Dissertations / Theses on the topic 'Nitroge fixation'
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Li, Youzhong, and Youzhong Li@health gov au. "Respiration and nitrogen fixation by bacteroids from soybean root nodules : substrate transport and metabolism in relation to intracellular conditions." The Australian National University. Faculty of Science, 2003. http://thesis.anu.edu.au./public/adt-ANU20040630.114138.
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Bacteroids of B. japonicum from nodules of soybean roots were isolated using differential centrifugation (the standard bench method) and density gradient centrifugation methods (either sucrose- or Percoll-) under anaerobic conditions in which N2 fixation was preserved. The relationships between N2 fixation and respiration, O2 supply, O2 demand, substrate (mainly malate) transport and metabolism in bacteroids were investigated using the flow chamber system. In related experiments, the primary products of N2 fixation which leave the bacteroids were investigated using a 15N-labelling technique in a closed shaken system and other biochemical methods.¶
In the flow chamber experiments, the rates at which O2 was supplied to bacteroids in the chamber were varied by (a) changing the flow rate of reaction medium through the chamber; (b) by changing the [O2 free] in the inflowing reaction medium by using either 3-5% (v/v) or 100% air in the gas mixture above the stirred reaction medium in two reservoir flasks; (c) by successively withdrawing bacteroids from the chamber, thus increasing the supply of O2 per bacteroid to those remaining in the chamber. The results showed that the rate of O2 supply regulates respiratory demand for O2 by bacteroids rather than the O2 concentration present in the reaction system. Respiration is always coupled to N2 fixation. ¶
Uptake of malate by bacteroids withdrawn from the flow chamber was measured under microaerobic conditions. Malate uptake by these N2-fixing bacteroids was lower than that by bacteroids isolated under aerobic conditions, which eliminate N2 fixation of bacteroids, but is closely correlated with bacteroid respiration rates. When respiration was increased by an increase in O2 supply, malate uptake by bacteroids was also increased. This suggested that transport of malate through the bacteroid membrane is also regulated by O2 supply, but indirectly. Higher uptake by bacteroids under aerobic conditions was observed because respiration was enhanced by the high availability of O2, but the fast uptake of malate by bacteroids driven by the abnormal respiration rates may not reflect the reality of malate demand in vivo by bacteroids when N2 fixation by bacteroids is fully coupled. ¶
The results of 15N labelling experiments and other biochemical assays once again demonstrated that ammonia is the principal significant 15N labelled product of N2 fixation accumulated during 30 min in shaken assays with 0.008-0.01 atm O2. Alanine although sometimes found in low concentrations in the flow chamber reactions, was not labelled with 15N in shaken closed system experiments. No evidence could be obtained from the other biochemical assays, either. Therefore, it is concluded that these and earlier results were not due to contamination with host cytosolic enzymes as suggested by Waters et al. (Proc. Natl. Aca. Sci. 95, 1998, pp 12038-12042). ¶
Malate transported into bacteroids is oxidized in a modified TCA cycle present in bacteroids. The results of flow chamber experiments with a sucA mutant (lacking a-ketoglutarate dehydrogenase) showed that respiratory demand for O2 by the mutant bacteroids is regulated by O2 supply in the same way as the wild-type. Despite differences in other symbiotic properties, rates of nitrogen fixation by the mutant bacteroids, based on the bacteroid dry weight, appeared to be the same as in the wild-type. Also N2 fixation was closely coupled with respiration in the same manner in both mutant bacteroids and wild type bacteroids. These results and other supporting data, strongly support the conclusion that there is an alternative pathway of the TCA cycle in bacteroids, which enables the missing step in the mutant to be by-passed with sufficient activity to support metabolism of transported malate.
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Supeno. "Sonochemical fixation of nitrogen." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0016/MQ57783.pdf.
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Supeno, Carleton University Dissertation Chemistry. "Sonochemical fixation of nitrogen." Ottawa, 2000.
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Wätjen, Florian. "Rhenium and Osmium PNP Pincer Complexes for Nitrogen Fixation and Nitride Transfer." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0005-12D8-3.
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Klawonn, Isabell. "Marine nitrogen fixation : Cyanobacterial nitrogen fixation and the fate of new nitrogen in the Baltic Sea." Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-122080.
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Biogeochemical processes in the marine biosphere are important in global element cycling and greatly influence the gas composition of the Earth’s atmosphere. The nitrogen cycle is a key component of marine biogeochemical cycles. Nitrogen is an essential constituent of living organisms, but bioavailable nitrogen is often short in supply thus limiting primary production. The largest input of nitrogen to the marine environment is by N2-fixation, the transformation of inert N2 gas into bioavailable ammonium by a distinct group of microbes. Hence, N2-fixation bypasses nitrogen limitation and stimulates productivity in oligotrophic regions of the marine biosphere. Extensive blooms of N2-fixing cyanobacteria occur regularly during summer in the Baltic Sea. N2-fixation during these blooms adds several hundred kilotons of new nitrogen into the Baltic Proper, which is similar in magnitude to the annual nitrogen load by riverine discharge and more than twice the atmospheric nitrogen deposition in this area. N2-fixing cyanobacteria are therefore a critical constituent of nitrogen cycling in the Baltic Sea. In this thesis N2 fixation of common cyanobacteria in the Baltic Sea and the direct fate of newly fixed nitrogen in otherwise nitrogen-impoverished waters were investigated. Initially, the commonly used 15N-stable isotope assay for N2-fixation measurements was evaluated and optimized in terms of reliability and practicality (Paper I), and later applied for N2-fixation assessments (Paper II–IV). N2 fixation in surface waters of the Baltic Sea was restricted to large filamentous heterocystous cyanobacteria (Aphanizomenon sp., Nodularia spumigena, Dolichospermum spp.) and absent in smaller filamentous cyanobacteria such as Pseudanabaena sp., and unicellular and colonial picocyanobacteria (Paper II-III). Most of the N2-fixation in the Northern Baltic Proper was contributed by Aphanizomenon sp. due to its high abundance throughout the summer and similar rates of specific N2-fixation as Dolichospermum spp. and N. spumigena. Specific N2 fixation was substantially higher near the coast than in an offshore region (Paper II). Half of the fixed nitrogen was released as ammonium at the site near the coast and taken up by non-N2-fixing organisms including phototrophic and heterotrophic, prokaryotic and eukaryotic planktonic organisms. Newly fixed nitrogen was thereby rapidly turned-over in the nitrogen-depleted waters (Paper III). In colonies of N. spumigena even the potential for a complete nitrogen cycle condensed to a microcosm of a few millimeters could be demonstrated (Paper IV). Cyanobacterial colonies can therefore be hot-spots of nitrogen transformation processes potentially including nitrogen gain, recycling and loss processes. In conclusion, blooms of cyanobacteria are instrumental for productivity and CO2 sequestration in the Baltic Sea. These findings advance our understanding of biogeochemical cycles and ecosystem functioning in relation to cyanobacterial blooms in the Baltic Sea with relevance for both ecosystem-based management in the Baltic Sea, and N2-fixation and nitrogen cycling in the global ocean.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.
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Huang, Ying-Sheng. "Evidence for Multiple Functions of a Medicago Truncatula Transporter." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699903/.
