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1
Xu, Zhihong, and n/a. "Nitrogen Cycling in Leucaena Alley Cropping." Griffith University. Division of Australian Environmental Studies, 1991. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050906.155955.
Full textAbstract:
Field experiments were conducted on an Alfisol in the semi-arid tropics of northern Australia to investigate nitrogen (N) cycling in the leucaena (Leucaena leucocephala) alley cropping system. This is a farming system in which maize (Zea mays L.) is grown in alleys formed by leucaena hedgerows spaced 4.5 metres apart. Mineralization of N from Ieucaena (prunings) and maize residues was studied under field conditions. Response of maize growth to addition of N fertilizer and plant residues was evaluated both in field plot and microplot experiments. The fate of fertilizer N and leucaena N was examined over four consecutive seasons. The decomposition (loss of mass) of dry, cut 15N-labelled leucaena residues differed from that of intact fresh leucaena prunings in the first cropping season although no difference was detected after one year. At the end of one cropping season, 3 months after application, 58-72% of 15N-labelled leucaena had decomposed compared to only 34-36% of fresh leucaena prunings. Similar trends occurred at 20 and 52 days after application. The extent of decomposition of fresh leucaena prunings (28-33%) was similar at two loading rates (2.4 and 4.7 t DM ha -1) by 3 months after addition. About 72% of young 15N labelled maize residues was decomposed by 3 months after addition in the presence of fresh leucaena prunings. Decomposition of 15N-labelled leucaena residues and unlabelled fresh prunings was 91% and 88% respectively 14 months after addition. After 2 years the corresponding values were 96% and 94%. When N content of the recovered residues was taken into account, the values were 95% and 94% after 14 months, and the same (97%) after 2 years. Maize yield and N uptake were significantly increased following addition of either unlabelled fresh leucaena residues or 15N-labelled thy Ieucaena residues. Application of N ferilizer produced a thither increase in the presence of the residues. The maize yield and N uptake with the 15N-labelled leucaena were not different from those with the unlabelled residues. There was a significant positive interaction between N fertilizer and leucaena prunings which increased maize production. Addition of maize residues decreased the yield and N uptake of maize compared with that obtained in the presence of N fertilizer at 40 kg N ha~1 and leucaena residues (2.4 t DM ha-1). There was a marked residual benefit of N fertilizer applied in the first season at 36 kgN hat in the presence of leucaena prunings on the second maize crop yield and N uptake, but not on the third crop. However, a significant residual benefit of leucaena prunings added in the first season was found in DM yield and N uptake of the second and third maize crop. The short-term fate of 15N applied in plant residues was examined during two separate cropping seasons. By 20 days after application of separate 15N-labelled leucaena leaves, stems and petioles, 3-9% of the added 15N could be found in maize plants, 33-49% was in surface residues, 36-48% in the 2 m soil proffle and 0.3-22% unaccounted for. In a separate experiment when leucaena components were not separated, 5% of 15N applied in leucaena residues was taken up by maize 52 days after addition, 45% was in residues, 25% was in soil and 25% was unaccounted for. Jn another experiment, maize recovered 6% of added leucaena 15N after 2 months, 39% remained in residues, 28% was in soil and 27% was not recovered. Incorporation of 15N-labelled leucaena residues in the soil did not increase recoveiy of leucaena 15N by maize compared with placement of the residues on the soil surface. By the end of one cropping season (3 months after application), 9% of added 15N was recovered by maize from 15N-labelled leucaena. There was a similar 15N recoveiy from 15N-labelled maize residues applied as mulch at 1.7 t DM ha1 together with unlabelled leucaena prunings at 2.4 t DM ha ~. In both cases, 30-32% of added 15N was detected in soil, 28% in residues, and 31-34% apparently lost. The short-term fate of fertilizer 15N was different from that of 15N added in plant residues. In a 52-day experiment, maize recovered 65-79% of fertilizer 15N applied at low rates (6.1 and 12.2 kg N ha -1) in the presence of leucaena prunings, 21-34% was present in soil, and less than 1% was not recovered. By 2 months after application, recoveiy of fertilizer 15N by maize was 41% from N fertilizer added at 80 kg N ha -1, 35% from N fertilizer at 40 kg N ha -1 in the presence of leucaena prunings, and 24% from N fertilizer at 40 kg N ha -1 in the presence of maize residues and leucaena prunings. The corresponding deficits (unaccounted-for 15N) were 37%, 38% and 47% respectively. A small but significant amount of the fertilizer 15N was present in the unlabelled leucaena residues (3%) and in the mixture of unlabelled leucaena and maize residues (7%) present on the soil surface. However, application of the plant residues did not affect recoveiy of the fertilizer 15N in soil (21-24%). When N fertilizer was applied at 40 kg N hi1 in the presence of leucaena prunings, 43% of fertilizer 15N was recovered by maize at the end of cropping season, 20% in soil, 2% in residues, and 35% unaccounted for. The long-term fate of fertilizer 15N was compared with that of leucaena 15N in an experiment over four cropping seasons. In the first season, maize tops recovered 50% of the fertilizer 15N but only 4% of the leucaena 15N. In the second, third and fourth seasons, maize (tops + roots) recovered 0.7%, 0.4% and 0.3% of the initial fertilizer 15N compared with 2.6%, 1.8% and 1.4% of the initial leucaena 15N. In the second, third and fourth seasons, recovery of the initial fertilizer 15N (12-14%) in soil was much lower than that of the initial leucaena 15N (38-40%). There was no further loss of the fertilizer 15N after the first season. However, the cumulative 15N deficit for the leucaena 1N in the first two seasons was 50%--thissuggested an additional loss of 23% since the end of the first season. There was no further loss of 15N from either residual fertilizer 15N or residual leucaena 15N in the third and fourth seasons. In conclusion, application of leucaena prunings could substantially increase maize yield and N uptake although some supplementary N fertilizer may be required to achieve maximum crop yield. Maize recovered only a small amount of added leucaena N in the first year. Most of the leucaena residue N was present in the soil and remaining residues after one season. This residue N would be gradually available for plant uptake by subsequent crops. Of course, annual additions of leucaena prunings would appreciably increase the pool of available N over time. Thus, application of leucaena prunings could substantially improve soil fertility in the long term.
2
Xu, Zhihong. "Nitrogen Cycling in Leucaena Alley Cropping." Thesis, Griffith University, 1991. http://hdl.handle.net/10072/365424.
