Дисертації: "Nitrogen"

1

Mooleki, Siyambango Patrick. "Synchronization of nitrogen availability and plant nitrogen demand, nitrogen and non-nitrogen effects of lentil to subsequent wheat crops." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0029/NQ63902.pdf.

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2

Ritchie, Karl B. "Influences of Nitrogen Supply and Elevated CO2 on Nitrogen Consumption, Nitrogen Loss, Tissue Nitrogen Concentration, and Yield of Hydroponic Wheat." DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/6746.

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Wheat was grown hydroponically for 23 days ( early boot stage) in a controlled environment at NO3- concentrations of 100 and 1000 μ,M and CO2 levels of 360 and 1200 μ,mol mo1-1. Nitrogen consumption and transpiration were measured daily. Tissue nitrogen concentration, total biomass, and percent root mass were measured at harvest. Nitrogen recovery and nitrogen use efficiency were calculated. Elevated CO2 increased nitrogen consumption of the 100 μ,M NO3- treatment by 13.6% and the 1000 μ,M NO3- treatment by 21.3%. These increases were particularly evident during tillering and early grain fill. Whole plant nitrogen, shoot NO3-, and root NO3- concentrations were increased by elevated CO2. High CO2increased biomass by 15% and increased percent root mass by 11 %. Nitrogen recovery and nitrogen use efficiency were similar at both CO2 concentrations. Transpiration (L m-2ground d-1) decreased by 40% in elevated CO2. The 1000 μ,M NO3- treatment consumed more NO3- than did the 100 μ,M NO3- treatment (8.1% in ambient CO2, 15.5% in elevated CO2); this effect was most pronounced during the last 5 days of the experiment (flag leaf emergence and early grain fill). Percent root mass increased as N concentration decreased from 1000 to 100 μ,M. Nitrogen levels did not significantly affect tissue N concentration or biomass. Nitrogen losses increased as N supply increased; an average of 16% of the nitrogen added to the 100 μ,M NO3- treatment was lost, while the 1000 μ,M NO3- treatment lost 21%. Nitrogen use efficiency and transpiration were similar in both nitrogen treatments.

3

Farr, C. R. "Nitrogen Stabilizer Effect on Nitrate Nitrogen Management in Soils." College of Agriculture, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/204454.

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4

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.

5

Nilsson, Lino. "Nitrogen transformations at the Kiruna mine : The use of stable nitrogen isotopes to trace nitrogen-transforming processes." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-209419.

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Release of different nitrogen compounds can cause eutrophication in lakes and rivers whichcan lead to oxygen-free environments in bottom water and in the sediment and can in turnlead to fish-deaths. Ammonium can be toxic to biota and nitrate can in high concentrationeven be toxic to humans. WHO has released a limit for nitrate concentration in drinking waterof 10mg/l. The LKAB mine in Kiruna is the largest underground iron mine in the world and isprospecting, mining and refining iron ore, with an annual production of around 28 milliontons. Release of different nitrogen compounds as a result of the explosives used during themining operations has been a known problem for some time; however the processes affectingnitrogen during the water transport have never been fully investigated. The main objective of this MSc thesis is to determine if changes in nitrogen and oxygenisotope composition can be used as a tracer for nitrogen transformation processes in the minewater at LKABs underground mine in Kiruna. Water samples were collected at key points in the water transport system and were analyzedfor isotopic composition. Isotopic and chemical data revealed two different sources of nitrateand ammonium, undetonated explosives and leachate from waste rocks. Three differentnitrogen changing processes affecting concentration of nitrate and ammonium were found:ammonium volatilization, nitrification and sorption. It was not possible to quantify theseprocesses individually. No processes which decrease the nitrate concentration were found.

6

Goshima, H., T. Suzuki, N. Hayakawa, M. Hikita, and H. Okubo. "Dielectric breakdown characteristics of cryogenic nitrogen gas above liquid nitrogen." IEEE, 1994. http://hdl.handle.net/2237/6812.

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7

Brown, Tabitha Therisa. "Variable rate nitrogen and seeding to improve nitrogen use efficiency." Thesis, Washington State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10043121.

