Nitrification is central to the global cycling of nitrogen and is important for primary production and other processes in marine systems, where nitrogen is generally the limiting nutrient. The majority of studies on nitrification, however, have focused on terrestrial systems, where this process can cause significant losses of N-based fertilisers from agricultural land. Comparatively little is known of nitrification in marine systems and the organisms involved. In addition, technical difficulties in isolation of pure cultures of ammonia-oxidising bacteria have severely restricted studies of species diversity and community structure of these organisms. In this study, molecular technology, based on the 16S ribosomal RNA (rRNA) molecule was applied to the characterisation of marine communities of ammonia-oxidising bacteria. PCR primers were designed for specific amplification of the rRNA gene (rDNA) from ammonia-oxidisers belonging to the beta-subdivision of the Proteobacteria. These primers were used to characterise both enrichment cultures and communities within polluted and unpolluted sediment samples. These studies indicated considerable diversity of beta-subgroup ammonia-oxidisers within marine systems which has not previously been detected. It was also shown that enrichment and isolation techniques select for strains belonging to the genus Nitrosomonas while the majority of sequences obtained by direct analysis of rDNA amplified from total genomic extracts belonged to the genus Nitrosospira. In addition, novel isolation methods were developed which considerably reduced the level of heterotrophic contamination and greatly facilitated isolation of pure cultures. In situ probing, using fluorescently labelled rRNA oligonucleotide probes, indicated that CCD microscopy is less sensitive than UV microscopy alone due to quenching of the signal.

The response of frog sciatic nerve action potentials to x-irradiation and metabolic (carbon monoxide) or transport (ouabain) inhibition was determined in an attempt to further identify the nature of radiation insult to nervous tissue. Carbon monoxide, ouabain (2 X 10-5 M), and nitrogen anoxia were shown to produce a near linear decline in action potential amplitude. The carbon monoxide and nitrogen inhibitions of activity were reversible in air; the carbon monoxide inhibition was light reversible. Ouabain inhibition was partially reversible by soaking the nerve in aerated Ringer's. Application of 120 kv x-rays (75 Kr at 4.9 Kr/min) to nerves during the linear decline in spike amplitude brought about a marked enhancement (146%) of inhibition by 99% CO/l% 02, nitrogen (136%), and ouabain (265%). All bhanges were shown to be statistically significant by a regression analysis. However, x-irradiation did not appear to alter the air reversibility of carbon monoxide and nitrogen inhibitions nor the reversibility in Ringerts of the ouabain inhibition. Additionally x-irradiation completely blocked light reversal of 98% CO/2% 02 inhibition and produced a decline in activity. A possible interpretation of these results is a compensation for radiation action at this dosage requiring metabolism and ion pump activity.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) which is released naturally into the atmosphere as a by-product of the microbial processes of nitrification and denitrification. Agricultural activities are believed to account for up to 80% of anthropogenic N2O emissions at a global scale; however, these estimates are prone to large uncertainties due to the large temporal and spatial variability associated with flux measurements. This thesis contains five studies which aimed to improve the ability to measure and predict N2O emissions from agricultural activities. A closed loop dynamic chamber was developed using a quantum cascade laser (QCL). This method provided high precision chamber measurements of N2O flux from soils with a detection limit below 4 μg N2O-N m-2 h-1. Using the dynamic chamber method allowed for a detailed investigation of uncertainties in individual measurements including contributions from regression fitting, temperature and pressure. The lack of negative fluxes measured that were outwith the detection limits of the methodology (0.3% of all measurements) highlighted that the uptake of N2O reported in some previous literature is likely to have been the result of detection limits of measurement methods applied. Spatial variability of N2O flux was investigated at the plot, field and farm scale. Fluxes were measured from a grassland field plot before and after a tillage event. These measurements highlighted the large spatially variability present in N2O fluxes from agricultural soils. Fluxes varied by up to three orders of magnitude over distances less than 5 metres after the tillage event. A field scale experiment carried out on grazed grassland investigated relationships between soil properties and N2O flux. This study found that N2O emissions correlated strongly with available nitrogen content in the soil and that animal waste was likely responsible for the spatial variability of N2O flux observed at the field scale. A farm scale inventory of N2O emissions was carried out investigating several large point sources of N2O and emissions from the wider field coverage. The inventory estimates that nitrogen fertiliser application is the single largest N2O source from the livestock farm accounting for 49% of annual emissions.