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Legumes play an important role in agriculture as major food sources for humans and as feed for animals. Bioavailable nitrogen is a limiting nutrient for crop growth. Legumes are important because they can form a symbiotic relationship with soil bacteria called rhizobia that results in nitrogen-fixing root nodules. In this symbiosis, rhizobia provide nitrogen to the legumes and the legumes provide carbon sources to the rhizobia. The Medicago truncatula NPF1.7/NIP/LATD gene is essential for root nodule development and also for proper development of root architecture. Work in our lab on the MtNPF1.7/MtNIP/LATD gene has established that it encodes a nitrate transporter and strongly suggests it has another function. Mtnip-1/latd mutants have pleiotropic defects, which are only partially explained by defects in nitrate transport. MtNPF1.7/NIP/LATD is a member of the large and diverse NPF/NRT1(PTR) transporter family. NPF/NRT1(PTR) members have been shown to transport other compounds in addition to nitrate: nitrite, amino acids, di- and tri-peptides, dicarboxylates, auxin, abscisic acid and glucosinolates. In Arabidopsis thaliana, the AtNPF6.3/NRT1.1( CHL1) transporter was shown to transport auxin as well as nitrate. Atchl1 mutants have defects in root architecture, which may be explained by defects in auxin transport and/or nitrate sensing. Considering the pleiotropic phenotypes observed in Mtnip-1/latd mutant plants, it is possible that MtNPF1.7/NIP/LATD could have similar activity as AtNPF6.3/NRT1.1(CHL1). Experimental evidence shows that the MtNPF1.7/NIP/LATD gene is able to restore nitrate-absent responsiveness defects of the Atchl1-5 mutant. The constitutive expression of MtNPF1.7/NIP/LATD gene was able to partially, but not fully restore the wild-type phenotype in the Atchl1-5 mutant line in response to auxin and cytokinin. The constitutive expression of MtNPF1.7/NIP/LATD gene affects the lateral root density of wild-type Col-0 plants differently in response to IAA in the presence of high (1mM) or low (0.1 mM) nitrate. MtNPF1.7/NIP/LATD gene expression is not regulated by nitrate at the concentrations tested and MtNPF1.7/NIP/LATD does not regulate the nitrate-responsive MtNRT2.1 gene. Mtnip-1 plants have an abnormal gravitropic root response implicating an auxin defect. Together with these results, MtNPF1.7/NIP/LATD is associated with nitrate and auxin; however, it does not act in a homologous fashion as AtNPF6.3/NRT1.1(CHL1) does in A. thaliana.
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H, Boström Kjärstin. "Nitrogen fixation among marine bacterioplankton." Doctoral thesis, Högskolan i Kalmar, Naturvetenskapliga institutionen, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:hik:diva-24.
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While bacterioplankton indisputably control vital biogeochemical paths in the cycling of carbon and nutrients in the world’s oceans, our knowledge about the functional and genetic diversity of bacterioplankton communities is negligible. In this thesis, molecular and more traditional microbiological methods were used to study the specific function of N2-fixation and in a general sense diversity of marine bacterioplankton species. Most oceans are nitrogen limited and, therefore, adaptive to bacterioplankton capable of N2-fixation. Recent studies have found nifH genes (coding for the nitrogenase enzyme) related to diverse heterotrophic bacteria in oceanic seawater samples indicating that, along with cyanobacteria, also heterotrophic bacteria benefit from N2-fixation. Here, molecular and cultivation methods were used to examine diazotrophic bacterioplankton in the Baltic Sea. We successfully isolated heterotrophic N2-fixing bacteria belonging to the γ-proteobacterial class by means of low-nitrogen plates and semi-solid diazotrophic medium tubes. The isolates required low-O2 conditions for N2-fixation. Using Real-time PCR it was found that heterotrophic bacterioplankton carrying the nifH gene was abundant (3 x 104 nifH gene copies L seawater-1) at locations in the Southwest Baltic proper. With the aim to identify the main N2-fixing organisms in Baltic Proper surface waters, a clone library of nifH gene transcripts (RNA) was generated. Clone inserts were exclusively related to Aphanizomenon sp. and Nodularia sp. Using quantitative real-time PCR it was found that the nifH gene expression from Nodularia sp. was highly variable between stations in the Baltic Proper but was 10-fold higher during mid summer relative to early summer and fall. A diel study showed a 4-fold increase in Nodularia transcript concentrations at early to mid day relative to rest of the day. Real-time PCR was found to be a powerful and highly sensitive method for measuring gene expression. Since nucleic acids are a prerequisite for molecular analyses of bacterioplankton dynamics a protocol to extract DNA from seawater samples was developed with the aim to maximize the yield of high-quality DNA. Each step in the protocol was important for the efficiency of extraction. The obtained extraction efficiencies were up to 92% for seawater samples and up to 96% for isolates. The protocol provides a guideline for DNA extraction from seawater samples for other studies. In a global sampling campaign (9 locations from polar, tropical and temperate regions) we sampled DNA from surface water and constructed 16S rRNA gene libraries to investigate diversity and biogeography of bacterioplankton. Approx. 80% of the sequences found were similar to sequences already deposited in GenBank, indicating that a large fraction of the marine bacterioplankton already has been sampled, which in turn suggests a limited global bacterioplankton diversity. This thesis have improved our knowledge about the composition and nifH gene expression of the diazotrophic bacterioplankton community in the Baltic Sea and contribute significantly to the discussion on global marine bacterioplankton diversity and biogeography.Östersjön är ett av världens största brackvattensystem. Den ekologiska balansen i detta hav är hotad på grund av övergödning. Mycket arbete har därför fokuserats på att reducera utsläppen av näringsämnen, speciellt kväve. Dessa ansträngningar kan dock motverkas av bakterier som har förmåga att omvandla luftens kväve till metaboliskt användbart ammonium (kvävefixering). På sommaren är Östersjöns primärproduktion begränsad av kväve, med följden att det årligen uppstår massiva blomningar av kvävefixerande bakterier, framför allt cyanobakterier. Dessa är främst Aphanizomenon och Nodularia, men inte endast de fototrofa cyanobakterierna har förutsättningar att fixera N2. NifH gener (genen som kodar för nitrogenas) bärs också av heterotrofa bakterioplankton, vilket har visats i studier i främst Atlanten och Stilla havet. Med hjälp av två olika odlingsmetoder lyckades vi isolera heterotrofa kvävefixerande bakterier tillhörande klassen γ-proteobakteria från Östersjön. Svårigheten med att finna dessa bakterier ligger i att de kräver en miljö med mycket låg syrehalt för att kunna fixera kväve. Resultaten från denna studie ledde oss vidare till att undersöka vilka organismer som uttrycker nifH genen (och då troligen även fixerar kväve) i Östersjön. En av de bakterier som isolerats kunde påvisas med Realtids PCR i ett relativt stort antal (3 x 104 nifH genkopior per liter) vid en av de ursprungliga provtagningsstationerna. För att söka rätt på de olika organismtyper som uttrycker nifH skapades ett klonbibliotek baserat på mRNA extraherat från havsvatten. Det visade sig då att alla de närmare 100 kloner som sekvenserades tillhörde antingen Aphanizominon eller Nodularia. De heterotrofa bakteriernas nifH genuttryck var troligen i jämförelse med dessa cyanobakterier alltför lågt för att kunna detekteras. Realtids PCR mätningar av Nodularias nifH genuttryck visade på en stor variation