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Increased nitrogen (N) fertilizer additions to modern agricultural cropping systems will be necessary to feed a growing world population. However, greater nitrogen use efficiency (NUE) is required if agroecosystems are to continue to provide certain ecosystem services (e.g., greenhouse gas emission reductions and water quality goals). The aim of this research was to investigate the role of variable rate N and seeding of winter wheat (Triticum aestivum) for optimizing yield-water-NUE relationships across heterogeneous landscapes. Field plot studies were conducted at the Cook Agronomy Farm (CAF) near Pullman, WA during the 2010, 2011 and 2012 winter wheat harvest years. A randomized complete block split plot N rate x seeding rate experiment with N fertilizer rate as main plot and seeding rate as subplot was employed across three landscape positions. Assessed were evidence of “haying-off”, depletion of available water resources, and the link between yield, protein, and NUE response to landscape by N fertilization rate by seeding rate treatment combinations. A performance classification was developed to evaluate wheat performance with regard to N utilization efficiency (Gw/Nt) and N uptake efficiency (Nt/Ns) components of the NUE.

Evidence of haying-off in winter wheat was medium to high for drier landscape positions, particularly during low precipitation years and likely occurs in these landscapes most years. Treatment impacts on NUE varied by year and landscape but overall NUE decreased by 14 to 22 kg grain yield per kg N supply as N rate increased from 0 to 160 kg N ha^-1 across three landscape positions and two site years (2011 and 2012). Target NUE and maximum anthesis biomass could be achieved with a 34 to 68% reduction in typical seeding rates. The NUE-based performance classification was helpful in identifying environmental or management conditions contributing to low or high NUE indicating potential to be used as an evaluation tool. This research also included a policy fellowship focused on N₂O emission reductions and greenhouse gas offset credits that could be generated from adoption of variable rate N for wheat and concluded that offset credits alone would not provide enough incentive for adoption of variable rate N.

8

Aguilar, Michelle. "Ruminal Nitrogen Recycling and Nitrogen Efficiency in Lactating Dairy Cattle." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/76829.

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Excess nitrogen (N) excretion from animal agriculture results in reduced air and water quality, and poses a risk to human health. Although the dairy industry utilizes milk urea N (MUN) to monitor protein feeding and N excretion, phenotypic diversity among cows may influence MUN and thus bias feed management. An initial study using data from 2 previously published research trials and a field trial, observed that cow had a significant effect on MUN variation. Regression models, utilized to predict MUN, corrected for dietary nutrients and some animal effects, and thus the observed effect of cow on MUN variation may reflect genetic selection decisions of animals with either poor or efficient urea transport. A second trial observed that MUN and PUN concentrations were positively correlated with gut urea clearance, providing evidence for differences in urea transport activity among cows. The presence of urea transport variation suggests that current protein recommendations may not estimate true requirements. A third trial observed that animals fed sub-NRC levels of RDP and RUP had reduced N intake and excretion of fecal N, urinary urea-N, and MUN. Animals maximized N efficiency and had no loss in milk production, suggesting a possible overestimation of RDP and RUP in the current NRC prediction model. The present project provides evidence for phenotypic variation among cows, which may be partially explained by differences in urea transport activity. Future work confirming genetic variation among urea transporters may provide an opportunity to improve feeding management if cow urea efficiency is known.
Master of Science

9

Campana, Mariana [UNESP]. "Coletores de amônia, fontes e formas de aplicação de nitrogênio em Panicum maximum CV. Tanzânia submetido a manejo intensivo." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/95286.