Full textAbstract:
Field experiments were conducted on an Alfisol in the semi-arid tropics of northern Australia to investigate nitrogen (N) cycling in the leucaena (Leucaena leucocephala) alley cropping system. This is a farming system in which maize (Zea mays L.) is grown in alleys formed by leucaena hedgerows spaced 4.5 metres apart. Mineralization of N from Ieucaena (prunings) and maize residues was studied under field conditions. Response of maize growth to addition of N fertilizer and plant residues was evaluated both in field plot and microplot experiments. The fate of fertilizer N and leucaena N was examined over four consecutive seasons. The decomposition (loss of mass) of dry, cut 15N-labelled leucaena residues differed from that of intact fresh leucaena prunings in the first cropping season although no difference was detected after one year. At the end of one cropping season, 3 months after application, 58-72% of 15N-labelled leucaena had decomposed compared to only 34-36% of fresh leucaena prunings. Similar trends occurred at 20 and 52 days after application. The extent of decomposition of fresh leucaena prunings (28-33%) was similar at two loading rates (2.4 and 4.7 t DM ha -1) by 3 months after addition. About 72% of young 15N labled maize residues was decomposed by 3 months after addition in the presence of fresh leucaena prunings. Decomposition of 15N-labelled leucaena residues and unlabelled fresh prunings was 91% and 88% respectively 14 months after addition. After 2 years the corresponding values were 96% and 94%. When N content of the recovered residues was taken into account, the values were 95% and 94% after 14 months, and the same (97%) after 2 years. Maize yield and N uptake were significantly increased following addition of either unlabelled fresh leucaena residues or 15N-labelled thy Ieucaena residues. Application of N ferilizer produced a thither increase in the presence of the residues. The maize yield and N uptake with the 15N-labelled leucaena were not different from those with the unlabelled residues. There was a significant positive interaction between N fertilizer and leucaena prunings which increased maize production. Addition of maize residues decreased the yield and N uptake of maize compared with that obtained in the presence of N fertilizer at 40 kg N ha~1 and leucaena residues (2.4 t DM ha-1). There was a marked residual benefit of N fertilizer applied in the first season at 36 kgN hat in the presence of leucaena prunings on the second maize crop yield and N uptake, but not on the third crop. However, a significant residual benefit of leucaena prunings added in the first season was found in DM yield and N uptake of the second and third maize crop. The short-term fate of 15N applied in plant residues was examined during two separate cropping seasons. By 20 days after application of separate 15N-labelled leucaena leaves, stems and petioles, 3-9% of the added 15N could be found in maize plants, 33-49% was in surface residues, 36-48% in the 2 m soil proffle and 0.3-22% unaccounted for. In a separate experiment when leucaena components were not separated, 5% of 15N applied in leucaena residues was taken up by maize 52 days after addition, 45% was in residues, 25% was in soil and 25% was unaccounted for. Jn another experiment, maize recovered 6% of added leucaena 15N after 2 months, 39% remained in residues, 28% was in soil and 27% was not recovered. Incorporation of 15N-labelled leucaena residues in the soil did not increase recoveiy of leucaena 15N by maize compared with placement of the residues on the soil surface. By the end of one cropping season (3 months after application), 9% of added 15N was recovered by maize from 15N-labelled leucaena. There was a similar 15N recoveiy from 15N-labelled maize residues applied as mulch at 1.7 t DM ha1 together with unlabelled leucaena prunings at 2.4 t DM ha ~. In both cases, 30-32% of added 15N was detected in soil, 28% in residues, and 31-34% apparently lost. The short-term fate of fertilizer 15N was different from that of 15N added in plant residues. In a 52-day experiment, maize recovered 65-79% of fertilizer 15N applied at low rates (6.1 and 12.2 kg N ha -1) in the presence of leucaena prunings, 21-34% was present in soil, and less than 1% was not recovered. By 2 months after application, recoveiy of fertilizer 15N by maize was 41% from N fertilizer added at 80 kg N ha -1, 35% from N fertilizer at 40 kg N ha -1 in the presence of leucaena prunings, and 24% from N fertilizer at 40 kg N ha -1 in the presence of maize residues and leucaena prunings. The corresponding deficits (unaccounted-for 15N) were 37%, 38% and 47% respectively. A small but significant amount of the fertilizer 15N was present in the unlabelled leucaena residues (3%) and in the mixture of unlabelled leucaena and maize residues (7%) present on the soil surface. However, application of the plant residues did not affect recoveiy of the fertilizer 15N in soil (21-24%). When N fertilizer was applied at 40 kg N hi1 in the presence of leucaena prunings, 43% of fertilizer 15N was recovered by maize at the end of cropping season, 20% in soil, 2% in residues, and 35% unaccounted for. The long-term fate of fertilizer 15N was compared with that of leucaena 15N in an experiment over four cropping seasons. In the first season, maize tops recovered 50% of the fertilizer 15N but only 4% of the leucaena 15N. In the second, third and fourth seasons, maize (tops + roots) recovered 0.7%, 0.4% and 0.3% of the initial fertilizer 15N compared with 2.6%, 1.8% and 1.4% of the initial leucaena 15N. In the second, third and fourth seasons, recovery of the initial fertilizer 15N (12-14%) in soil was much lower than that of the initial leucaena 15N (38-40%). There was no further loss of the fertilizer 15N after the first season. However, the cumulative 15N deficit for the leucaena 1N in the first two seasons was 50%--thissuggested an additional loss of 23% since the end of the first season. There was no further loss of 15N from either residual fertilizer 15N or residual leucaena 15N in the third and fourth seasons. In conclusion, application of leucaena prunings could substantially increase maize yield and N uptake although some supplementary N fertilizer may be required to achieve maximum crop yield. Maize recovered only a small amount of added leucaena N in the first year. Most of the leucaena residue N was present in the soil and remaining residues after one season. This residue N would be gradually available for plant uptake by subsequent crops. Of course, annual additions of leucaena prunings would appreciably increase the pool of available N over time. Thus, application of leucaena prunings could substantially improve soil fertility in the long term.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Division of Australian Environmental Studies
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3
Roberts, J. Murray. "Nitrogen cycling in the Anemonia viridis symbiosis." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360160.
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4
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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5
Ngai, Zoology. "Trophic effects on nutrient cycling." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2851.
Full textAbstract:
The top-down effects of consumers and bottom-up effects of resource availability are
important in determining community structure and ecological processes. I experimentally
examined the roles of consumers — both detritivores and predators — and habitat context in
affecting nutrient cycling using the detritus-based insect community in bromeliad leaf wells. I
also investigated the role of multiple resources in limiting plant productivity using meta analyses.
The insect community in bromeliads only increased nitrogen release from leaf detritus in
the presence of a predator trophic level. When only detritivores were present, the flow of stable
isotope-labeled nitrogen from detritus to bromeliads was statistically indistinguishable from that
in bromeliads lacking insects. I suggest that emergence of adult detritivores constitutes a loss of
nitrogen from bromeliad ecosystems, and that predation reduces the rate of this nutrient loss.
Hence, insects facilitate nutrient uptake by the plant, but only if both predators and detritivores
are present. Moreover, predators can affect nutrient cycling by influencing the spatial scale of
prey turnover. This mechanism results in a pattern opposite to that predicted by classic trophic
cascade theory.
Increasing habitat complexity can have implications for nutrient cycling by decreasing
the foraging efficiency of both predators and their prey, and by affecting the vulnerability of
predators to intraguild predation. Along a natural gradient in bromeliad size, I found that,
depending on the relationship between community composition and habitat size, habitat
complexity interacts with the changing biotic community to either complement or counteract the
impact of predators on nutrient uptake by bromeliads.
In contrast to the existing emphasis on single-resource limitation of primary productivity,
meta-analyses of a database of 653 studies revealed widespread limitation by multiple resources,
and frequent interaction between these resources in restricting plant growth. A framework for
analyzing fertilization studies is outlined, with explicit consideration of the possible role of
multiple resources. I also review a range of mechanisms responsible for the various forms of
resource limitation that are observed in fertilization experiments.
These studies emphasize that a wider range of predator and nutrient impacts should be
considered, beyond the paradigm of single resource limitation or classic trophic cascades.
6
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.
Full textAbstract:
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.
7
Grantley-Smith, M. P. "Nitrogen cycling in growing cattle fed maize silage." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370353.
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8
Malone, Edward Thomas. "Development of nitrogen cycling in recently deglaciated watersheds." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5338/.
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Perturbation of natural environments through anthropogenic nitrogen (N) inputs and climate change significantly alter soil systems. Few pristine environments remain in which to study natural controls on the development of soil N cycling over time and thus increase our understanding of the natural development of such mechanisms. This study took place in Glacier Bay National Park and Preserve (GBNP), southeast Alaska. This area presented a unique opportunity to study microbial cycling in near pristine soil systems. Six river catchments were selected for study across a chronosequence of 200 years of primary succession. Within each watershed soil nutrient content and microbial processes where evaluated to determine a time frame for development. Samples were collected from riparian and wider catchment areas in order to investigate the effects of dominant vegetation types and slope steepness. These data were coupled with percent vegetation type generated by analysis of satellite imagery allowing the scaling up of soil variables. A key finding of this research was that vegetation type is the primary influence on nitrogen cycling processes and soil characteristics. With increasing age potential microbial activity increased in particular nitrification, which linked with the low soil NO\(_3\)- indicated a large heterotrophic microbial community in older soils.
9
Hall, Cynthia Adia. "Insights into marine nitrogen cycling in coastal sediments." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28228.
Full textAbstract:
Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.Committee Chair: Ellery Ingall; Committee Member: Andrew Stack; Committee Member: Greg Huey; Committee Member: Joseph Montoya; Committee Member: Judith Curry.
10
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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11
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.
Full textAbstract:
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
12
Nave, Lucas Emil. "Nitrogen cycling in the northern hardwood forest soil, plant, and atmospheric processes /." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196187071.
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13
Rosales, Villa Alida. "Insight into the nitrogen cycling in the North Sea." Thesis, University of East Anglia, 2016. https://ueaeprints.uea.ac.uk/61021/.