mellan de olika provtagningsstationerna samt mellan de olika provtagningstillfällena. Vi fann dock en kraftig ökning under juli med en nedgång igen i augusti. En dygnscykelstudie visade att Nodularia nifH genuttrycket ökade under förmiddagen med en topp mitt på dagen för att sedan minska igen. Detta troligen med anledning av att den energikrävande kvävefixeringsprocessen sker under de ljusa timmarna då cellen får energi från fotosyntesen. I de molekylärbiologiska metoderna som används för att få information om identitet och aktivitet hos skilda organismer krävs att DNA och RNA kan extraheras från prover tagna i naturliga vattenmiljöer. Även om antalet bakterier tillsynes är högt, så är mängden DNA och RNA per liter havsvatten relativt låg, därför krävs ett väl fungerande protokoll för denna extraktion. I en inledande studie i denna avhandling optimerades en metod för att utvinna DNA. Ett antal sådana protokoll finns publicerade men dessa har ofta lågt utbyte. Det nya protokollet har hög effektivitet, vilket gör att små provvolymer kan användas (2 ml jämfört med tidigare flera liter) och därmed ökar hanterbarheten. Vi visar i denna studie att varje steg 7 i DNA-extraktionsprotokollet är viktigt för att ge en hög effektivitet. Detta protokoll kan med fördel användas som vägledning för många olika typer av studier. På grund av att många havsbakterier inte kan bilda kolonier och alltså inte växa på traditionella medier har det varit svårt att få en klar bild av artrikedomen. Molekylärbiologin har dock gjort det möjligt att identifiera bakterier med hjälp av 16S rRNA genen, en enorm mängd gensekvenser från världens alla hav har inkommit till den gemensamma databanken (GenBank). År 2002 gjordes en studie där man sammanställde informationen i denna databank, för att få en bild av artrikedomen i världshaven. Resultatet av denna studie var att det i världshaven fanns färre bakterietyper än vad många forskare har spekulerat i. I denna avhandlig har vi utfört en studie där vi gjorde en stor global provtagning för att se om denna undersökning överensstämde med den datainformativa. Provtagning från nio lokaliteter gjordes i de tempererade, tropiska och polarhaven. Ett genbibliotek från varje lokal gjordes och kloner sekvenserades. Resultatet visar i likhet med den datainformativa undersökningen på en begränsad artrikedom. 80% av gensekvenserna fanns redan i databanken, vilket tyder på att de flesta arter redan har blivit funna. Dessutom visade det sig att få av bakterierna återfanns på alla ställen och många återfanns endast på ett ställe. Utöver detta visade det sig att det fanns en ökad artrikedom ju närmare ekvatorn man kom, vilket tidigare har visats för större organismer. Studierna i denna avhandling har ökat förståelsen för hur sammansättningen av det kvävefixerande bakteriesamhället i Östersjön ser ut samt bidragit till diskussionen om den globala artrikedomen bland bakterioplakton och dess utbredning.
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Crosswhite, F. S., and C. D. Crosswhite. "Nitrogen Fixation in Desert Legumes." University of Arizona (Tucson, AZ), 1988. http://hdl.handle.net/10150/609108.
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Monteiro, Fanny. "Mechanistic models of oceanic nitrogen fixation." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53104.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009.Includes bibliographical references (p. 163-185).
Oceanic nitrogen fixation and biogeochemical interactions between the nitrogen, phosphorus and iron cycles have important implications for the control of primary production and carbon storage in the ocean. The biological process of nitrogen fixation is thought to be particularly important where the ocean is nitrogen limited and oligotrophic. This thesis examines some of the mechanisms responsible for the distribution, rates and temporal variability of nitrogen fixation and its geochemical signature in the modern ocean. I employ simple analytical theories and numerical models of ecosystems and biogeochemical cycles, and closely refer to direct observations of the phytoplanktonic community and geochemical tracers of the marine nitrogen cycle. Time-series observations of geochemical tracers and abundances of nitrogen fixers (or diazotrophs) in the northern subtropical gyres suggest variability in nitrogen fixation on interannual and longer timescales. I use a highly idealized, two-layer model of the nitrogen and phosphorus biogeochemistry and ecology of a subtropical gyre to explore the previously proposed hypothesis that such variability is regulated by an internal biogeochemical oscillator. I find, in certain parameter regimes, self-sustained oscillations in nitrogen fixation, community structure and biogeochemical cycles even with perfectly steady physical forcing. The period of the oscillations is strongly regulated by the exchange rate between the thermocline and mixed-layer waters, suggesting a period of several years to several decades for the North Pacific subtropical gyre regime, but would likely be shorter (only a year or so) for the North Atlantic Ocean.
(cont.) Geochemical tracers such as DINxs (=NO3--16PO3-) measure the oceanic departure from the Redfield ratio. DINx, is often used to estimate the rate of nitrogen fixation in the ocean, by quantifying the tracer accumulation along isopycnals. However this tracer reflects an interwoven set of processes including nitrogen fixation, but also denitrification, atmospheric and riverine sources, differential remineralization and complex transport pathways. I examine analytical solutions of the prognostic equation of DINx, and an idealized three-dimensional model of the basin-scale circulation, biogeochemical cycles and ecology of the North Atlantic Ocean. The two approaches demonstrate that the observations of a subsurface maximum in the North Atlantic Ocean and the temporal variability at the station BATS of DINxs can be explained simply by preferential remineralization of organic phosphorus relative to nitrogen. A further analysis reveals that the current geochemical estimates based on inorganic forms of phosphorus and nitrogen underestimate integrated nitrogen fixation rates by a factor of two to six, by neglecting the preferential remineralization effect. Most current understanding of oceanic nitrogen fixation is based on the Trichodesmium, though unicellular cyanobacteria, diatom-diazotroph associations (DDA) and heterotrophic bacteria might be as important in adding nitrogen into the ocean. I employ a self-assembling global ocean ecosystem model to simulate diverse phytoplanktonic diazotrophs in the global ocean and examine how temperature, oligotrophy, iron and phosphate limitations influence the global marine diazotroph distribution.
(cont.) Analogs of Trichodesmium, unicellular diazotrophs and DDA are successful in the model, showing very similar distributions with observations. The total diazotrophic population is distributed over most of the oligotrophic warm (sub)tropical waters in the model. The model demonstrates that temperature is not the primary control, but suggests instead that diazotroph biogeography is restricted to the low fixed nitrogen oceanic regions which have sufficient dissolved iron and phosphate. The theory of resource competition is used to map out regions of iron and phosphate regulation of diazotroph distribution. The theory suggests that diazotrophs are largely regulated by iron availability, in particular in the Pacific and Indian Oceans. The iron cycle is currently not well enough constrained to confidently predict the diazotroph distribution in global ocean models.
by Fanny Monteiro.
Ph.D.
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Abdel, Magid H. M., P. W. Singleton, and J. W. Tavares. "Sesbania-Rhizobium Specificity and Nitrogen Fixation." University of Arizona (Tucson, AZ), 1988. http://hdl.handle.net/10150/609114.