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Made available in DSpace on 2014-06-11T19:27:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-01-12Bitstream added on 2014-06-13T20:17:00Z : No. of bitstreams: 1 campana_m_me_botfmvz.pdf: 694345 bytes, checksum: 5b95a0f43e56990d64086b8a724378b9 (MD5)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Universidade Estadual Paulista (UNESP)
Com objetivo de validar o uso no campo do coletor de espuma com ácido e politetrafluoroetileno que capta amônia volatilizada e quantificar essa perda oriunda de fontes e formas de aplicação de nitrogênio (N) em pastagens, realizou-se 2 experimentos. No experimento 1, para avaliação do coletor, utilizou-se fatorial 2 x 2 - doses de N (50 e 100 kg/ha) e coletores de amônia (coletor semi-aberto e absorvedor de espuma com ácido e politretafluoroetileno). O período experimental foi de 22 dias. No experimento 2 utilizou-se delineamento de blocos ao acaso e os tratamentos foram: uréia; Super N®; uréia + 12,5% de zeólita; uréia + 25% de zeólita; uréia + 50% de zeólita; uréia em pulverização foliar; 75% de uréia + 25% de sulfato de amônio; nitrato de amônio e sem N (testemunha). A avaliação das perdas por volatilização de amônia ocorreu em 3 épocas. No verão/07 e inverno/07 utilizou-se dose de 50 kg/ha de N para adubos sólidos e 15 kg/ha de N para pulverização foliar e para o verão/08 as doses foram duplicadas. As perdas diárias de amônia foram avaliadas em onze amostragens a cada dois dias para ambos os experimentos. Para o experimento 1, não houve diferença entre os coletores na perda acumulada e diária de amônia com a dose de 50 kg/ha de N. Entretanto, na dose de 100 kg/ha de N o coletor semi-aberto captou o maior pico de volatilização diária e maior acúmulo de amônia. No experimento 2 as menores perdas por volatilização foram detectadas para nitrato de amônio aplicado a lanço e uréia via pulverização foliar. Dessa forma poderia ocorrer melhor uso do fertilizante pela planta refletindo em aumento na produção e qualidade da forragem.
With the objective of validating the field use of the foam collector with acid and polytetrafluorethylene, which captures volatilized ammonia and quantify this loss when using sources and application forms of nitrogen (N) in pastures, 2 experiments were realized. In the experiment 1, to evaluate the collector a 2 x 2 factorial – N doses (50 and 100 kg/ha) and ammonia collectors (semi-open collector and foam absorber with acid and polytetrafluorethylene). The experimental period was 22 days. In the experiment 2, the experimental design was a randomized block design and the treatments were: urea; Super N®; urea + 12,5% of zeolite; urea + 25% of zeolite; urea + 50% of zeolite; urea leaf spraying, 75% of urea + 25% of ammonium sulfate, ammonium nitrate, and without nitrogen (control). The evaluation of the volatilization losses occurred in 3 periods. On summer/07 and winter/2007 a 50 kg/ha of N dose for solid fertilizers was used and a 15 kg/ha N dose for leaf spraying and on summer/2008 the doses were doubled. The daily losses of ammonia were evaluated in eleven samplings every two days for both experiments. In the experiment 1, there was no difference between the collectors in the accumulated and daily loss in the dose of 50kg/ha of N. However, with the dose of 100 kg/ha of N the semi-open collector showed the highest peak of daily volatilization and accumulated the highest volatilization loss. In the experiment 2, the lowest volatilization losses were detected for ammonium nitrate in soil application and urea in leaf spraying application. So, in this cases might happen the better use of the fertilizer by the plant, reflecting in the increase of the forage production and quality.

10

Barreto, Rafael Ferreira. "Interação entre silício e citocininas nas respostas do tomateiro à toxicidade de amônio /." Jaboticabal, 2019. http://hdl.handle.net/11449/182116.

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Orientador: Renato de Mello Prado
Coorientador: Rogério Falleiros Carvalho
Banca: Arthur Bernardes Cecilio Filho
Banca: Cid Naudi Silva Campos
Banca: Lucas Aparecido Gaion
Banca: Lilian Ellen Pino
Resumo: Uma consequência da toxicidade de amônio (NH4+) é a diminuição do conteúdo de citocininas (CKs). Dessa forma, o fornecimento de CK, na forma de trans-zeatina (tZ), pode aliviar a toxicidade de NH4+, e a CK sintética 6-benziladenina (BA), de menor custo, ainda não foi estudada quanto ao seu efeito sobre a toxicidade de NH4+. Além disso, o silício (Si), que é um elemento benéfico, é capaz de amenizar vários estresses, como a toxicidade de NH4+. Objetivou-se verificar se o alívio da toxicidade de NH4+ com o uso do Si é dependente do aumento do teor de CKs no tomateiro cv Micro-Tom (MT), os efeitos do Si no tomateiro transgênico MT CKX2 (baixo teor de CKs) submetido à toxicidade de NH4+ e se o regulador de crescimento BA alivia a toxicidade de NH4+ no tomateiro MT. Para isso, realizaram-se cinco experimentos em tomateiro, com a aplicação dos tratamentos na solução nutritiva. No experimento com concentrações de NH4+ entre 1,25 e 7,5 mmol L-1, 5,9 mmol L-1 provocou a toxicidade de NH4+, com diminiução de 10% na massa seca da parte aérea. No experimento com concentrações de Si entre 0,2 e 0,8 mmol L-1, na forma de silicato de potássio (SiK) ou ácido silícico estabilizado (ASiE), a toxicidade de NH4+ não foi aliviada. No experimento com concentrações de Si entre 1,0 e 2,5 mmol L-1, na forma de SiK, a concentração de 1,29 mmol L-1 de Si aliviou a toxicidade de NH4+. No experimento com N nas formas de NO3- ou NH4+ (5,9 mmol L-1), na ausência e na presença de Si (1,29 mmol L-1) no tomat... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: A consequence of ammonium (NH4+) toxicity is the decrease in cytokinins (CKs) content. However, the supply of CK in the nutrient solution, in trans-zeatin (tZ) form, can alleviate NH4+ toxicity, and CK synthetic 6-benzyladenine (BA), with lower cost, has not yet been studied on the NH4+ toxicity. Similarly, silicon (Si), which is a beneficial element known to relieve stresses, also alleviates NH4+ toxicity. The objective was to verify if the relief of NH4+ toxicity by Si is dependent on the increase of the CKs content in tomato cv Micro-Tom (MT), the effects of Si on the transgenic tomato MT CKX2 (CKs deficient) submitted to NH4+ toxicity, and if the growth regulator 6-benzyladenine (BA) alleviates NH4+ toxicity in tomato MT. For this, five experiments were carried in tomato, with treatments application in nutrient solution. In experiment with NH4+ concentrations between 1.25 and 7.5 mmol L-1, 5.9 mmol L-1 caused NH4+ toxicity, with shoot dry weight 10% decrease. In experiment with Si concentrations between 0.2 and 0.8 mmol L-1, via potassium silicate (SiK) or stabilized silicic acid (ASiE), NH4+ toxicity was not alleviated. In the experiment with Si concentrations between 1 and 2.5 mmol L-1, via SiK, the concentration of 1.29 mmol L-1 alleviated NH4+ toxicity. In experiment with N in NO3- or NH4+ forms (5.9 mmol L-1), in absence and presence of Si (1.29 mmol L-1) in MT tomato, Si decreased CKs content in root and increase in shoot, independent of the N form. In same experime... (Complete abstract click electronic access below)
Doutor