Fixed N (nitrate, nitrite, and ammonium) is a limiting nutrient for photosynthesis in the surface ocean. The rates and relative importance of N cycling processes, however, are temporally and spatially complex, which hamper their direct measurement and quantification. The South Atlantic subtropical front separates the Atlantic Ocean and the subantarctic, an area which can elucidate information about water masses both entering and leaving the basin. Through the GEOTRACES programme, an oceanographic section across 40°S in the South Atlantic is used to investigate biogeochemical cycling of nitrogen and carbon in this region. Hydrographic data, in combination with the isotopic composition of nitrate (NO3-), particulate organic carbon and particulate nitrogen (δ15NNO3, δ18ONO3, δ13CPOC, δ15NPN), is used to provide integrative measurements for temporally and spatially variable processes of the marine N-cycle and C-cycle. A thorough examination of the stable isotope cycling of particulate and dissolved N across the subtropical front is used to quantify the supply of fixed N to the mixed layer. The relative importance of nitrate from the subsurface, N2 fixation, terrestrial input and atmospheric deposition in supplying production is determined. Typically, 30-50% of the export flux in the subtropical water masses is sourced from N2 fixers and up to 75% within the Brazil Current. This finding suggests that diazotrophs may be abundant in the South West Atlantic providing a source of new N to this region. To assess the basin scale N-cycling processes, the deep water masses were analysed to reveal the origin and history of NO3-. Intermediate waters formed in the subantarctic are enriched in δ15NNO3 and δ18ONO3 from partial utilisation by algae. This enrichment in δ15NNO3 is not present in the subtropical North Atlantic or the return flow of the North Atlantic Deep Water (NADW), which decreases from ~5.9‰ in the newly formed intermediate waters to ~4.8‰ in the NADW at 40°S. The modification of isotopic signatures through the subtropical Atlantic can be calculated as an incorporation of 26-36 Tg N yr-1 of newly fixed N from an isotopic source of -1‰ (N2 fixation). The extent of N addition is higher than estimated rates of N loss within the Atlantic and surpasses the amount of N deficit supplied to the basin. Fixed N inputs and losses through the global ocean are investigated by the assessment of remineralised nitrate added to the ocean interior. A lower δ15N is observed in Atlantic remineralised nitrate in comparison to the Pacific. The relative importance of N2 fixation and pelagic denitrification within each ocean basin is quantified and through this approach, N2 fixation rates are estimated at 92-116 Tg N yr-1 in the Pacific and 24-32 Tg N yr-1 in the Indian Ocean. Combining Atlantic N2 fixation of ~32 Tg N yr-1 with Indo-Pacific, global N2 fixation rates can be estimated at 142-184 Tg N yr-1. The high inputs in the Pacific suggest that excess P is the dominant control on the success of N2 fixers. However, estimates of new N addition to the Atlantic indicate other mechanisms such as the recycling efficiency of P and supply of Fe to the surface ocean increase N2 fixation rates above this threshold. The organic matter supplied to sediments is principally derived from phytoplankton across the subtropical front. High organic content is associated with the productive Brazil-Malvinas Confluence region where a diverse supply of nutrients sustains elevated biomass. The Rio Plata outflow is characterised with high δ15NNO3 and δ15NPN, suggesting denitrification processes occur in the estuary. A low δ13C source associated with high Al concentrations is identified on the western slope, indicating a supply of terrestrial derived C to the deep ocean. The fractionation of C uptake by phytoplankton is assessed in subtropical and subantarctic waters. In the subantarctic, CO2[aq] and growth rates determine the extent of C isotope fractionation. In this region, low species diversity and a small range in cell size enable the fractionation from CO2[aq] and growth rate to be expressed in phytoplankton. In subtropical water masses a larger range of cell size is the principal determinant of C fractionation. Increased surface area to volume is the main mechanism for increasing C uptake, arguing against the use of δ13CPOC as a palaeoproxy. The low δ13CPOC and δ15NPN observed in the subtropics (from C fractionation and N2 fixation) contrast the heavier signatures in the subantarctic. These observations are propagated to the sediments, wherein organic matter shifts are determined by changes in the subtropical front over time. The results of this study have greatly improved knowledge of N and C cycling within the South Atlantic, providing new insight into the cycling of these two important elements in the surface and deep ocean, on a regional and global scale.