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The compatibility of potentially nitrogen fixing associations between ten Rhizobium strains and six Sesbania accessions (species) was studied under glasshouse conditions. The rates of N₂ (C₂ H₂) fixation (u moles C₂ H₄ /plant/h) were determined. The various Sesbania accessions responded differently to inoculation with the strains tested. The ANOVA test revealed that there are real accessions (P = 0.01) and strains (P = 0.05) differences. In general the results obtained indicated that the highest mean rate of N₂ (C₂ H₂) fixation and the highest degree of compatibility with strains under test was shown by Sesbania bispinosa (accession BA12). Sesbania grandiflora (accession GL 2.02) ranked next. The performance of Sesbania pachycarpa (accession PCI), Sesbania macrantha (accession MNI), and Sesbania sesban (accession SBIO) in the N₂ (C₂ H₂) assay is lower than that of accessions BAI2 and GL2.02, thus indicating the possibility of lack of compatibility between these three accessions and almost all of the Rhizobium strains studied. Plants of Sesbania rostrata (accession RSI) produced either extremely low or no ethylene (C₂ H₄) quantities in the N₂ (C₂ H₂) assay thus indicative of high specificity or that this legume is not promiscuous at all. However, inoculated and fertilized Sesbania rostrata performed quite satisfactorily and formed profuse N₂-fixing nodules on roots and stems when grown in potted soil under Central Saudi Arabia climatic conditions. The results obtained indicated high variability among treatments in nodule number.
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Nagel, Eric Dale. "Nitrogen fixation in benthic microalgal mats." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2092.
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Thesis (M.S.) -- University of Maryland, College Park, 2004.Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Buchwald, Carolyn. "Nitrogen cycling in oxygen deficient zones : insights from [delta]¹⁵N and [delta]¹⁸O of nitrite and nitrate." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79346.
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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.In title on title page, "[delta]" appears as lower case Greek letters. Cataloged from PDF version of thesis.
Includes bibliographical references.
The stable isotopes, [delta]¹⁵N and [delta]¹⁸O, of nitrite and nitrate can be powerful tools used to interpret nitrogen cycling in the ocean. They are particularly useful in regions of the ocean where there are multiple sources and sinks of nitrogenous nutrients, which concentration profiles alone cannot distinguish. Examples of such regions are "oxygen deficient zones" (ODZ). They are of particular interest because they are also important hot spots of fixed N loss and production of N₂O, a potent greenhouse gas. In order to interpret these isotope profiles, the isotope systematics of each process involved must be known so that we can distinguish the isotopic signature of each process. One of the important processes to consider here is nitrification, the process by which ammonium is oxidized nitrite and then to nitrate. This thesis describes numerous experiments using both cultures of nitrifying organisms as well as natural seawater samples to determine the oxygen isotope systematics of nitrification. These experimental incubations show that the accumulation of nitrite has a large effect on the resulting [delta]¹⁸ONO3. In experiments where nitrite does not accumulate, [delta]¹⁸ONO3 produced from nitrification is between -1 to l%o. These values will be applicable for the majority of the ocean, but the nitrite isotopic exchange will be important in the regions of the ocean where nitrite accumulates, such as the base of the euphotic zone and oxygen deficient zones. [delta]¹⁸ONO2 was developed as a unique tracer in this thesis because it undergoes abiotic equilibration with water [delta]¹⁸O at a predictable rate based on pH, temperature and salinity. This rate, its dependencies, and how the [delta]¹⁸ONO2 values can be used as not only biological source indicators but also indicators of age are described. This method was applied to samples from the primary nitrite maximum in the Arabian Sea, revealing that the dominant source and sinks of nitrite are ammonia oxidation and nitrite oxidation with an average age of 37 days. Finally, using the isotope systematics of nitrification as well as the properties of nitrite oxygen isotope exchange described in this thesis, the final chapter interprets multiisotope nitrate and nitrite profiles in the Costa Rica Upwelling Dome using a simple ID model. The nitrite isotopes showed that there were multiple sources of nitrite in the primary nitrite maximum including (1) decoupling of ammonia oxidation and nitrite oxidation, (2) nitrate reduction during assimilation and leakage of nitrite by phytoplankton. In the oxygen deficient zone and secondary nitrite maximum, there were equal contributions of nitrite removal from nitrite oxidation and nitrite reduction. This recycling of nitrite to nitrate through oxidation indicates that the percentage of reduced nitrate fully consumed to N2 gas is actually smaller than previous estimates. Overall, this thesis describes new nitrogen and oxygen isotopic tracers and uses them to elucidate the complicated nitrogen biogeochemistry in oxygen deficient zones.
by Carolyn Buchwald.
Ph.D.
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Al-Taani, Ahmed A. "Non-biological fixation of atmospheric nitrogen to nitrate on titanium dioxide and desert soil surfaces." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3339090.
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Heidari, Sharif Abad Hossein. "Variation in the sensitivity of nodulation and nitrogen fixation to nitrate in annual "Medicago" species." Title page, table of contents and abstract only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phh465.pdf.
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Bibliography: leaves 153-179. Annual species of Medicago, or medics, are important pasture legumes in the neutral to alkaline soils of southern Australia but their nodulation and nitrogen fixation processes are retarded by soil nitrate. This study ascertains whether an observed tolerance to nitrate among medic species can be substantiated, and attempts to understand the underlying factors responsible.
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Keuter, Andreas. "Nitrogen response efficiency, nitrogen retention efficiency, and asymbiotic biological nitrogen fixation of a temperate permanent grassland site under different sward compositions and management practices." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://hdl.handle.net/11858/00-1735-0000-000D-FCBE-5.
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Cai, Jingya. "Phenotypic Analysis of Medicago truncatula NPF1.7 Over-Expressing Plants Grown under Different Nitrate Conditions." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062858/.
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Plants have many nitrate transporters; in the model legume Medicago truncatula, MtNPF1.7 is among them. MtNPF1.7 is important for M. truncatula growth and it has been established that MtNPF1.7 is a high affinity nitrate transporter. M. truncatula plants with mutations in MtNPF1.7 gene show defects during plants growth, with striking abnormalities in nodule development and root architecture. Nitrogen fixation is an energy expensive process; when legumes have sufficient bioavailable nitrogen like nitrate available, it suppresses nodulation and nitrogen fixation. Previous preliminary results in our lab showed that plants constitutively expressing MtNPF1.7 have a growth phenotype in the absence of nitrate, but no data was available on how M. truncatula plants constitutively expressing MtNPF1.7 are affected by the presence of nitrate. For my research, I confirmed the preliminary results on the growth of M. truncatula plants overexpressing NPF1.7 and examined these plants' phenotypes when nitrate was not provided in the growth media and when it was provided at two different concentrations. Compared with wild type A17, plants constitutively expressing MtNPF1.7 gene grow larger, have more lateral roots and more nodules when grown in the absence of nitrate and when 0.2 mM KNO3 was provided. At 1 mM KNO3, there are fewer differences between wild type A17 and plants constitutively expressing the MtNPF1.7 gene. Compared with wild type A17, plants constitutively expressing the MtNPF1.7 gene flower earlier, which indicates MtNPF1.7 gene may have a function in plant flowering.