11

Wheildon, Andrew R. "Novel nitrogen chemistry." Thesis, University of Nottingham, 1999. http://eprints.nottingham.ac.uk/13326/.

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Chapter One contains a brief overview of zeolites, their structure, uses and synthesis. Chapter Two relates to the attempted synthesis of quinuclidines via a novel 6-endo-trig radical cyclisation. Chapter Three contains a review of the 'Zip reaction' and the attempted synthesis of triazacyclopentadecane derivatives. Chapter Four relates to the synthesis of pyrrolidines via retro-Cope cyclisation methodology. Reviews of the Cope and retro-Cope reactions, nitrone synthesis and nucleophilic addition of carbon nucleophiles to nitrones are included. The synthetic work is split into three sections relating to the electron withdrawing group used to stabilise the carbanion of the nucleophile - ester, sulphone and sulphoxide - and attempts to indicate the utility of the retro-Cope reaction in the diastereoselective synthesis of substituted pyrrolidines.

12

Shaw, Brian Andrew. "Nitrogen stabilized zirconias." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285404.

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13

Pamplona, Maria Teresa Troina. "Aromatic nitrogen mustards." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385254.

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14

Crowston, E. H. "Nitrogen dioxide oxidations." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37986.

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15

Stadler, Christina. "Nitrogen release and nitrogen use efficiency of plant derived nitrogen fertilisers in organic horticultural soils under glasshouse conditions." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980532159.

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16

Rafle, Abdirashid Dulane 1961. "NITRATE-NITROGEN AND TOTAL NITROGEN CONCENTRATION IN GRAIN SORGHUM (SORGHUM BICOLOR (L.) MOENCH) AS RELATED TO NITROGEN FERTILIZATION." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/291249.

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17

Forrester, David Ian, and davidif@unimelb edu au. "Mixed-species plantations of nitrogen-fixing and non-nitrogen-fixing trees." The Australian National University. Faculty of Science, 2005. http://thesis.anu.edu.au./public/adt-ANU20050202.164252.