This thesis explores the ecology of a pre-contact Western Alaskan faunal assemblage, through a combination of zooarchaeological and stable isotope techniques. The permafrost-preserved assemblage was excavated in 2009/10 at Nunalleq (c. AD 1350-1700) on the Yukon-Kuskokwim Delta by the University of Aberdeen, in collaboration with Qanirtuuq Inc. and the Native village of Quinhagak. Zooarchaeological analysis was conducted to identify the species present at Nunalleq. Analysis of butchery marks suggested patterns of human utilization of faunal resources and data on the age profile of the assemblage provided information on the seasonality of hunting and site occupation. A wide range of marine, freshwater and terrestrial species was observed, with pinnipeds, dogs and caribou particularly frequent. Subsequently, stable isotope analysis (δ13C, δ15N and δ34S) was carried out on 20 species identified at Nunalleq. The application of carbon and nitrogen isotope analysis enabled investigation of the diets and habitats of the various species and their relative positions in the food-web. These data were compared with data from contemporaneous Alaskan sites and modern studies, allowing investigation of diachronic and geographical variability. The dogs, as the only domestic species found in the prehistoric North American Arctic with a unique role between the domestic and the wild, were the focus of an in-depth zooarchaeological and isotopic case study. The comparison of stable isotope data from humans and dogs revealed a similarity in diet and, together with osteological evidence for butchery, indicated the complex role of dogs in human subsistence strategies. Sulphur isotope analysis provided a complementary tool with which to explore isotope variability, and facilitated a consideration of its potential benefits in enhancing the more commonly-used combination of carbon and nitrogen analysis in the interpretation of faunal isotope ecology. The advantages of integrating zooarchaeological and stable isotope data are discussed and future research directions are explored.

Nitrogen (N) belongs among necessary elements for plant growth and development. In the past attention was paid mostly to the inorganic forms - nitrate and ammonium. In soil N is also present in organic forms, including proteins, for which plants could compete with soil microorganisms. Recently two ways have been considered - the hydrolysis of proteins by secreted proteases and endocytosis of native proteins, possibly their confluence. Tobacco plants were grown in vitro under sterile conditions in modified Murashige-Skoog medium with casein as the only source of N (CAS), decreased concentration of inorganic forms of N (AD) or in complete Murashige-Skoog medium as control plants (MS). After the 12 weeks growth, the standard growth parameters were measured. The CAS plants were able to grow without inorganic N, and protein content in the leaves was higher than in other experimental plants. Proteomic analysis documented differences in protein expression in plant roots in the dependence on the form of N. In total 185 proteins were identified, 75% of proteins were less and 14% more abundant in the CAS plants. The uptake of casein conjugated with fluorescein was followed and the proteolytic activity was analyzed by confocal microscopy. Among proteins secreted from roots to the medium aspartic protease...

The reactions of 4,6-dinitrobenzofuroxan, (DNBF) with aniline and six of its N- and ring- substituted derivatives have been studied. It is known that aniline usually reacts as a nitrogen nucleophile, forming nitrogen-bonded σ-adducts with trinitrobenzene, (TNB) in the presence of a strong base. However, in acidic solutions, a-adducts are formed with bonding between a ring carbon atom of the anilines and the 7-position of DNBF. A value of 2.0 for k(_H)/k(_D), the kinetic isotope effect, indicates that bond formation is largely rate determining in the substitution pathway. Estimates were made for the pK(_a) values relating to carbon protonation of the anilines. In solutions of aniline buffered with aniline hydrogen chloride it was possible to distinguish an initial, rapid reaction via the nitrogen centre to give anionic a-adducts. The thermodynamically more stable carbon-bonded σ-adducts were observed to form over time. In the presence of excess amine, these zwitterionic σ-adducts were in rapid equilibrium with the deprotonated forms. Equilibrium constants for this acid-base process were measured, and indicate that the negatively charged DNBF moiety is electron withdrawing relative to hydrogen. Kinetic and equilibrium studies are reported for the reactions of several aliphatic amines with a selection of nitrobenzofurazan derivatives in DMSO. Rapid reaction at the 5- position to yield σ-adducts was followed by slower formation of the thermodynamically more stable adducts at the 7-position. Proton transfer from the zwitterionic intermediates to a second molecule of amine was generally rapid, and the attack of the amine rate determining. This is in direct contrast with reactions involving TNB, where the proton transfer step is usually rate limiting. The reactions of four nitrobenzofurazan derivatives with sulfite have been studied in aqueous solutions. The stability of the initially formed 5-adducts was remarkably high in comparison with the corresponding σ-adducts formed from attack of sulfite on TNB. A slow isomerisation was observed to yield the thermodynamically more stable 7-adducts, except in the reaction with 4-nitro-7-chlorobenzofurazan, where attack at the 7-position would lead to nucleophilic substitution of the chloro-group to yield the substitution product. The mechanism of the isomerisation was found to occur via an intermolecular rearrangement, and not according to an intramolecular Boulton-Katritzky rearrangement. Sulfite attack on DNBF was also studied. A value for the equilibrium constant for the formation of a 1:1 adduct, K(_7) 1.1 x 10(^13) dm(^3) mol(^-1) was determined. This high value is a reflection of the high carbon basicity of the sulfite ion, and the highly electrophilic character of DNBF. Evidence was also obtained for the formation of 1:2 di-adducts in the presence of excess sulfite, which are present in the isomeric cis and trans forms.