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Fixed nitrogen (N) is an important element which may limit marine primary production. Nitrogen inputs to coastal waters have increased putting pressure on this ecosystem. Supply and removal of N depends on a series of N-cycling processes including canonical denitrification and anammox which remove N, while dissimilatory nitrate reduction to ammonium (DNRA) recycles N allowing it to remain available for primary producers. The sediments in the coastal zone are a key site for these processes but the environmental factors regulating them are still poor understood and the fluxes poorly quantified. This study investigated sedimentary N-cycling at 5 sites in the open North Sea in August 2013, and at one station in the Wash estuary in May, June, September and October 2013 using 15N tracer techniques, pore water studies and direct sediment flux measurements. All sites had relatively low sedimentary organic carbon content (<5%). The results of this study showed temporal variation in the Wash, and spatial variation in the North Sea and the tracer studies provided valuable new information about the sedimentary nitrogen cycle. At all sites the main process contributing to total N2 production was denitrification (>95%) with on average >80% associated with coupled denitrification. The average rates of denitrification were higher in the North Sea (7.62 mol m-2h-1) than in the Wash (4.4 mol m-2h-1). Anammox was not detected at the Wash sites and contributed only 6.6% to total N2 production at the North Sea sites. DNRA was observed during three of the months studied at the Wash sites but only at one North Sea site and, where measurable, was responsible for between. 6.5 and 30% of nitrate reduction. Temperature was identified as an important control on the overall rates of denitrification. The results indicate that denitrification is a major sink for nitrate in the North Sea.
14
Clark, Benjamin Richard. "Plant control of nitrogen cycling : ecological and evolutionary consequences." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420981.
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Prior, Hannah. "Total nitrogen and total phosphorus cycling in riparian ecosystems." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285963.
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16
Kemmitt, Sarah Jane. "Effects of pH on nitrogen cycling in agricultural soils." Thesis, Bangor University, 2002. https://research.bangor.ac.uk/portal/en/theses/effects-of-ph-on-nitrogen-cycling-in-agricultural-soils(4d4c1c3d-6650-4eb6-bcac-7aadbda17631).html.
Full textAbstract:
This thesis reports a series of experiments performed to investigate the effects of soil pH on mineralisation processes in agricultural soils. The experiments utilised a short term soil incubation assay which measured the mineralisation of a mixture of 15 uniformly 14C labelled amino acids to 14CO2• Amino acids were chosen to represent the labile pool of dissolved organic matter and their mineralisation provides a means of comparing the activity of the soil microbial population performing mineralisation of nitrogenous substrates. An examination of mineralisation in five profiles of acidic soils (chapter 4) showed that the rate of amino acid mineralisation decreased with depth and was correlated significantly and linearly with total C and total N within each profile. The profiles examined contained high levels of nitrate suggesting the presence of significant populations of acid tolerant nitrifying bacteria. A strong positive correlation between basal respiration rate and the rate of amino acid mineralisation was demonstrated within most profiles. A study investigating the impact of varying intensities of sheep grazing from three upland regions of the UK on soil mineralisation processes was undertaken (chapter 5). This showed that the soil microbial biomass was maximal at low to intermediate levels of grazing across the three regions and declined as the legacy of grazing was reduced through the long term removal of sheep. High intensity of grazing tended to reduce the phenotypic evenness (a component of diversity) of the microbial community. Net mineralisation rates were highest in mid-successional and lightly grazed treatments in all regions and were generally lowest at the extremes of grazing influence. However, the rate of amino acid mineralisation was generally lowest in the short-term ungrazed and lightly grazed treatments and were fastest at the highest grazing pressure in all regions, supporting the model that heavily grazed grassland favours fast nutrient cycles dominated by labile substrates. Multiple regression of data from all sites showed that the impact of grazing on the activity of the SMB that actively mineralises nitrogenous substrates appears to function primarily through its effect on soil pH. A field study was conducted to investigate the feasibility of decreasing nitrate leaching in cereal and grass plots by acidification of soil (chapter 6). The results from porous ceramic cup extracted soil water showed that nitrate concentrations in drainage water were greater in cereal plots than in grass plots. Soil acidification lowered nitrate concentrations in drainage water, substantially over winter and spring in grass plots and in cereal plots the effect was minimal during winter but became more substantial in spring. Data indicates that soil acidification decreased nitrification rates, causing the ammonium pool to accumulate. Soil acidification also lowered levels of dissolved organic nitrogen in soil water, usually to a greater degree in grass than in cereal plots. It was concluded that it may be possible to use careful soil pH management as a tool to control nitrate leaching without compromising the quality of drainage water, this may be more effective on grassland than on arable crops. Long term experimental plots from Rothamsted Experimental Station, Woburn Experimental Farm and the Scottish Agricultural College Craibstone Estate were sampled to investigate the effect of soil pH on a range of microbially mediated soil mineralisation characteristics and processes (chapter 7). The results showed that soil pH did not significantly affect indigenous mineral nitrogen levels at the time of sampling and had little consistent effect on levels of soluble organic nitrogen or carbon across soil types. Soil pH also did not show any great influence on net ammonification, net nitrification or net total mineralisation in a 30 d aerobic incubation. Soil pH was positively correlated with soil microbial biomass carbon and nitrogen and soil basal respiration in each soil type. The proportions of organic C and N that were biomass C and N were positively correlated to soil pH, indicating an increase in availability of the C and N present in the soil with rising pH. Glucose-C and urea-C mineralisation rates were fastest at intermediate points of the pH range studied in each soil type. Arginine-C mineralisation was positively and linearly related to soil pH. Results of chapters 5, 6 and 7 showed that soil pH had a significant impact on the rate of amino acid mineralisation. Acidity increased the proportion of added amino acid-C used in respiration and decreased the proportion used in biomass, implying an acidity-induced stress on the microbial population. Soil microbial biomass C or N, basal respiration rates, total soil C and N and dissolved organic C and N were shown not to adequately predict the rate of amino acid mineralisation over the range of soil types studied. Suggestions for further investigations into the soil pH effects on characteristics of organic substrates and how they may determine carbon and nitrogen cycling rates are made.
17
Li, Renssheng. "Nitrogen cycling in young mine soils in Southwest Virginia." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39924.
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Deficiency of available nitrogen (N) is one of the major factors limiting the establishment of a long term self-sustaining vegetative community on mine soils. This investigation was conducted to study the nature of N form and dynamics in southwest Virginia mine soils.
Fresh mine spoils contained a large amount of indigenous N, ranging from 650 to 2500 mg/kg soil, which complicated N studies. Most of the indigenous N was "geologic N" which was unavailable to plants. The geologic N came from either 2:1 silicate minerals (fixed NH₄+) or coal fragments (nonhydrolyzable organic N). Active N, consisting of hydrolyzable organic N and exchangeable N, comprised the minor fraction of indigenous N available to plants.Ph. D.
18
Li, Jinling. "Effects of Biosolids on Carbon Sequestration and Nitrogen Cycling." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/49585.
Full textAbstract:
Land application of biosolids has been demonstrated to improve nutrient availability (mainly N and P) and improve organic matter in soils, but the effects of biosolids on C sequestration and N cycling in the Mid-Atlantic region is not well understood. The objectives were: 1) to investigate soil C sequestration at sites with a long-term history of biosolids either in repeated application or single large application; 2) to characterize and compare soil C chemistry using advanced 13C nuclear magnetic resonance (NMR) and C (1s) near edge x-ray absorption fine structure (NEXAFS) spectroscopic techniques; and 3) to compare biosolids types and tillage practices on short-term N availability in the Coastal Plain soils. Biosolids led to C accumulation in the soil surface (< 15 cm) after long-time application in both Piedmont and Coastal Plain soils. The C saturation phenomenon occurred in Coastal Plain soils, thus additional soil C accumulation was not achieved by increasing C inputs from biosolids to the Coastal Plain. Soil organic C from profiles in the field sites was not different at depths below the plow layer (15-60 cm). The quantitative NMR analyses concluded that O-alkyl C was the dominant form in the particulate organic matter (POM), followed by aromatic C, alkyl C, COO/N-C=O, aromatic C-O, OCH3 / NCH and ketones and aldehydes. The aliphatic C and aromatic C were enriched but the O-alkyl C was decreased in the biosolids-amended soils. The changes indicated that the biosolids-derived soil C was more decomposed and, thus, more stable than the control. The NEXAFS spectra showed that O-alkyl C was the dominant form in the POM extracted from biosolids-amended soils, followed by aromatic C, alkyl C, carboxylic C and phenolic C groups. These results were similar to those from NMR analysis. The regression and correlation analyses of C functional groups in the POM between NEXAFS and NMR indicated that both techniques had good sensitivity for the characterization of C from biosolids-amended soils. To evaluate short-term biosolids N availability, a three-year field study to investigate the effects of lime-stabilized (LS) and anaerobically digested (AD) biosolids on N availability in a corn-soybean rotation under conventional tillage and no-tillage practices was set up in 2009-2011. Results showed that both LS and AD biosolids increased spring soil nitrate N, plant tissue N at silking, post-season corn stalk nitrate N, grain yield, and soil total N by the end of the growing season. The same factors used to calculate plant available N for incorporated biosolids can be used on biosolids applied to no-till systems in coarse-textured soils. All these results indicated that the application of biosolids affects the long-term quantification and qualification of soil organic C and also improve short-term N availability in the Mid-Atlantic region.Ph. D.