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Mixed-species plantations of eucalypts and acacias have the potential to improve stand productivity over that of respective monocultures through the facilitative effect of nitrogen-fixation by acacias, and increased resource capture through above- and belowground stratification. However, growth in mixed-species plantations may not be improved compared to that of monocultures when competitive interactions outweigh the effects of improved nutrient availability and resource capture. Careful selection of sites and species is therefore critical to successfully improving stand productivity using mixed-species plantations. This study set out to examine some of the processes and interactions that occur in mixed-species plantations, and the effect nutrient and water availability can have on the growth of mixtures. In three out of four mixed-species field trials examined in this study, growth was not increased in mixtures compared to monocultures. However, in the fourth field trial, heights, diameters, stand volume and aboveground biomass were higher in mixtures of E. globulus and A. mearnsii from 3-4 years after planting. The range in outcomes from mixing species in these four trials shows that a fundamental understanding of the underlying processes is required to enable a greater predictive capacity for the circumstances under which mixtures will be successful. Therefore the growth dynamics, processes and interactions were examined in the mixtures of E. globulus and A. mearnsii. The difference in productivity between mixtures and monocultures in this trial increased with time up to age 11 years, when 1:1 mixtures contained twice the aboveground biomass of E. globulus monocultures. The positive growth response of trees in mixture compared to monocultures was the result of accelerated rates of nutrient cycling, a shift in C allocation and reductions in light competition through canopy stratification. Nitrogen contents of foliage and soil clearly showed that A. mearnsii influenced the N dynamics in this trial. If these changes in N contents were due to N fixation by A. mearnsii, then about 51 and 86 kg N ha-1 yr-1 was fixed in the 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation was also examined using the natural abundance method. The delta15N values of foliage collected at 10 years were grouped according to the mycorrhizal status of the host plant. Therefore the discrimination of 15N during transfer from mycorrhizae to the host plant appeared to vary with mycorrhizal status, and the natural abundance of 15N was not used to quantify N fixation. Rates of N and P cycling in litterfall were significantly higher in stands containing at least 25% A. mearnsii (more than 31 kg N ha-1 yr-1 and more than 0.68 kg P ha-1 yr-1) compared to E. globulus monocultures (24 kg N ha-1 yr-1 and 0.45 kg P ha-1 yr-1). Rates of litter decomposition and N and P release were about twice as high in 1:1 mixtures compared to E. globulus monocultures and were even higher in A. mearnsii monocultures. It is therefore important to select N-fixing species that are capable of cycling nutrients quickly between the plant and soil, and that have readily decomposable litter. The total belowground C allocation was not significantly different between mixtures and monocultures (14 to 16 Mg C ha-1 yr-1). However, since aboveground net primary production was greater in 1:1 mixtures, the changes in nutrient availability appears to have increased total productivity (both above- and belowground), and reduced the proportion of C allocated belowground in mixtures compared to E. globulus monocultures. In a pot trial containing mixtures of E. globulus and A. mearnsii both species grew larger in mixture than in monoculture at low N levels, and mixtures were more productive than monocultures. However, at high N levels, E. globulus suppressed A. mearnsii and mixtures were less productive than E. globulus monocultures. Similar effects were found for high and low levels of P. Therefore resource availability can have a strong influence on the interactions and growth of mixtures. The productivity of mixtures may only be increased on sites where the resource for which competition is reduced in mixture is a major limiting growth resource. For example, if N is not a limiting growth factor then an increase in N availability from N-fixation may not increase growth, and the N-fixing species may compete for other resources such as soil P, moisture or light. This study has shown that mixtures containing a N-fixing trees and a non-N-fixing trees can be more productive than monocultures, but that this increase in productivity will only occur on certain sites. Examination of the growth, interactions and processes that occurred in mixtures in this study provide useful information that can aid the selection of species combinations and sites.

18

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.

19

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.

20

Lernbecher, Vincent. "Swedish Nitrogen Flows : A national budget of anthropogenically induced reactive nitrogen." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289176.