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Kahindi, James H. P. "Efficiency of nitrogen fixation in Azotobacter chroococcum." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358929.
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Allan, Caroline Elizabeth. "Nitrogen fixation in riverine wetland plant communities." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297033.
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Pakseresht, Nima. "An in silico investigation into nitrogen fixation." Thesis, University of East Anglia, 2010. https://ueaeprints.uea.ac.uk/19406/.
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Sanyal, Debankur. "Symbiotic Nitrogen Fixation in Dry Bean Cultivars." Diss., North Dakota State University, 2018. https://hdl.handle.net/10365/27850.
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Dry Beans (Phaseolus vulgaris L.), is the second-most important grain legume, and North Dakota has ranked first in dry bean production. The overarching research question of my project is whether we can increase the nitrogen (N) fixing potential of dry bean cultivars with inoculation and compare the nitrogen (N) fixing potential of common dry bean cultivars. Field experiment was conducted to compare peat and liquid inoculants during 2016 and 2017 growing seasons. In the field study, N2 fixation was estimated by stable isotope (15N) dilution technique. Liquid inoculant (70.5?5.9 kg ha-1) showed similar potential to the peat based inoculant (60.5?4.7 kg ha-1) for N2 fixation, however, inoculation treatments did not increase the N2 fixation over uninoculated (control). Further, it was investigated the nifH gene (marker for N2 fixation) expression in the dry bean-Rhizobium phaseoli symbiotic system. It was found that the relative normalized nifH gene expression significantly correlates (r = 0.82) with the total amount of N2 fixed, indicating the genetic control of symbiotic efficiency. Study on N-assimilatory genes, NR for nitrate reductase and GS for glutamine synthetase, showed that N2 fixation alone could not support plant N need in the later stages of growth (i.e. late flowering) and supplementary application of mineral-N is necessary for better plant growth and economic-yield. Dry bean cultivars did not response to inoculation and genetically, they differed significantly in N2 fixation potentials.Specialty Crop Block Grant
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Karriem, Fatiema. "Oxidative fixation of dinitrogen by photocatalysis." Thesis, University of Western Cape, 2000. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5777_1267648612.
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The heterogeneous photocatalytic oxidation of dinitrogen to nitrate, NO3 and/or nitrite, no2 using peroxy species of titanium (IV) in aqueous suspensions has been investigated. The photocatalysts used were titanium peroxide and Degussa p25 TiO2 pretreated with H2O2. These photocatalysts were investigated by SEM and FTIR spectroscopy.
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Cheng, J. "Interactions between nitrogen fixation and alternative sources of nitrogen in Gloeothece." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636244.
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When grown under constant illumination, Gloeothece ATCC 27152, a unicellular cyanobacterium, can use nitrate, nitrite, dinitrogen or ammonium as the sole N-source for growth. The uptake systems for nitrate and nitrite were fully active and ammonium-repressible in N2-fixing cultures. Nitrite uptake was mediated via two pH-dependent systems: passive diffusion of HNO2 and active transport of nitrite. Nitrate uptake was highly light-dependent. Ammonium was also transported by passive diffusion of ammonia and active uptake of ammonium, depending on the pH of the medium. Ammonium inhibited nitrate uptake almost completely, but inhibited nitrite uptake only partially. The true inhibitor was a product of ammonium assimilation, possibly glutamine, rather than ammonium itself, since L-methionine-DL-sulphoximine, an inhibitor of glutamine synthetase blocked GS activity very quickly and decreased the inhibitory effect of ammonium. On the other hand, the inhibitory effect of nitrite on ammonium uptake was stronger than that of nitrate. Nitrate and nitrite competitively inhibited each other's assimilation, occurring at the uptake stage. This suggested that nitrate and nitrite were transported by a common transporter in Gloeothece. The rates of nitrate and nitrite uptake were similar, but the uptake of ammonium was much faster than that of either nitrate of nitrite. In contrast to the uptake systems, systems of nitrate and nitrite reductions were substrate-inducible. Ammonium, either generated intracellularly or supplied exogenously, was assimilated via the GS-GOGAT pathway. Nitrite and ammonium inhibited N2 fixation rapidly. Nitrate inhibited N2 fixation less rapidly and less extensively, and often temporarily stimulated nitrogenase activity. The inhibitory effects of nitrate and ammonium could be prevented by L-methionine-DL-sulphoximine, suggesting that the true inhibitor of N2 fixation was an assimilatory product of ammonium rather than ammonium or nitrate itself.
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Mansur, Irdika. "Nitrogen uptake dynamics and biological nitrogen fixation in a silvopastoral system." Thesis, University of Canterbury. Department of Forestry, 1994. http://hdl.handle.net/10092/4243.
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Two sets of field experiment were conducted at the Lincoln University's agroforestry trial. The first experiment was to study nitrogen (N) uptake by radiata pine and pasture, and soil total N changes with time. The second experiment was to assess the magnitude of input from biological nitrogen fixation (BNF) and factors affecting BNF. Lucerne was found to be the most severe competitor with trees. It reduced tree height, root collar diameter and diameter at breast height, and occasionally reduced fascicle dry weight and foliar N content. However, lucerne had a high dry matter yield (DMY), nitrogen concentrations, nitrogen yields, and amounts of nitrogen fixed. It had lower percentage of N derived from atmosphere (%Ndfa) than clover which resulted in a high N removal from the lucerne plot, when the herbage was removed as silage. Clover has high %Ndfa during spring and summer ranging from 83 to 97%. Radiata pine did not affect total N concentration of pastures and %Ndfa of the legumes. However, radiata pine reduced seasonal DMY of the pastures and seasonal and annual DMY of legumes, which led to the reduction of N yield and amount of N fixed. Clovers in ryegrass/clover, cocksfoot/clover and phalaris/clover were estimated to fix 134,71, and 75 kg N ha ⁻¹ year ⁻¹ which were lower than lucerne which was estimated to fix 230 kg N ha ⁻¹ year ⁻¹. The variations of amounts of N fixed by clover in different grass/clover mixtures were due to the persistence and productivity of the clover in pasture mixtures. Nitrogen balance in all pasture treatments was negative showing that N removal in herbage exceeded N input from BNF. Similarly, the total N in the soil decreased with time. Biological nitrogen fixation was important to stabilise N balance in pasture by minimising soil N removal and to ensure a high pasture productivity. Soil moisture and N were likely to be the important resources competed for by pasture plants and the trees. However, the effect of competition was more apparent on altering N status of the trees than that of the pastures. The N status of radiata pine grown with pastures was occasionally marginal. Soil moisture content close to the row of trees was lower than that at the midway between two rows of trees. Rain shadow effect from trees further lowered the moisture content of soil to the north side of trees. Overall the use of ¹⁵N isotope dilution technique for measuring %Ndfa and percentage of grass N derived from transfer (%Ndftrans) has given satisfactory results. Nitrogen transfer from clover to ryegrass/clover was considered as insignificant (<1.5 g m ⁻² annually). The atom % ¹⁵N enrichment in the soil decreased with time.