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Yamashita, Tamon. "Nitrogen cycling in soil ecosystems of temperate coniferous plantations." Kyoto University, 2005. http://hdl.handle.net/2433/145441.
Full textAbstract:
Kyoto University (京都大学)0048
新制・論文博士
博士(農学)
乙第11586号
論農博第2546号
新制||農||902(附属図書館)
学位論文||H17||N3990(農学部図書室)
22885
UT51-2004-U483
京都大学大学院農学研究科熱帯農学専攻
(主査)教授 武田 博清, 教授 東 順一, 教授 谷 誠
学位規則第4条第2項該当
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Waddill, Dan W. "Nitrogen cycling in tall fescue turf with added clippings." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07212009-040500/.
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Noppe, Philip Alan 1959. "Nitrogen cycling at Emerald Lake watershed, Sequoia National Park." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/192018.
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An annual nitrogen balance was used to develop a conceptual model of nitrogen cycling at the 120 ha Emerald Lake watershed. Atmospheric loadings of NO₃⁻ (7200 eq) and NH₄⁺ (6800 eq) from snow represent the largest external nitrogen sources. Approximately 75 percent of the annual nitrate mass flux is transported by the first 40 percent of the annual lake inflow. The sum of NO₃⁻ and NH₄⁺ deposited from the atmosphere (21,000 eq) and released by soil mineralization (40,000 eq) exceeds inflow mass flux (8,000 eq). Denitrification (10,000 - 20,000 eq) and plant uptake may account for this difference. NH₄⁺ deposition (10,000 eq) and mineralization release (26,500 eq) are large, but the NH₄⁺ inflow flux is near zero. This difference may be due to nitrification with subsequent denitrification, or plant uptake. Data gaps preclude calculation of an annual overall acidity affect. Nitrification is a potential seasonal source of acidity.
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Soomro, Zaheer Ahmed. "Cycling of dissolved organic nitrogen in plant-soil systems." Thesis, Bangor University, 2014. https://research.bangor.ac.uk/portal/en/theses/cycling-of-dissolved-organic-nitrogen-in-plantsoil-systems(698c6c22-9cac-4493-8c5b-43f8a5d482ec).html.
Full textAbstract:
Poor availability of nutrients commonly constrains crop production in marginal environments of developing countries. Degraded soils and poor access to fertilizers limit the yields that can be produced by resource-poor farmers. In such circumstances, farmers need to use management techniques that maximize nutrient use efficiency of their crops. There are various techniques available, such as the use of legumes in crop mixtures or rotations, or careful placement and timing of fertilizer applications. In low-input agriculture the direct uptake of dissolved organic N (DON) by plants may be extremely important. DON represents a significant pool of soluble N in most ecosystems. Some plants may possess a greater capacity to take up DON rather than dissolved inorganic N (DIN). DON is composed of many compounds which enter soil from a range of sources (e.g. litterfall, root and microbial exudation, turnover of roots and organisms, urine and faeces, organic fertilizers). My aim was to investigate the impact of plant residues on DON cycling when incorporated into soils and to study the uptake of DON in comparison with DIN by the plant root system. In addition, the secondary aim was to investigate the influence of the rhizosphere on the transformation DON in soil. In the first trial, three experimental treatments were used to alter organic inputs: (1) Soil amended with straw (high C/N ratio), (2) Soil amended with grass residues (low C/N ratio), and (3) Non-amended (control). Results indicated that soil solution N03- and NH4+ accumulated in the grass-amended soil in contrast to that amended with straw or in the unamended control soil. Overall, straw immobilized DIN in solution. DON in the grass amended soil increased from day 14 to 21 and sharply decreased thereafter whilst the straw amended soil and control remained relatively constant. Contrary to expectation, the results indicate that addition of organic matter did not cause a large rise in DON relative to that of DIN. This suggests that in this high fertility agricultural soil the microorganisms rapidly break down DON contained in N rich organic residues to DIN. For N poor residues DON appears to represent a more important source of N, however, its availability to plants remains as yet unknown.
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Warren, Melissa. "Interactions between nitrogen fixation and methane cycling in boreal peat bogs." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53620.
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Microbial nitrogen (N2) fixation supplies important nitrogen inputs to boreal peatlands, extremely oligotrophic ecosystems dominated by Sphagnum mosses. In this study, we coupled major and trace nutrient analyses and rate measurements to characterize interactions between N2 fixation and CH4 cycling at the S1 peat bog in Marcell Experimental Forest and the Zim bog (Minnesota, USA). Total dissolved inorganic nitrogen (NO3-+NO2-+NH4+) and phosphate were both consistently < 2 μM in the porewater of surface peat, indicating severe nutrient limitation. While dissolved Fe was fairly abundant (18-35 mM), Mo, V and Cu were scarce (2-40 nM), suggesting that alternative metalloenzymes containing Fe in place of other metals may be favored. Rates of diazotrophy measured by both 15N2 incorporation and the acetylene (C2H2) reduction assay (ARA) were 7-fold higher under anoxic vs. oxic incubations conducted at both 4°C and 25°C. No significant difference in N2 fixation rates measured by either method was observed with or without the amendment of 1% CH4 at 25 °C; however, a significant inhibitory effect by methane was seen at 4°C in material from the S1 bog hollows. Anoxic 15N2 incorporation was 3-4x higher in treatments lacking acetylene, suggesting that the ARA likely underestimates N2 fixation by inhibiting diazotrophs sensitive to C2H2. Aerobic methanotrophy was also inhibited by 1% C2H2 when incubated under oxic conditions. No observations for the production of ethane (C2H6) were detected during the ARA, a biomarker for alternative nitrogenase activity. Major differences in ARA rates were observed to vary locally within microhabitats and between two bogs. In June 2014, peat sampled from hollows incubated under anoxic conditions showed the highest ARA rates (94.9 ± 11.0 nmol C2H4 g-1 moss dry mass hr-1), while the lowest rates were observed in
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hummock samples incubated under oxic conditions (5.1 ± 0.8 nmol C2H4 g-1 moss dry mass hr-1) in the S1 bog (T3 site). Observed rates have the potential to be a function of oxygen concentrations and or water content. ARA rates in all microcosm treatments were significantly lower at Zim bog compared to the S1 bog. The developed conversion factor between the regression of 15N2 and ARA in this study was 3.9 and agrees with the theoretical conversion factor as well as previous studies of soils and forest mosses.
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Crook, Hannah D. "Carbon and nitrogen cycling in upland wetlands : impacts of changing climate and atmospheric nitrogen deposition." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412169.
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Newton, Jennifer Denise. "Evidence for manganese-catalyzed nitrogen cycling in salt marsh sediments." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04072006-133610/.
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Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006.Taillefert, Martial, Committee Chair ; Ingall, Ellery, Committee Member ; DiChristina, Thomas, Committee Member.
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Shelford, Emma Joyce. "Influence of bacterial viruses on nitrogen cycling in the ocean." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/48494.
Full textAbstract:
Current studies indicate that viruses of marine bacteria are biological carbon sinks, transforming bacterial carbon into dissolved organic matter, the majority of which is respired rather than incorporated back into biomass. In contrast, this dissertation focusses on viruses, not as a carbon sink but as a catalyst of nitrogen cycling, benefiting phytoplankton by liberating nitrogen from bacterial lysates that would otherwise be tied up in bacterial biomass. The results in this dissertation show that organic nitrogen released by viral lysis of heterotrophic marine bacteria is remineralised by uninfected bacteria, and the resulting ammonium taken up by phytoplankton.