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Nitrogen is a fundamental element in all forms of life and a crucial component of our agricultural productivity and global food security. However, excess nitrogen caused by human activity poses a serious threat to the environment and human health. Understanding human influences on the nitrogen cycle are therefore essential for sustainable management of the nutrient. The flows of anthropogenically influenced and created reactive nitrogen in Sweden are examined in this study. Human-induced sources and mechanisms associated with nitrogen are quantified and illustrated in several charts constructed with material flow analysis (MFA) methodology. Swedish society is divided into sectors of agriculture, industry, consumption, and waste management and the quantified nitrogen flows interacting with each system are used to highlight areas of interest. Results show considerable impacts stemming mainly from the food system, starting with agricultural use of mineral and organic fertilizer. Emissions of ammonia to air from animal husbandry and leakage of nitrogen to waterways are the biggest losses in the agricultural sector. The driving force behind the large agricultural losses is first and foremost the consumption pattern of households. Emissions of nitrogen oxides from traffic and industrial processes also make up a large part of the total nitrogen load. The recovery rate of nutrients that ultimately end up in the waste sector is relatively low and most of the nitrogen is denitrified in wastewater treatment plants.
Kvävgas i form av N2 finns i överflöd i jordens atmosfär. Cirka 78% av luften är i själva verket N2. För att levande organismer ska kunna använda det atmosfäriska kvävet måste den först brytas ned och bindas till antingen väte, kol eller syre. I sin reaktiva form fungerar elementet som en grundläggande byggsten för alla levande varelser. Den naturliga processen som förvandlar oanvändbart atmosfäriskt kväve till dess reaktiva former kallas kvävefixering och utförs av bakterier. I ekosystemet avgör därmed tillgängligheten av reaktivt kväve vegetationens tillväxt och är därmed en begränsande faktor för jordbruket. Denna begränsning upphörde med uppfinningen av industriell kvävefixering i form av Haber-Bosch processen där ammoniak utvinns ur luften. Sedan dess har miljontals ton av reaktivt kväve införts till den naturliga kvävecykeln och orsakat störningar med allvarliga konsekvenser. I Sverige började arbetet med att reducera överskottet av reaktivt kväve på allvar under 1980-talet då näringsinnehållet i Östersjön redan hade överskridit hållbara nivåer. Sedan dess har ny lagstiftning som behandlar frågan införts både på nationell nivå och på EU- nivå. Insatserna har påverkat minskningen av kväveöverskottet, men många belastningsgränser överskrids fortfarande. För att samordna strategier och lagstiftning kring den komplexa kvävecykeln och ytterligare begränsa miljöbelastningen krävs en mer integrerad, holistisk strategi och ett gemensamt ramverk. Denna studie skapades med detta i åtanke och med målet att öka medvetenheten om kvävets belastning på miljön. I studien kvantifierades mänskligt inducerade källor och mekanismer associerade med kväve och illustrerades i flera diagram konstruerade med en materialflödesanalys (MFA) metod. Det svenska samhället är indelat i fyra sektorer: jordbruk, industri, konsumtion och avfallshantering. De resulterande kväveflödena används sedan för att lyfta fram intressanta områden och skapa en översiktsbild. Resultaten visar betydande flöden som huvudsakligen härrör från livsmedelssystemet, med början i jordbruksanvändning av mineral- och organisk gödselmedel. Utsläpp av ammoniak till luft från djurhållning samt läckage av kväve till vattendrag utgör de största förlusterna i jordbrukssektorn. Den drivande kraften bakom det stora inflödet av gödselmedel och orsaken till jordbruksförlusterna är först och främst hushållens konsumtionsmönster. Utsläpp av kväveoxider från trafik och industriprocesser utgör även en stor del den totala kvävebelastningen. Återvinningsgraden av näringsämnen som slutligen hamnar i avfallssektorn är relativt låg och majoriteten av kvävet denitrifieras i reningsverk. Slutsatsen är att det nuvarande tillståndet för antropogent kväveflöde i Sverige är linjärt och att nytt kväve kontinuerligt måste tillföras till systemet.

21

Asih, A. Rai Somaning. "Nitrogen utilization and production of dairy goats fed different nitrogen sources /." St. Lucia, Qld, 2001. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16142.pdf.

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22

Funkey, Carolina P. "Abiotic Release of Low Molecular Weight Nitrogen from Effluent Organic Nitrogen." W&M ScholarWorks, 2011. https://scholarworks.wm.edu/etd/1539617906.

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23

Forrester, David Ian. "Mixed-species plantations of nitrogen-fixing and non-nitrogen-fixing trees." Connect to this title online, 2004. http://thesis.anu.edu.au/public/adt-ANU20050202.164252/.

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24

Thompson, Astrid M. "Enchytraeids and nitrogen : the effects of nitrogen on enchytraeid populations and the influence of enchytraeids on nitrogen translocation in soil." Thesis, Durham University, 2005. http://etheses.dur.ac.uk/1288/.

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25

Haig, Paul Andrew. "Effect of dietary nitrogen solubility on nitrogen losses from lactating dairy cows." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ43169.pdf.

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26

Ring, Eva. "Nitrogen in soil water at five nitrogen-enriched forest sites in Sweden /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 2001. http://epsilon.slu.se/avh/2001/91-576-5795-5.pdf.

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27

Tomaszewski, Timothy Edward. "Atmospheric nitrogen deposition at a conifer forest: Canopy nitrogen uptake and photosynthesis." Diss., Connect to online resource, 2006. 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:3219013.

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28

Bhogal, Anne. "Effect of long-term nitrogen applications on nitrogen cycling under continuous wheat." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294731.

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29

Warren, G. P. "Available nitrogen in relation to fractions of soil nitrogen in grassland soils." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370367.