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Rosalino, Pedro Krauspenhar. "MANEJO DO SOLO NA ENTRESSAFRA DO ARROZ E SUA INFLUÊNCIA NA EMISSÃO DE GASES DE EFEITO ESTUFA E NA PRODUTIVIDADE DA CULTURA DA SOJA." Universidade Federal de Santa Maria, 2014. http://repositorio.ufsm.br/handle/1/4887.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe soybean (Glycine max) cultivation in rotation with rice (Oryza sativa) in paddy soils is a growing practice in the state of Rio Grande do Sul. However, there is little information on the emission of methane (CH4) and nitrous oxide (N2O) during soybean growing season in lowland and the contribution of biological nitrogen fixation (BNF) for crops in this environment. The study was aimed to evaluate the emissions of CH4 and N2O, BNF and soybean productivity in lowland managed for three years with different systems of soil tillage/straw after the rice harvest. The experiment was conducted during the growing season of 2012/2013 on a Plano soil. The treatments consisted of different systems of soil management/straw applied for three years after the rice harvest: ryegrass (RY), disc harrow (DH), knife-roller (KR), fallow + disc harrow (F + DH), disc harrow + disc harrow (DH + DH), knife-roller + disc harrow (KR + DH), removal of straw (RS) and fallow (F). Besides these, a natural lowland (NL) was used as control. The NL had the lowest N2O emissions; however CH4-C (161 kg ha-1) emissions were higher when compared to soybean cultivated in lowland. The highest N2O emissions occurred from soybean cultivation, being observed in the treatment RY where the highest cumulative emission was 7.9 kg N2O-N ha-1. The management of soil/straw performed with DH, compared to systems with KR and F, caused increased density by up to 10% and reduction in macro-porosity and total porosity in the topsoil. Changes in soil physical properties caused by different soil/straw tillage systems did not result in a decreased N accumulation, BNF contribution (mean 67%) and productivity of soybean.
O cultivo da soja (Glycine Max) em rotação com o arroz (Oryza sativa) em solos de várzea é uma prática crescente no estado do Rio Grande do Sul (RS). No entanto, existem poucas informações sobre a emissão de metano (CH4) e óxido nitroso (N2O) durante o cultivo da soja em várzea e a contribuição da fixação biológica (FBN) para a cultura nesse ambiente. O estudo teve por objetivo avaliar as emissões de CH4 e N2O, a FBN e a produtividade da soja em várzea manejada durante três anos com diferentes sistemas de manejo do solo/palha após a colheita do arroz. O experimento foi conduzido no ano agrícola 2012/2013 em um Planossolo Hidromórfico Eutrófico arênico. Os tratamentos foram compostos por diferentes sistemas de manejo do solo/palha aplicados durante três anos após a colheita do arroz: azevém (AZ), grade (G), rolo-faca (RF), pousio + grade (P+G), grade + grade (G+G), rolo-faca + grade (RF+G), retirada da palha (RP) e pousio (P). Além desses, foi avaliada uma área natural de banhado (AN) que serviu como testemunha. A AN apresentou as menores emissões de N2O, porém elevada emissão de C-CH4 (161 kg ha-1) quando comparada ao cultivo da soja em várzea. As maiores emissões de N2O ocorreram no período de cultivo da soja, sendo observada no tratamento AZ a maior emissão acumulada desse gás (7,9 kg de N-N2O ha-1). O manejo do solo/palha realizado com G, comparado aos sistemas com RF e P, provocam aumento da densidade em até 10% e redução na macroporosidade e porosidade total na camada superficial do solo. As modificações causadas nos atributos físicos do solo pelos diferentes sistemas de manejo do solo/palha, não resultaram em diminuição no acúmulo de N, contribuição da FBN (média de 67%) e produtividade de grãos de soja.
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Denton, Matt. "Influence of naturalised Rhizobium leguminosarum bv. trifolii populations on the nodulation of alternative clovers (Trifolium spp.) in alkaline soils / Matt Denton." Adelaide, Sth. Aust, 2000. http://hdl.handle.net/2440/22423.
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Bibliography: leaves 186-209.xiii, 218 leaves : ill. (some col.), 1 col. map ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--Adelaide University, Dept. of Agronomy and Farming Systems, 2000
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Denton, Matt. "The influence of naturalised Rhizobium leguminosarum bv. trifolii populations on the nodulation of alternative clovers (Trifolium spp.) in alkaline soils / Matt Denton." Thesis, Adelaide, Sth. Aust, 2000. http://hdl.handle.net/2440/22423.
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Lestari, Yulin. "Nodulation and nitrogen fixation in Medicago species at low pH." Title page, contents and summary only, 1993. http://web4.library.adelaide.edu.au/theses/09PH/09phl6418.pdf.
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Zhou, Maoqian 1961. "Nitrogen fixation by alfalfa as affected by salt stress and nitrogen levels." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277231.
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The growth and Nitrogen fixation by one low salt tolerant alfalfa (Medicago sativa L.) and two germination salt tolerant selections inoculated with were investigated at two salt levels (0, -0.6 Mpa) and two N rates (1, 5ppm) using a system which automatically recirculates a nutrient solution. The high level of salinity (-0.6 Mpa osmotic potential of culture solution) resulted in substantial reduction in the N fixation percentage and total fixed N. The effect of salinity was more pronounced for later cuttings than for the earlier cutting. The N fixation percentages were substantially decreased by increasing N level and the reduction was enhanced by time. The N treatment levels did not exhibit a significant effect on total fixed N. Cultivars did not differ in either growth or N fixation. However, the interaction of N and salinity significantly decreased the percentage and amount of N fixation.
29
Bradburn, Mark James. "Light and planktonic nitrogen fixation in Colorado reservoirs." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1442959.
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Ghalamboran, M. R. "Symbiotic nitrogen fixation enhancement due to magnetite nanoparticles." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/8172.
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Population pressure on food production motivates the search for new ways to increase the productivity of arable land, especially land rendered marginal by salinity or aridity. The global thesis motivating this work is that nanotechnology can benefit agriculture. My specific thesis is that that part of nanotechnology concerned with nanoparticle production can benefit soybean yield. I have focused on symbiotic nitrogen fixation, and systematically investigated the effects thereon of magnetite nanoparticles introduced into the rhizosphere. My main finding is that the presence of these nanoparticles increases nodulation - both the number of nodules and the size of individual nodules. Since the experiments were carried out on plants provided with minimal nutrients, there was no corresponding increase in vegetative growth. Some evidence was obtained for the nanoparticles enhancing the "molecular dialogue" between soybean root and the Bradyrhizobia that become incorporated in the nodules. A secondary finding is that the nanoparticles enhance the growth rate of Bradyrhizobia in culture, which is advantageous for the preparation of inocula. Furthermore, coating soybean seeds with nanoparticles and Bradyrhizobia prior to planting enhances survival of the bacteria, and therefore increases the efficiency of subsequent nodulation.
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Chan, Y. S. Gilbert. "Nitrogen fixation by leguminous plants under landfill conditions." Thesis, Durham University, 1994. http://etheses.dur.ac.uk/1702/.
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Wang, He. "Metabolic regulation of nitrogen fixation in Rhodospirillum rubrum /." Stockholm : Department of biochemistry and biophysics, Stockholm university, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-29404.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2009.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Submitted. Härtill 4 uppsatser.