In an initial laboratory experiment, only a portion of the amino acids derived from heterotrophic bacterial lysates could be taken up by other heterotrophic bacteria within the duration of the experiment. Both D- and L-amino acids were taken up in proportion to their initial concentrations, demonstrating a lack of preference for the generally more labile L-amino acids. In a subsequent field experiment, reduction of the viral fraction in a marine microbial community resulted in reduced ammonium remineralisation and phytoplankton abundance, suggesting that remineralised nitrogen from bacterial metabolism of viral lysates contributes to phytoplankton growth. Another experiment added a marine bacterium labeled with 15N and infected with a lytic virus to microbial communities. This experiment directly demonstrated that remineralised nitrogen from bacterial lysates released through the action of viruses was a significant source of nitrogen for phytoplankton. In a final series of experiments, viruses were reduced from seawater from 22 field stations using bacterial concentration techniques to explore correlations between environmental factors and ammonium remineralisation from viral lysis. Viral mediated ammonium remineralisation changed with different chlorophyll a concentrations and salinities, suggesting potential predictive associations.
These results show that liberated nitrogen from viral lysis of bacteria is readily degraded by heterotrophic marine bacteria and remineralised into ammonium for uptake by autotrophic organisms. The results in this dissertation demonstrate that viruses are key players in the cycling of nitrogen in marine systems and stress the need to incorporate viral mediated nutrient release into models of global biogeochemical cycling.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Southwell, Melissa W. Martens Christopher S. "Sponges impacts on coral reef nitrogen cycling, Key Largo, Florida." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,756.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree Doctor of Philosophy in the Department of Marine Sciences." Discipline: Marine Sciences; Department/School: Marine Sciences.
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Bosch, Jennifer Anne. "Polychaetes, Hypoxia, and Nitrogen Cycling in the Mesohaline Chesapeake Bay." Thesis, University of Maryland, College Park, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3644071.
Full textAbstract:
Benthic macrofauna can play an important role in facilitating some of the microbial mediated processes of nitrogen cycling in estuarine sediments. Declines in benthic macrofauna, like polychaete worms, have been attributed to long-term increases in bottom water hypoxia in Chesapeake Bay. Utilizing a large monitoring dataset including benthic macrofaunal abundance, biomass, and concurrent measures of environmental parameters, I examined how environmental conditions regulate the densities of opportunistic polychaetes in a mesohaline estuarine system. This analysis points to a benthic community dominated by euryhaline, opportunistic polychaete worms (M. viridis, S. benedicti, H. filiformis, A. succinea) which have well adapted but varying responses to hypoxia and other stressful conditions. Results of two laboratory experiments with the opportunistic polychaete Alitta (Neanthes) succinea were used to quantify the short-term influence of density and size of surface-feeding polychaetes on sediment-water fluxes of inorganic nitrogen under varying oxygen conditions. Polychaete enhancements of O2 and nitrogen fluxes were strongly correlated with total animal biomass. Solute fluxes were stimulated by presence of both larger and smaller worms, but per capita effects were greater for the deep-burrowing larger polychaetes. Utilizing a unique large-scale monitoring dataset collected in the Chesapeake Bay, I employed Classification and Regression Tree (CART) and multiple linear regression (MLR) analyses to assess the relationship between benthic biomass and NH4 + efflux within different regions of the estuary by season. In addition to labile organic matter, oligohaline and mesohaline tributary temperature and salinity control the rate of nitrogen cycling and benthic macrofaunal biomass. In deeper regions of mesohaline tributaries and the mainstem Bay, dissolved oxygen was found to be the dominating parameter regulating sediment nitrogen pathways as well as the structure of the benthic macrofaunal community. With increased macrofaunal biomass, spring regressions indicated an enhancement of NH4+ efflux. In contrast, fall regressions indicated the enhancement of fixed nitrogen removal from sediments. Summer data lacked a significant relationship, but high NH4 + effluxes under hypoxic/anoxic conditions suggested dissolved oxygen is the primary driver of summer nitrogen cycling. This study, using field and laboratory data, concludes that a complex balance between seasonal and regional dissolved oxygen, temperature and salinity conditions shape not only the benthic community but also the relationship between macrofaunal biomass and sediment nitrogen flux in this eutrophic estuarine system.
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Nilsson, Lino. "Nitrogen Cycling at Cold Climate Mine Sites in Northen Sweden." Licentiate thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59661.
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High nitrogen discharge from mining sites has been an environmental issue that has been closely studied in the recent years. The environmental effects of high nitrogen discharge are mainly eutrophication, but can also lead to changed species composition and algae blooms. Nitrogen is a highly abundant element and is the most abundant element in the atmosphere, where 78% by volume is present as dinitrogen (N2 ). Nitrogen is present in reduced form in all organic life as ammonium (NH4 + ). Nitrogen is also present in reduced form as nitrate (NO3 - ) or nitrite (NO2 - ) in most aquatic systems. Both nitrate and ammonium is contributing to eutrophication problems worldwide and ammonia (NH3 ) is direct toxic in high concentration to certain sensitive aquatic species. Nitrate in high concentration is also direct toxic, both to humans but also to aquatic biota. To trace and quantify different nitrogen transforming processes, their sources and their sinks is called tracing nitrogen cycling and is important due to the environmental effect of nitrogen. Nitrogen is available in many different species and oxidation states which all have their respective geochemistry. This thesis focuses on tracing the complex nitrogen cycle in two different cold climate mining systems in northern Sweden using two different methods. The two studied systems are: The LKAB underground iron ore mine in Kiruna Boliden Minerals AB open pit copper ore mine Aitik outside Gällivare Two different approaches were used to trace the nitrogen cycling. The LKAB Kiruna mine was investigated using stable nitrogen isotopes. The isotope analysis showed high capability to trace nitrogen cycling, both quantative and qualitative. We also showed the origin of the isotope signals which gives indication to the different sources of nitrogen in the mine. The presented study shows presence of nitrification, ammonium volatilization and ammonium adsorption to waste rock to occur in the water transport system. The nitrogen cycling in the Boliden Aitik mine was investigated using a nitrogen model which we developed as part of this thesis. The model is based on Yakushevs Redox Layer model (ROLM). The model contains the state variables ammonium, nitrate, nitrite, plankton, phosphate, dead organic material (both particulate and dissolved) as well as oxygen. The nitrogen concentrations in the Boliden Aitik mine was modeled for the clarification pond and showed, in general, low biological activity. The biological mediated reactions such as nitrification, denitrification, phytoplankton growth and grazing were low in relation to natural lake systems
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ZILIUS, Mindaugas. "THE ROLE OF COMMON MACROFAUNA HOLOBIONTS IN BENTHIC NITROGEN CYCLING." Doctoral thesis, Università degli studi di Ferrara, 2021. http://hdl.handle.net/11392/2487836.
Full textAbstract:
Nei sistemi di estuario, le interazioni tra microrganismi e la macrofauna sono probabilmente ampiamente diffuse e possono stabilirsi attraverso molteplici meccanismi. La macrofauna, oltre a pascolare, bioturbare i sedimenti e ventilare le tane, può ospitare o e fare da vettore di microrganismi nell'ambiente circostante. La macrofauna e i microrganismi ad essa associati formano olobionti, ovvero unità biologiche e funzionali in grado di eseguire più processi. Tuttavia, essi sono in gran parte poco studiati a causa di limitazioni metodologiche o di un'eccessiva semplificazione degli approcci sperimentali. Pertanto, gli effetti cumulativi degli olobionti sono raramente presi in considerazione negli studi biogeochimici e la loro effettiva entità può essere sottovalutata quando si valutano i processi a livello di ecosistema.
In questa tesi, abbiamo studiato il contributo della macrofauna più rappresentata nei sedimenti bentonici di estuari poco profondi, con particolare enfasi sul ruolo delle interazioni ecologiche tra i microbi e i loro ospiti invertebrati sulla regolazione dei processi del ciclo dell'azoto (N). Abbiamo utilizzato una combinazione di approcci ecologici, biogeochimici e molecolari per suddividere il ruolo diretto e indiretto della macrofauna, comprese le attività di bioturbazione, fisiologiche e degli olobionti negli habitat bentonici.