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30

Earl, Stevan Ross. "Nitrogen spiraling in stream ecosystems spanning a gradient of chronic nitrogen loading." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11284.

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This dissertation is a study of the relationships between nitrogen (N) availability and spiraling (the paired processes of nutrient cycling and advective transport) in stream ecosystems. Anthropogenic activities have greatly increased rates of N loading to aquatic ecosystems. However, streams may be important sites for retention, removal, and transformation of N. In order to identify controls on NO3-N spiraling in anthropogenically impacted streams, I examined relationships among NO3-N spiraling and a suite of chemical, physical, and biological variables in streams spanning a gradient of N concentration. Across all streams, gross primary production (GPP) accounted for most NO3-N demand. Uptake of NO3-N was also related to GPP but was limited by N availability when N concentrations were low. A combination of GPP and NO3-N explained 80% of the variance in uptake. In chapter 3, I conducted a series of short-term nutrient releases in which streamwater NO3-N concentration was incrementally elevated to identify conditions leading to saturation of uptake capacity. Four of six study streams showed signs of N limitation whereas there was no significant change in uptake with increasing NO3-N amendment in two streams, suggesting N saturation. Proximity to saturation was generally correlated to N concentration but was also predicted by the ratio of N:P. My results suggest complex relationships between N spiraling and availability that depend on resident biota and other limiting factors. In chapter 4, I examined nutrient spiraling methodology by comparing differences between ambient and amendment-derived NO3-N spiraling metrics. I quantified spiraling metrics during a short-term NO3-N amendment and under ambient conditions using a stable isotope (15NO3-N) tracer. Uptake lengths measured during amendments were consistently longer than ambient uptake lengths. Amendment-derived NO3-N uptake velocity and uptake were underestimated relative to ambient conditions. Using a technique to estimate ambient uptake length extrapolated from the relationship between uptake length and nutrient amendment concentration for a series of amendments at different concentrations, I found that extrapolated uptake lengths were generally better predictors of ambient uptake lengths than amendment-derived uptake lengths but the technique was less effective in high N streams that showed signs of weak N limitation.
Ph. D.

31

Cui, Jian. "Synthesis and characterization of new boron-nitrogen and boron-nitrogen-phosphorus systems." [Fort Worth, Tex.] : Texas Christian University, 2009. http://etd.tcu.edu/etdfiles/available/etd-03162010-123538/unrestricted/Cui.pdf.

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32

Norton, Eric R., and Jeffrey C. Silvertooth. "Evaluation of the Effects Added Nitrogen Interaction on Nitrogen Recovery Efficiency Calculations." College of Agriculture, University of Arizona (Tucson, AZ), 1999. http://hdl.handle.net/10150/197255.

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Two studies were conducted in 1996 and 1997 at the University of Arizona Maricopa Agricultural Center (MAC) to evaluate the added nitrogen interaction (ANI) or ‘priming effect’ on the determination of nitrogen recovery efficiencies (NRE). The method employed was to compare NRE’s as calculated by two different methods; the difference technique and the isotopic technique. The difference in NREs observed between the two methods indicates the extent of an ANI. Results demonstrated no statistical differences between NRE’s calculated by the two methods. Therefore, no ANI was observed in the field. These results indicate that the less expensive method of calculating NREs (difference technique) is sufficient under irrigated cotton production systems in the desert Southwest.

33

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.

34

Kakkar, Avneet. "Nitrogen Availability and Use Efficiency in Corn Treated with Contrasting Nitrogen Sources." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6886.

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The plant-soil nitrogen cycle plays a significant role in allocation of available N to plants, and improved understanding of N cycling helps sustainably increase fertilizer use efficiency. There are various processes (nitrogen mineralization and nitrification) involved in the availability and mobility of nitrogen in the soil. The primary objective of this study was to determine the NUE under contrasting nitrogen treatments over a period of five years. Additionally, we examined the effect of different N treatments on N mineralization and nitrification in conventional and organic farming systems. This project was funded by Agriculture and Food Research Initiative Competitive Grants Program Grant no. 2011-67019-30178 from the USDA National Institute of Food and Agriculture and by the Utah Agricultural Experiment Station. We established silage corn field plots in northern Utah, and silage corn was grown using ammonium fertilizers or manure composts over five years. Nitrogen use efficiency was found to be higher in ammonium sulfate fertilizer treatments as compared to compost treated soils. Nitrogen mineralization and nitrification rates were examined for soils from the silage corn field plots and also for additional soils from certified organic field plots receiving steer compost, steer manure and crop rotations. There was a significant overall nitrogen treatment effect for both conventional and organic rotational plots. Carbon mineralization rates were found to be higher in compost under conventional plots and manure under organic rotational plots as compared to control. There was no significant treatment effect found in gross mineralization and nitrification rates in 2015 and 2016. Gross nitrification rates were found to be the higher in AS200 treatment versus compost and control in 2016. Improved knowledge of the timing and rates of nitrogen supply is vital for improving NUE and for reducing excessive use of fertilizers while maintaining an acceptable yield. The optimization of fertilizer rates according to crop demand at different stages of growth will be helpful in the efficient management of available N especially for composts and manures.