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Amiri, Alireza Agha. "Regulation of nitrogen fixation in rhizobia-legume symbioses." Thesis, Amiri, Alireza Agha (2021) Regulation of nitrogen fixation in rhizobia-legume symbioses. Honours thesis, Murdoch University, 2021. https://researchrepository.murdoch.edu.au/id/eprint/63559/.
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Rhizobia are soil-dwelling bacteria capable of infecting legume roots and forming a symbiotic association. Inside root nodules, low O2 levels trigger expression of the nitrogenase enzyme complex in rhizobia, allowing them to fix atmospheric N2 into NH3, and secrete this reduced nitrogen source to the host plant. Rhizobial N2 fixation is activated via the transcriptional regulator NifA, which is itself induced by low O2 concentration in legume root nodules, most commonly via the two-component sensor-regulator FixLJ or a modified version of this regulon. For rhizobia in the genus Mesorhizobium, it is currently unclear how low O2 tension is sensed and transduced into a signal to activate N2 fixation, with the FixLJ system shown to be dispensable for N2 fixation. Mesorhizobium ciceri CC1192, which forms a symbiosis with Cicer arietinum (chickpea) and is the commercial inoculant for this crop legume in Australia, harbours fixV, a putative LacI/GalR transcriptional regulator which may directly control the expression of nifA in this strain. To investigate the role of fixV and nifA within CC1192, inactivation vectors were constructed in the suicide vector pJQ200SK via Gibson Assembly and fixV and nifA deletion mutants generated, along with a nitrogenase null mutant (nifH) as a non-N2-fixing control. nifH mutants were symbiotically defective on C. arietinum, with nitrogenase activity completely abolished. Deletion of fixV resulted in reduced, but not abolished, nitrogenase activity on a per nodule basis and reduced foliage dry weights, while the ΔnifA mutant phenotype remains to be tested. FixV, therefore, is not essential for N2 fixation in CC1192 but likely plays a vital role alongside another as yet unidentified regulator.
34
Kessler, Peter S. "Nitrogen fixation in the mesophilic marine archaeon Methanococcus maripaludis /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11520.
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Abi-Ghanem, Rita. "Optimizing biological nitrogen fixation and evaluating Iraqi extension education." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Summer2009/R_Abi-Ghanem_070909.pdf.
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Horak, Rachel Elizabeth Ann. "Controls on nitrogen fixation and nitrogen release in a diazotrophic endosymbiont of shipworms." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37238.
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Nitrogen fixation is an ecologically important microbial process that can contribute bioavailable combined N to habitats low in N. Shipworms, or wood-boring bivalves, host N2-fixing and cellulolytic symbiotic bacteria in gill bacteriocytes, which have been implicated as a necessary adaptation to an N-poor C-rich (wooden) diet. Shipworm symbionts are known to fix N within the gill habitat and newly fixed N is subsequently incorporated into non-symbiont containing host tissue. The presence of N2-fixation in gill bacteriocytes presents a conundrum because N2-fixation is tightly regulated by oxygen in most other diazotrophic microbes. Also, the direct evidence of new N being incorporated into the host tissue indicates that there are potentially complex nutrient cycles in this symbiosis, which have not been investigated. We used the cultivated symbiont Teredinibacter turnerae, which has been isolated from many shipworm species, as a model organism to elucidate controls on N2-fixation and N release in the shipworm symbiosis. Our results indicate that headspace oxygen concentration does not control biomass specific N2-fixation and respiration activity in T. turnerae, but it does influence the magnitude of the growth rate and timing of culture growth. Also, we examined the controls of oxygen on inorganic nutrient uptake rates, and documented a small amount of dissolved inorganic nitrogen release. While the N budget is only partially balanced, we provide indirect evidence for the allocation of fixed N to the excretion of exopolymeric substances and dissolved organic nitrogen; future studies that measure these additional N sinks are necessary to close the N budget. Although there are limitations of using pure cultures to investigate a complex symbiotic system, this study provides direct experimental evidence that T. turnerae has adaptations that are conducive to N2-fixation in gill bacteriocytes.
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MOHAMED, IBRAHIM ELBASHIR. "EFFECTS OF PRE-PLANT APPLICATION OF NITROGEN FERTILIZER ON SYMBIOTIC NITROGEN FIXATION AND YIELD OF COWPEAS (VIGNA UNGUICULATA (L.) WALP.)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187957.
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The responses of two cowpea (Vigna unguiculata (L.) Walp.) cultivars inoculated with granular inoculum (a mixture of rhizobia) at different levels of applied nitrogen were evaluated. California Blackeye 5 (Ca5) and Knuckle Purple Hull (KPH) cowpeas were examined under field conditions for percent nodulation, nodule number, and nodule mass per plant, and nitrogenase activity at various times during the 1983 and 1984 growing seasons. Data were also obtained for shoot and root dry weights, seed yield, and protein content. Significant differences between inoculated and uninoculated plots were found at all nitrogen treatments for both cultivars with respect to nodulation percentage, nodule number, nodule mass, and nitrogenase activity. An inverse trend linear and quadratic was noted between nitrogen increments and nodulation (nodule number and nodule mass) of Ca5 and KPH cowpeas. High N (168 kg N ha('-1)) was more inhibitory to nodulation than low (28 kg N ha('-1)) N applied. Nitrogenase activity of both cultivars was significantly stimulated with low and inhibited by high levels of ammonium nitrate. Effects of nitrogen treatments on nodulation and nitrogenase activity were influenced by the stage of growth and cowpea cultivar. At the pod-fill stage, higher nodule numbers and nitrogenase activity were recorded for Ca5 as compared to KPH cowpeas. Morphological differences, with Ca5 plants being erect with few vines, whereas KPH plants were semi-erect and bushy, were observed between inoculated and uninoculated plants of Ca5 and KPH cowpeas at all levels of applied nitrogen. Dry weights of vegetative components of both cultivars were significantly improved when low (28 kg N ha('-1)) rather than high (168 kg N ha('-1)) nitrogen was added. Inoculation significantly increased seed yield of Ca5 cowpeas. When conditions were favorable seed yield of inoculated Ca5 exceeded that of inoculated KPH in all comparisons within the same increments of applied N. Seed yield of both cultivars was adversely affected when high levels of nitrogen were applied. Seed, leaf, petiole, and stem protein content were significantly higher with respect to inoculated than uninoculated plots. However, nitrogen fertilizers tended to decrease protein content of the measured parameters for Ca5 and KPH cowpeas.
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Park, Rosa. "Investigating new reactions for coordinated dinitrogen." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2344.
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The chemistry of the tantalum dinitrogen complex ([NPN]Ta)₂(μ-H)₂(μ-η¹:η²-N₂)Ta-[NPN], 1, (where [NPN] represents the acyclic tridentate ligand [(PhNSiMe₂CH₂)₂-PPh]²-), with primary alkenes, group IV and V metallocene complexes, and GaCp* is explored.