I risultati mostrano che tutti gli olobionti della macrofauna ospitavano microbiomi attivi e complessi, capaci di diverse trasformazioni di N come la denitrificazione, la riduzione dissimulativa dei nitrati ad ammonio e la fissazione dell’azoto. Il rilevamento di trasformazioni di N in comuni olobionti della macrofauna evidenzia effetti nascosti e interattivi tra microbi e animali. Nel sistema di estuari tropicali abbiamo evidenziato una intensa attività di azoto fissazione da parte degli olobionti del granchio violinista, tale da superare le perdite di N per denitrificazione e da costituire una sorgente significativa di ammonio e N organico per l'ambiente circostante. Al contrario, il ruolo degli olobionti nei sistemi estuariali temperati e boreali è risultata di minore importanza rispetto all'attività delle comunità microbiche associate ai sedimenti. In tali ambienti, vari gruppi della comunità macrobentonica hanno evidenziato una alterazione del metabolismo bentonico e del ciclo dell'N, direttamente influenzando i tassi di respirazione ed escrezione e indirettamente tramite l’alterazione fisica del sedimento.
I risultati ottenuti supportano ulteriormente la tesi che i principali processi biogeochimici nei sedimenti sono prevalentemente il risultato degli effetti collettivi di diversi gruppi funzionali e delle loro mutue interazioni con i microbi associati. Sebbene il ruolo degli olobionti nei sistemi più freddi sia risultato relativamente basso rispetto a quello riscontrato negli ecosistemi tropicali, rimane da chiarire se ciò sia una costante o un quadro variabile da stagione a stagione. In futuro, ulteriori studi dovrebbero affrontare i fattori ambientali o biologici che regolano l'attività degli olobionti attraverso il condizionamento esercitato sui diversi taxa macrobentonici e nei diversi habitat.In estuarine systems, interactions between microbes and macrofauna are likely widespread and may establish through multiple mechanisms. Macrofauna, besides grazing, bioturbating sediments and ventilating burrows, can host or inoculate microbes from ambient environment. Macrofauna hosts and their associated microbes form holobionts, which are biological and functional units capable of performing multiple processes. However, they are largely understudied due to methodological limitations or oversimplification of experimental approaches. Therefore, the cumulative effects of holobionts are rarely accounted for in biogeochemical studies and their actual magnitude may be underestimated when assessing ecosystem-wide processes. In this thesis, we investigated the contribution of common macrofauna in shallow estuarine benthic sediments with emphasis on the role of ecological interactions between microbes and their invertebrate hosts on regulation of nitrogen (N) cycling processes. We used a combination of ecological, biogeochemical, and molecular approaches to partitioning the direct and indirect role of macrofauna including bioturbation, physiological and holobionts activities in benthic habitats. The results show that all macrofauna holobionts hosted active and complex microbiomes, capable of different N transformations, such as denitrification, dissimulative nitrate reduction to ammonium, and dinitrogen fixation. The detection of N transformations in common macrofauna holobionts highlights hidden and interactive effects among microbes and animals. In tropical estuarine system, abundant fiddler crab holobionts are a net dinitrogen (N2) sink, with N2 fixation exceeding N losses, and as a significant source of ammonium and dissolved organic N to the surrounding environment. On the contrary, the role of the holobionts in the temperate and boreal estuarine systems were of minor importance as compared to the activity of sediment-associated microbial communities. There, distinct macrofauna taxa in community altered benthic metabolism and N cycling directly by impacting respiration and excretion rates and indirectly by reworking sediment. The findings in this thesis further support that main biogeochemical processes in sediment are predominantly the result of the collective effects of different functional groups and their mutual interactions with associated microbes. Although the role of holobionts in colder systems was relatively low to this found in tropics, however this might be different along seasons or habitats. In the future, more studies should address environmental or biological factors that regulate holobionts activity across different taxa of macrofauna and habitats.
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Masse, Jacynthe. "Nitrogen cycling processes and microbial communities in reconstructed oil-sands soils." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58378.
Full textAbstract:
Covering 140,200 square km, the Athabasca Oil Sands deposit in Alberta is one of the largest single oil deposits in the world. Following surface mining, companies are required to restore soil-like profiles that can support the previous land capabilities. The overall objective of this thesis was to measure, compare and understand processes underlying nitrogen cycling rates and microbial communities in 20- to 30- year-old reconstructed oil-sands soils and in natural boreal-forest soils. The use of ¹⁵N tracer methods in combination with massively parallel sequencing techniques of the 16S and ITS genes identified key dissimilarities between reconstructed and natural boreal-forest soils. In reconstructed soils, NH₄⁺ was mainly cycled through the recalcitrant organic-N pool. In natural soils, NH₄⁺ was produced from the recalcitrant organic-N pool, but predominantly consumed in the labile organic-N pool, suggesting greater prominence of microbial N-cycling activity in the natural soils compared to the reconstructed soils. Reconstructed soils also produced more NO₃- than they immobilized it resulting in net nitrification rates. Prokaryotic and fungal β-diversity, but not α-diversity, differed between reconstructed and natural forest soils. Microorganisms associated with a copiotrophic lifestyle were more abundant in reconstructed soils, whereas microorganisms associated with an oligotrophic lifestyle were more abundant in natural forest soils. Vegetation cover was the main factor influencing prokaryotic and fungal α-diversity in reconstructed and natural forest soils. Nitrogen deposition, pH, soil nutrient content and plant cover influenced prokaryotic and fungal β-diversity. The results of this thesis deepen our understanding of the distinct pedological environments of oil-sands reconstructed soils and highlighted the importance of above- and below-ground interactions in reconstructed and natural ecosystems.Forestry, Faculty of
Graduate
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Schoenholtz, Stephen Hanley. "Restoration of nitrogen and carbon cycling in an Appalachian mine spoil /." This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-07282008-135352/.
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Walne, A. W. "A modelling study of nitrogen cycling in the Firth of Clyde." Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358856.
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Neubacher, Elke. "Oxygen and nitrogen cycling in sediments of the southern North sea." Thesis, Queen Mary, University of London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509603.
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Szeinbaum, Nadia Heliana. "Role of microbial manganese respiration in the anaerobic cycling of nitrogen." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53407.
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Despite the environmental significance of microbial manganese reduction, the molecular mechanism of microbial manganese respiration remains poorly understood. Soluble Mn(III) has been recently found to be a dominant soluble species in aquatic systems, yet little is known about the identity of microbial populations catalyzing Mn(III) reduction in the environment nor the molecular mechanism of Mn(III) respiration. In this research, a suite of Mn(III) reduction-deficient mutant strains were isolated, including Mn(III) reduction-deficient mutant strain Mn3-1 that also displayed the ability to reduce soluble organic-Fe(III), but not solid Fe(III) oxides, demonstrating for the first time that the reduction of soluble organic-Fe(III) and solid Fe(III) oxides proceed through electron transport pathways with at least one distinct component. This work also shows that the electron transport pathway for Mn(III) reduction in S. oneidensis shares many of the electron transport components of Fe(III) and Mn(IV) reduction pathways and that Mn(IV) reduction to Mn(II) proceeds step-wise through two one-electron transfer reactions with Mn(III) as a transient intermediate. Finally, sediment incubations were carried out to enrich for NH4+ oxidizing- Mn(III) reducing consortia. The Mn(III) reducing consortium was found to be dominated by an electrogenic Ochrobactrum sp. and a Shewanella sp. The isolated Shewanella strain is able to oxidize acetate with Mn(III) as electron acceptor, an activity never observed before in a metal-reducing member of the Shewanella genus.
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Naqasima-Sobey, Milika. "The role bottom sediments in nitrogen cycling in a tropical lagoon." Thesis, University of Essex, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402709.
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Kritzler, Ully H. "Biological and environmental drivers of carbon and nitrogen cycling in peatland." Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=192155.