Master of Science / Department of Agronomy / J. Anita Dille / Variable-rate (VR) nitrogen (N) applications have the potential to improve efficiency of grain sorghum production. Field experiments were conducted in 2010 and 2011 in Stockton and Manhattan, KS. Four VR-N prescriptions were generated using various combinations of grid soil sampling data, soil electrical conductivity (EC) data, and yield maps, and were compared in the field with a uniform application based on a composite soil sample and whole field average yield goal. Soil EC data were used to create management zones that were individually soil sampled. Prescriptions were applied before planting and grain sorghum was harvested and recorded with a yield monitor in the fall. Grain sorghum yields responded to N at both sites with a higher response in 2010 due to more precipitation during the growing season. At Stockton in both years, greatest yields and returns were realized with prescription 4, a combination of management zone soil data and spatially-variable yield goal, while the smallest yields were realized with prescription 2 based on management zone soil data and field average yield goal. Prescription 5, which used grid-soil sampling and a spatially-variable yield goal, and prescription 2 resulted in the lowest returns in both years. At Manhattan in both years, greatest yields and returns were realized with prescription 3, combining a composite soil sample with spatially-variable yield goal. Prescription 5 was among the lowest returning treatments in both years. At Stockton, there was no correlation between yield and soil EC during the 2010 growing season, however there was a significant correlation between yield and shallow EC during the drier 2011 season. At Manhattan, yield was correlated to deep EC in 2010 and to shallow EC in 2011. Overall, increasing spatial intensity of data to develop the prescriptions did not necessarily result in an increased yield response to the application. Prescriptions that included a variable yield goal component tended to perform better across both sites and years.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Jared Hoyle / Buffalograss [Buchloe dactyloides (Nutt.) Engelm] is a warm-season turfgrass species that is native to North America and requires minimal maintenance to survive. However, the use of buffalograss on golf courses throughout the transition zone is limited due to its appearance, growth habit, and lack of information available. Buffalograss is more drought tolerant than many other turfgrass species cultivated on golf courses, therefore, its drought resistance can lead to significant water savings. The objectives of these 2014 – 2016 field research studies were to evaluate: 1) buffalograss divot recovery as influenced by nitrogen source and application rate; 2) the influence of nitrogen application rate and simulated golf cart traffic on the wear tolerance of buffalograss; 3) the effect of simulated golf cart traffic on colorant treated buffalograss; and 4) buffalograss recovery from winter trafficking. When compared to untreated turf, divots in buffalograss treated with urea achieved 50% divot recovery 6.3 days faster when 1 lb N/1,000 ft² was applied, which was statistically similar to the 3 lb N/1,000 ft² rate. Applications of a slow-release polymer coated urea did not enhance divot recovery duration when compared to untreated turf. As nitrogen application rate increased in the presence of traffic stress, regardless of traffic rate, the green cover, quality, and color of the turf was enhanced. Percent green cover values for 0, 1, 2, and 3 lb N/1,000 ft² 10 weeks after initiation (WAI), regardless of traffic rate, were 60.2%, 69.0%, 75.5%, and 79.1% respectively. Regardless of nitrogen application rate, buffalograss receiving 16 passes/week of traffic never provided >72% green cover, while buffalograss receiving 0 passes/week had 74% green cover prior to the onset of dormancy. Endurant Premium turfgrass colorant in the presence of wear treatments provided >50% green cover 0 – 5 weeks after treatment in 2014 and 0 – 3 weeks in 2015. In general, as traffic rate increased, turfgrass colorant longevity decreased. Overseeded perennial ryegrass hindered buffalograss recovery after winter trafficking in comparison to untreated turf and colorant applications.

Call number: LD2668 .T4 1957 Z54 / Master of Science