35

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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36

Hemmings, Philippa Rachel. "Nitrogen heterocycles from sugars." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314823.

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37

Campbell, Elizabeth M. "Nitrogen assimilation by limpets." Thesis, University of Glasgow, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479100.

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38

Slater, Jonathan. "Cyclometallated nitrogen heterocycles - metallomesogens." Thesis, University of Warwick, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269196.

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39

Michori, Peter K. "Nitrogen budget under coffee." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333405.

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40

Qaddo, Akram. "Enantiospecific nitrogen heterocycle synthesis." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/15791/.

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41

Supeno, Carleton University Dissertation Chemistry. "Sonochemical fixation of nitrogen." Ottawa, 2000.

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42

Georgiou, George Cleovoulos. "Nitrogen-rich oximic complexes." Thesis, London Metropolitan University, 1988. http://repository.londonmet.ac.uk/3051/.

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43

Fathi, Ghodratollah. "Nitrogen responsiveness in barley." Title page, table of contents and abstract only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phf2524.pdf.

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44

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.

45

Cody, Michael Jonathan. "Cycling nitrogen for productivity in agroforestry, nitrogen, lignin and polyphenol controls on mineralization." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40039.pdf.

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46

Pask, Alistair. "Optimising nitrogen storage in wheat canopies for genetic reduction in fertiliser nitrogen inputs." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/12567/.

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Firstly, increasing true stem RN capacity as means to increase the maximum rate of N uptake (kg N per day) during stem elongation may be feasible through optimisation of traits such as stem length and wall thickness. Secondly, modifying true stem RN unloading by increasing storage N in relation to accumulation N may offer a realistic mechanism for improving crop BPE and thus UTE. Such an increase in true stem NRE might be achieved through manipulation of key N assimilation enzymes. Thirdly, it may be possible to select for ‘stay-green’ traits associated with lower leaf lamina NRE and lower grain N% to boost UTE. However, in each case further phenotyping studies are required to characterise genetic variability, identify the most appropriate germplasm resources for genetic studies, and to identify appropriate genetic sources of variation for breeding.

47

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.

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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.

48

Saunders, Eleanor Margaret. "The effect of mineral nitrogen on ectomycorrhizas with special reference to nitrogen deposition." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299547.

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49

Meakins, Tracey Suzanne. "The influence of dietary nitrogen intake on urea-nitrogen salvage in the colon." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243079.

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50

Lorentz, Laura J. "Hyperspectral Reflectance and Stable Isotopic Nitrogen: Tools to Assess Forest Ecosystem Nitrogen Cycling." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51214.

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The use of nitrogenous fertilizers in agricultural and forestry practices coupled with increased fossil fuel combustion and resulting nitrogen (N) deposition across the landscape have contributed to a near doubling of N inputs to terrestrial ecosystems. With such dramatic changes have come adverse environmental consequences including the acidification of soil and water resources and an increased rate of biodiversity loss in both flora and fauna. A method of rapidly predicting ecosystem susceptibility to N loss across large spatial scales would facilitate the identification of those systems most likely to contribute to potentially adverse environmental impacts. To begin the development of such a framework, this research utilizes study sites located throughout the geographic ranges of Douglas-fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) to explore relationships between hyperspectral remote sensing, N stable isotope ratios ("15N) and growth response to nitrogenous fertilizer. In both species multiple linear regression models relating leaf-level reflectance to "15N showed strong predictive capabilities, with some models explaining more than 65% of the variance in "15N. Significant correlations between "15N metrics and growth response to N fertilization were also observed in both species. Additional exploratory analysis of the inclusion of "15N metrics with other environmental and edaphic variables to predict fertilizer growth response showed an increase in model performance with the addition of the enrichment factor (EF ="15NFol - "15NSoil). This research demonstrates the ability of hyperspectral reflectance to predict "15N and reveals the potential of "15N to be included in future models to predict fertilizer growth response.
Master of Science

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