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Peatlands are one of the largest global terrestrial carbon (C) pools, and play a vital role in provision of key ecosystem functions and as refugia for biodiversity. Many peatlands continue to be exploited with lowland raised bogs among the most affected by human modification. It is also now recognised that global climate change has potential to cause further impacts to peatlands, and it is thought that northern peatlands are particularly vulnerable to changes in temperature and precipitation. In this thesis, I report from a series of experiments to test; 1) the effect drought on soil CO2 efflux and photosynthate allocation, and production and chemical composition of dissolved organic carbon in leachate, 2) the effects of ericoid mycorrhizal (ERM) fungal necromass on soil CO2 efflux, 3) whether nitrogen (N) from ERM fungal necromass is important for plant nutrition, and 4) how different species of ERM fungi affect C and N turnover. These experiments were undertaken using a combination of field manipulations and measurements, and establishment of simplified mesocosms and microcosm systems. My results show that soil CO2 efflux in lowland degraded peatland is driven by the depth of water table, and that management of these systems from a C cycling perspective should consider ways to stabilise water table depth. Interpretation of data from field-girdling of C. vulgaris plants and 13CO2 pulse labelling strongly suggested that recent plant photosynthate has little apparent effect on this flux in contrast to many other ecosystems. Although the biomass of ERM fungi is often assumed to have a minor role in C cycling, my data show that the necromass of these fungi is highly labile and turnover rapidly, with potential to make important contributions to CO2 efflux and other microbially-driven processes.
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Heise, Julia [Verfasser], and Rainer [Akademischer Betreuer] Meckenstock. "Nitrogen cycling in technical water systems / Julia Heise ; Betreuer: Rainer Meckenstock." Duisburg, 2021. http://d-nb.info/1232175986/34.
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Wischer, Daniela. "Methylated amine-utilising bacteria and microbial nitrogen cycling in Movile Cave." Thesis, University of East Anglia, 2014. https://ueaeprints.uea.ac.uk/56877/.
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Movile Cave is an unusual, isolated ecosystem which harbours a complex population of microorganisms, fungi and endemic invertebrates. In the absence of light and with no fixed carbon entering the cave, life is sustained by non-phototrophic microorganisms such as sulfur and methane oxidisers. Also present are methylotrophs that use one-carbon compounds such as methanol and methylated amines as their sole source of carbon and energy. Produced during putrefaction, methylated amines are likely to be major degradation products in Movile Cave. Further to being methylotrophic substrates, they are also a nitrogen source for many non-methylotrophic bacteria. The role of methylated amines as carbon and nitrogen sources for Movile Cave bacteria was investigated using a combination of DNA stable isotope probing and cultivation studies. Both, well-characterised and novel methylotrophs were identified: Methylotenera mobilis dominated 13C-monomethylamine SIP enrichments, while members of Catellibacterium, Cupriavidus and Altererythrobacter were also active. Cultivation studies consolidated SIP results in obtaining the first methylotrophic isolates from the genera Catellibacterium and Mesorhizobium. Pathways for monomethylamine (MMA) metabolism were investigated using new PCR primers designed to target gmaS, the gene for gammaglutamylmethylamide synthetase, a key enzyme of the recently characterised indirect MMA oxidation pathway. This pathway is also present in bacteria that use MMA only as a nitrogen source, while the well-characterised, direct MMA oxidation pathway involving methylamine dehydrogenase (mauA) is found only in methylotrophs. gmaS was present in all MMAutilising isolates, while mauA was found only in some methylotrophs, suggesting the indirect pathway is the major mode of MMA oxidation both in methylotrophs and non-methylotrophs from Movile Cave. Preliminary gmaS surveys revealed a high diversity of gmaS-containing bacteria. The roles of N2 fixers and nitrifiers were also investigated. Both bacterial and archaeal ammonia oxidisers were found to be active; however, sulfur oxidisers appeared to be the dominant autotrophs in Movile Cave.
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Schoenholtz, Stephen H. "Restoration of nitrogen and carbon cycling in an Appalachian mine spoil." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/28437.
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Nitrogen deficiencies have long been acknowledged as a factor limiting the restoration of ecosystems destroyed by surface mining in the Appalachian Region of the U.S. The fundamental ecological structure and function common to intact terrestrial ecosystems are largely lacking in mine soils. Reliable guidelines for effective long-term restoration require a detailed understanding of the ecological processes occurring within the mine-soil system. The objective of this study was to determine the extent to which inorganic N fertilization, native topsoil replacement, or whole-tree wood-chip amendment affected the restoration and reforestation of an Appalachian mine-soil system through changes in C and ~ dynamics. Eighteen concrete tank lysimeters filled with mine spoils served as experimental microcosms to test hypotheses set forth in this study. Treatment effects on soil N and C pools, herbaceous biomass production, N uptake, N fluxes between pools, net leachate N losses, and early growth of pitch x loblolly hybrid pines were evaluated at regular intervals between July 1987 and October 1989. Inorganic N fertilization increased aboveground herbaceous biomass yield and N uptake by 87 and 71%, respectively, during the first growing season, but did not significantly affect yield or N uptake thereafter. During the first growing season, biomass production was 38% higher in the topsoil-amended mine soil than the unamended control. This resulted in an additional 17.4 kg N ha-1 sequestered in comparison to the control. Biomass yield was 270 and 19% lower in the wood-chip-amended mine soil than the unamended control after the first and third growing seasons, respectively. This resulted in 63 and 25% less N uptake, respectively, than the control. Survival of pitch x loblolly pine after two growing seasons was 90% in the N-fertilized mine soil and 71% with the fertilizer control treatment. This difference in survival was the result of lower water potential in the unamended mine soil during the growing season in which the trees were planted. Nitrogen fertilization did not significantly affect tree growth or nutrition. Pine survival after two growing seasons was 83, 98, and 60% for the unamended control, wood-chip, and topsoil treatments, respectively. By the end of the second growing season, the wood-chip treatment also resulted in greater tree height, ground-line diameter, and stem-volume index by 30, 49, and 203% respectively, when compared to the control. Increased survival and growth in the wood-chip-amended mine soil were directly related to higher soil water potential than the control or topsoil treatments. Total inorganic N leaching loss from N-fertilized mine soil was 47.64 kg ha-1 yr-1 higher than the control during the first growing season. However, N fertilization losses were not significantly higher during the remainder of the study period. Drainage was significantly higher during all three growing seasons in the wood-chip-amended mine soil. This resulted in lower N sequestering during the third growing season when precipitation was most abundant. Topsoil amendment did not significantly affect N leaching losses. Inorganic N fertilization did not significantly affect total organic C, total N, or N availability indices in the mine soil. Following topsoil addition, mine-soil total N was 294% higher than the unamended control. Wood-chip effects on the soil organic-matter pool were more gradual; however, by the end of the study, total N and total organic C were 18 and 95% higher, respectively in the wood-chip-amended mine soil than in the unamended control. Aerobic incubation of soil samples collected near the end of the second growing season showed that the topsoil and wood-chip amendments increased the N mineralization potential by 101 and 55%, respectively, in comparison to the unamended control. Furthermore, the mineralization rate constant of the wood-chip-amended mine soil was 44% lower than the control. This shows a slower rate of N turnover and more stable mine-soil N pool with the wood-chip treatment. This study shows that inorganic N fertilizer effects on N and C dynamics were rapid but transient. In contrast, the surface-applied amendments of native topsoil and whole-tree wood chips improved the potential for successful restoration of forests by increasing the N cycling capacity of the developing mine-soil system.Ph. D.
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Kim, Dong Yeob. "Municipal wastewater effects on nitrogen cycling in a mature hardwood forest." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/40072.
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Land disposal of municipal wastewater is considered ecologically acceptable and cost effective. The success of land treatment systems, however, requires proper functioning of all ecosystem components. The impact of municipal wastewater irrigation on the structure and function of an Appalachian hardwood forest in Virginia was investigated. Four irrigation rates (17.5, 35, 70, and 140 em yr⁻¹ ) were applied in this hardwood forest, and their effects on forest nutrient cycling were monitored for two years. Tree growth, seedling reproduction, tree mortality, species diversity, and N sequestering by vegetation were not changed significantly. Herbaceous ground cover increased due to irrigation, except for the 140 cm yr⁻¹ treatment where the heavy spray caused physical damage to the cover. Depending on the rate applied, the mature hardwood forest system sequestered only -3.4 to 8.2 kg N ha yr⁻¹ in the above ground biomass. Therefore, the fate of added N to the system became a function of N transformation processes in the soil. Nitrogen mineralization and nitrification increased as irrigation increased. Denitrification rates were not affected by irrigation; the process of denitrification did not constitute a significant N output from the forest system. The additional soil nitrate (N0₃) was left to leach because of the low assimilation by the plant/soil system and the low denitrification rate. Nitrogen storage decreased in the forest floor due to the increase in litter decomposition, and increased in the surface soil due to the increase in microbial N assimilation. Total soil N increased on the low irrigation sites and decreased on the high irrigation sites, indicating that high rates of irrigation stimulated N loss from the soil by enhancing soil N transformations. The health of the forest ecosystem was not adversely affected during this period, but the forest did not serve as a net sink for N. There was little opportunity for N sequestering in this mature hardwood forest. Without harvesting and regeneration, the system is likely to lose system N when wastewater is applied. When wastewater is applied to lands, N sequestering and denitrification should be maximized in order to minimize the pollution potential of N0₃ leaching to groundwater systems.Ph. D.