The reaction of 1 with 1-pentene and 1-hexene occurs via olefin-insertion into the metal-hydride bond to give two new complexes, ([NPN]Ta(CH₂)₄CH₃)₂(μ-η¹:η¹-N₂), 10, and ([NPN]Ta(CH₂)₅CH₃)₂(μ-η¹:η¹-N₂), 11, which were characterized using NMR spectroscopy. The solid-state structure of 11 was established and revealed that N₂ has been transformed into a bridging end-on mode. In contrast to its G symmetry in solution, the solid-state structure of 11 is C, symmetric; a VT-NMR study was performed and showed that 11 exists as an equilibrium between two isomers in solution: a C, symmetric isomer 11A,which is the predominant isomer at room temperature, and a C, symmetric isomer 11B,which is the minor isomer.
The reactivity of 1 with group IV and V metallocenes was investigated. The reaction of 1 with Cp₂Hf(PMe₃)(η²-Me₃SiCCSiMe₃) produces [N(μ-P=N)N]Ta(μ-H)₂(μ-N(Hf-Cp₂))Ta[NPN], 14, in which N₂ is cleaved and new Hf-N and P=N bonds have formed. The reaction of 1 with group V metallocene hydrides Cp₂MH₃ (M Nb, Ta) was also attempted however these complexes do not react with 1.
The reaction of 1 with GaCp* produces a new complex, [NPN]Ta(μ-N(GaCp*))Ta(=NPμ)[NPIA,-N], 18, which was characterized using NMR spectroscopy. Complex 18 decomposes over several days in solution, and one product of decomposition that was isolated was [(PhNH)(NPμ-N)Ta]₂, 19. The solid-state structure of 19 showed that the [NPN] ligand was cleaved at the N-Si bond, similar to that observed for the reaction of 1 with 9-BBN and HB(C₆H₅)₂. A mechanism for the formation of complexes 18 and 19 is proposed.
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Beeson, Keri Elizabeth. "Differentiation of plasmids in marine diazotroph assemblages determined by randomly amplified polymorphic DNA analysis." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/25366.
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Harris, Sharman Donna. "Synthesis and investigation of some new complexes of molybdenum (II) and tungsten (II) containing sulphur donor ligands." Thesis, Bangor University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262486.
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Jones, Clare. "Expression of FixAB : a putative member of the electron transfer flavoprotein superfamily." Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365028.
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Jepson, Brian John Nicholas. "Characterisation of anfa, the transcriptional activator of the FE-nitrogenase from Aztobacter vinelandii." Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251439.
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Cheng, Qi. "Studies in the expression and function of Klebsiella pneumoniae nitrogenase iron protein in the chloroplast of the eukaryotic unicellular green algae - Chlamydomonas reinhardtii." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302041.
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Brewin, Brett. "Mechanism of ammonium excretion in NifL mutants of Azotobacter vinelandii." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323244.
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Alias, Yatimah. "Molybdenum-nitrogen chemistry : electrochemical ligand cleavage and coupling reactions; routes to chiral complexes." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267707.
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Naab, JB, SMB Chimphango, and FD Dakora. "N2 fixation in cowpea plants grown in farmers' fields in the Upper West Region of Ghana, measured using 15N natural abundance." Symbiosis, 2009. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001478.
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Abstract
Few studies have assessed the levels of symbiotic N nutrition in legumes grown by fanners in Africa. In this study, the
shoots of cowpea plants were sampled from 63 farms in 12 villages within 5 districts of the Upper West Region of Ghana,
and assessed for growth and symbiotic N nutrition. The data revealed considerable differences in cowpea plant density per
m2
, plant growth, 15N natural abundance (OI5N), %Ndfa, and N-fixed among different farms under one village, and between
villages under the same district, and between districts in the Upper West Region. In farms where there were fewer cowpea
plants per m2
, plant growth was better and dry matter yield per plant significantly greater, leading to strong variations in
O!5N values. Except for four farms at Bamahu which had cowpea shoot Ndfa values of 12.1%,30.0%,36.5% and 46.6%,
one farm at Babile with Ndfa value of 58.1%, and three farms at Silbelle with Ndfa values of56.8%, 57.9% and 68.7%, the
remaining 55 out of the 63 farms studied showed high shoot Ndfa values, ranging from 70.6% to 99.7%, which clearly
indicates that cowpea cultivated by farmers in the Upper West Region of Ghana meet a large proportion of their N
requirements from symbiotic fixation. At the district level, isotopic analysis showed that, on average, the 15N natural
abundance values (%0) of cowpea shoots were -0.496±0.04 for Jirapa, -O.083±0.06 for Nadowli, 0.368±O.08 for Lawra,
l.333±0.29 for Wa and 0.365±0.09 for Sissala district. Estimates of the legume's N derived from fixation were 66.3% for
Wa district, 89.9% for Nadowli, 79.4% for Lawra, 78.9% for Sissala and 80.9% for Jirapa district. The amount ofN-fixed
ranged from 402.3 mg.plant' for Nadowli, 176.5 mg.plant" for Wa, 235.4 mg.plant' for Sissala, 179.0 rng.plant' for
Lawra to 249.2 mg.plane! for the Jirapa district. Expressed on per-hectare basis using cowpea density per m2
, the total
amount ofN-fixed was around 16.6 kg ha-! in the Nadowli district, 19.1 kg ha-! in Wa, 23.0 kg ha' in Sissala, 21.1 kg ha-I
in Lawra and 17.6 kg ha-1in the Jirapa district. Averaged across all 5 districts, N-fixed by cowpea was about 19.5 kg ha-! in
the Upper West Region of Ghana. These data suggest that, increasing N2 fixation in fanners' fields in Ghana would require
optimization of cowpea plant density rather than biological manipulation of the symbiotic process (as %Ndfa values were
generally very high).
47
Edwards, Robert A. "The role of uridylytransferase in the regulation of nitrogen control in Klebsiella pneumoniae." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239114.
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Brunner, Samantha Marie. "Impact of Nitrogen and Rhizobial Seed Inoculants on Soybean Aphid (Aphis Glycines Matsumura) Densities." Thesis, North Dakota State University, 2012. https://hdl.handle.net/10365/26560.
Full textAbstract:
Soybeans are able to obtain nitrogen from two different sources, nitrogen found in the soil (e.g. from fertilizers) and biologically fixed nitrogen (from symbiotic bacteria called rhizobia). Nitrogen source and degree of reliance on N-fixation can impact plant nitrogen dynamics, which has the potential to impact above-ground herbivore performance. We examined the impact of nitrogen availability and rhizobial association on soybean aphid biology and reproduction in a series of greenhouse and field experiments. Aphid establishment on plants was not significantly affected in any experiment. However, aphid reproduction was significantly affected by rate of nitrogen fertilization, rhizobial inoculation, and type of rhizobial seed inoculant. In general, aphid densities were not correlated with plant parameters associated with plant nitrogen or N-fixation. Producers commonly use fertilizers and rhizobial seed inoculants, thus it is important to continue exploring the mechanisms underlying how plant nitrogen dynamics impact soybean insect pests.
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Salo, Lucinda Faith. "COMPETITION BETWEEN STRAINS OF RHIZOBIA FOR NODULATION OF LEUCAENA LEUCOCEPHALA (LEGUME)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275326.
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Gier, Jessica [Verfasser]. "Benthic nitrogen fixation in oxygen minimum zones / Jessica Gier." Kiel : Universitätsbibliothek Kiel, 2016. http://d-nb.info/1098185048/34.
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