2.4 µM). These performance characteristics compare favorably to other electrodes for H2O2 sensing and indicate that the low-cost, easy-to-prepare N-SPCEs described here are promising platforms for the development of biosensors.
49
Dezi, Silvia <1974>. "Modelling the effects of nitrogen deposition and carbon dioxide enrichment on forest carbon balance." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3362/.
Full textAbstract:
Atmospheric CO2 concentration ([CO2]) has increased over the last 250 years, mainly due to human activities. Of total anthropogenic emissions, almost 31% has been sequestered by the terrestrial biosphere. A considerable contribution to this sink comes from temperate and boreal forest ecosystems of the northern hemisphere, which contain a large amount of carbon (C) stored as biomass and soil organic matter. Several potential drivers for this forest C sequestration have been proposed, including increasing atmospheric [CO2], temperature, nitrogen (N) deposition and changes in management practices. However, it is not known which of these drivers are most important.
The overall aim of this thesis project was to develop a simple ecosystem model which explicitly incorporates our best understanding of the mechanisms by which these drivers affect forest C storage, and to use this model to investigate the sensitivity of the forest ecosystem to these drivers.
I firstly developed a version of the Generic Decomposition and Yield (G’DAY) model to explicitly investigate the mechanisms leading to forest C sequestration following N deposition. Specifically, I modified the G’DAY model to include advances in understanding of C allocation, canopy N uptake, and leaf trait relationships. I also incorporated a simple forest management practice subroutine. Secondly, I investigated the effect of CO2 fertilization on forest productivity with relation to the soil N availability feedback. I modified the model to allow it to simulate short-term responses of deciduous forests to environmental drivers, and applied it to data from a large-scale forest Free-Air CO2 Enrichment (FACE) experiment. Finally, I used the model to investigate the combined effects of recent observed changes in atmospheric [CO2], N deposition, and climate on a European forest stand.
The model developed in my thesis project was an effective tool for analysis of effects of environmental drivers on forest ecosystem C storage. Key results from model simulations include: (i) N availability has a major role in forest ecosystem C sequestration; (ii) atmospheric N deposition is an important driver of N availability on short and long time-scales; (iii) rising temperature increases C storage by enhancing soil N availability and (iv) increasing [CO2] significantly affects forest growth and C storage only when N availability is not limiting.
50
Harris, Wylie Neal. "Grassland carbon and nitrogen dynamics: effects of seasonal fire and clipping in a mixed-grass prairie of the southern great plains." Texas A&M University, 2003. http://hdl.handle.net/1969.1/3911.
Full textAbstract:
Plant production and soil microbial biomass (SMB) in grassland ecosystems are
linked by flows of carbon (C) and nitrogen (N) between the two groups of organisms. In
native mixed grasslands of the southern Great Plains, these cycles are strongly
influenced by climate. They may also be modulated by the timing and intensity of
disturbances such as fire and clipping. We assessed the relative influence of climate and
disturbance on plant community and soil C and N dynamics. Combined effects of fire
and clipping were assessed in a 2x3 factorial design including spring fire and light
clipping or continuous clipping. Seasonal fire effects were evaluated in a one-way
analysis incorporating spring and fall fire in unclipped plots. Plant cover and biomass
(by functional type), litter mass, SMB C and N, soil density fraction concentration and
composition, soil organic C, total N, and inorganic N, soil temperature and moisture, soil
respiration, and net N mineralization were measured at monthly intervals. C4 grasses
were unaffected by fire or clipping, probably as a result of summer drought in both studyyears. Clipping reduced cover of C3 annual grasses but increased that of C3 perennials,
resulting in no net change in C3 grass biomass. Fire did not affect C3 grass cover or
biomass. Both fire and clipping reduced litter mass. This was reflected in seasonal
declines in SMB C in fire treatments, suggesting that the primary input of microbial C in
this ecosystem occurs by decomposition of current-season plant litter. Litter removal
offers a single mechanism by which fire-induced increases in soil temperature and
reductions in light soil density fraction concentration, soil moisture, and net N
mineralization rates may be explained. Lack of treatment effects on soil respiration rates
suggest that plant roots represent an important component of the plant-soil C cycle, not
quantified in this research. Overall, treatment effects were relatively minor compared to
seasonal climate-related changes in response variables, particularly in light of repeated
summer drought.