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Bamber, Kevin William. "Nitrogen Cycling from Fall Applications of Biosolids to Winter Small Grains." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/71870.
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Environmental concerns about winter nitrogen (N) leaching loss limit the amount of biosolids applied to winter small grains in Virginia. Ten field studies were established 2012-2014 in Virginia to determine the agronomic and environmental feasibility of fall biosolids applications to soft red winter wheat (Triticum aestivum L.). Eight studies were located in the Coastal Plain physiographic province and two in the Ridge and Valley physiographic province. The effects of eight biosolids and urea N treatments on 1) biomass production at Zadoks growth stage (GS) 25-30, 2) soil inorganic N at GS 25-30, 3) soil mineralizable N at GS 25-30,4) N use efficiency (NUE) at GS 58, 5) grain yield, 6) end-of-season soil inorganic N, and 7) estimated N recovery were studied. Anaerobically digested (AD) and lime stabilized (LS) biosolids were fall applied at estimated plant available N (PAN) rates of 100 kg N ha-1 and 50 kg N ha-1. The 50 kg N ha-1 biosolids treatments were supplemented with 50 kg N ha-1 as urea in spring. Urea N was split applied at 0, 50, 100 and 150 kg N ha-1, with 1/3 applied in fall and 2/3 in spring. Biomass at GS 25-30 increased with urea N rate and biosolids always resulted in equal or greater biomass than urea. Soil mineralizable N at GS 25-30 rarely responded to fall urea or biosolids N rate, regardless of biosolids type. Biosolids and urea applied at the agronomic N rate resulted in equal grain yield and estimated N recovery in soils where N leaching loss risk was low, regardless of biosolids type or application strategy. Lime stabilized biosolids and biosolids/urea split N application increased grain yield and estimated N recovery in soils with high or moderate N leaching loss risk. Therefore, AD and LS biosolids can be fall-applied to winter wheat at the full
agronomic N rate in soils with low N leaching loss risk, while LS biosolids could be applied to winter wheat at the full agronomic N rate in soils with moderate or high N leaching loss risk.Master of Science
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McCallum, Roisin. "Organic matter and nitrogen cycling in a heavily modified coastal lagoon." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2022. https://ro.ecu.edu.au/theses/2552.
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Coastal waterbodies and their catchments have been highly modified, leading to altered flushing and eutrophication. Strategies to manage water flow to either maintain water levels or reduce salt-water intrusion and mitigate impacts to coastal waterbodies include engineering approaches such as the construction of surge barriers and river diversions and manipulation of sandbars. Climate change is increasingly impacting coastal waterbodies with predictions of increased drying and significant changes to rainfall patterns. Consequently, engineering management strategies are likely to increase, but it is unclear how biogeochemistry and benthic cycling in coastal waterbodies will be affected, and how to manage the likely eutrophication issues that ensue. Therefore, the aim of this project was to determine how organic matter and nutrients are transported and cycled within a heavily modified intermittently closed/open lakes and lagoons (ICOLL). The Vasse Wonnerup Wetland System (VWWS) is a modified eutrophic ICOLL in southwestern Australia. It has been managed for over 100 years and has multiple surge barriers, river diversions, an oxygenation plant, and an artificially managed sandbar. In addition, significant portions of the VWWS seasonally dry out, making it an ideal system to study the effects of climate change to coastal systems which are likely to experience similar modifications as the VWWS. Stable isotope analyses and mixing models showed that the particulate organic matter (POM) in the system is derived mainly from autochthonous sources (fringing vegetation and aquatic macrophytes). Similarly, compound-specific stable isotopes showed that the sources of dissolved organic matter (DOM) are mainly autochthonous and dominated by dissolved organic nitrogen (DON). The extremely low ( < detection limit) concentrations of dissolved inorganic nitrogen (DIN; nitrate and ammonium) in the basin water column suggests that DON is crucial to sustaining a DIN supply in the VWWS through decomposition and tight cycling between DON and DIN. Currently, national and international management guidelines focus on inorganic nutrient concentrations as indicators of unacceptable concentrations (trigger values) and management strategies are generally focused upon reducing allochthonous (external) dissolved inorganic nutrients (i.e., nitrate, ammonium, and phosphate). This study shows that the focus of management on inorganic nutrients may not be well placed in this type of system. Benthic flux experiments demonstrated that water column DO and seasonal drying of the sediment did not affect dissolved organic C, N or P fluxes significantly but did influence benthic metabolism with higher rates occurring in high water column DO conditions. Despite this, benthic metabolism remained anaerobic. Surprisingly, decreasing water column DO did not influence net greenhouse gas (GHG) emissions indicating increasing water column DO will not decrease GHG emissions. Oxygenation of the water column did increase N removal, with higher net N2 effluxes with increasing water column DO. Bioavailable nitrogen pools the water column were supplemented in low DO conditions by N2O, with consumption of N2O occurring during dark hours. The lack of significant effects from DO manipulation treatments on many of the measured nutrient species indicate that maintenance of water column oxic conditions, regardless of the concentrations are unlikely to be effective in promoting removal or storage of nutrients in eutrophic systems. Increasing drying out of coastal waterbodies will have impacts on benthic metabolism, however this issue may become system specific depending on sandbar and surge barrier management strategies influencing water levels. Overall, this study confirmed the importance of autochthonous OM contributions and cycling in an ICOLL, whilst highlighting the impacts of engineered modifications in this type of coastal waterbody and its catchment.
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Liang, Baochang. "A study of corn production and nitrogen cycling in the soil-plant system." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39426.
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Increased N fertilizer efficiency in crop production is essential for agronomic, economic, and environmental improvement. In order to increase efficiency, a basic knowledge of fertilizer-soil-crop relationships and components is required. Nitrogen components in the soil-corn system were determined on two soils (Chicot sandy clay loam, Grey Brown Luvisol; Ste. Rosalie clay, Humic Gleysol). Fall soil NO$ sb3 sp-$-N levels increased linearly with increasing N rates above the 170 kg ha$ sp{-1}$ N rate. Changes in soil NO$ sb3 sp-$-N over winter were a function of both fall soil NO$ sb3 sp-$-N levels and winter precipitation. Denitrification rates during the non-growing season ranged from 7 to 24 kg N ha$ sp{-1}$, mainly dependent on N fertilizer rates the previous growing season on the Ste. Rosalie soil. Denitrification losses were a small portion of NO$ sb3 sp-$ disappearance over the non-growing season. Almost all fertilizer N at 170 kg N ha$ sp{-1}$ was recovered as crop N, clay fixed NH$ sb4 sp+$ and organic immobilized N at the end of the growing season, where at 400 kg ha$ sp{-1}$ N fall mineral N and unaccounted for N were a major component of the N fractions. High rates (400 kg N ha$ sp{-1}$) compared to normal rates (170 kg N ha$ sp{-1}$) resulted in some increase in yield, greater microbial activity and greater soil organic N, and a significant loss of fertilizer N by denitrification or leaching.
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Walecka-Hutchison, Claudia Walworth James L. "Nitrogen dynamics in diesel biodegradation effects of water potential, soil C:N ratios, and nitrogen cycling on biodegradation efficacy /." FIND on the Web, 2005.
Find full textAbstract:
Thesis (Ph. D. - Soil, Water, and Environmental Science)--University of Arizona.Appendix A - Hydrocarbon biodegradation rates and water potential in nitrogen augmented desert soils, by Claudia Walecka-Hutchison and James L. Walworth ; Appendix B - Assessment of C:N ratios and water potential for nitrogen optimization in diesel bioremediation, by Claudia Walecka-Hutchison and James L. Walworth ; Appendix C - Evaluating the effects of gross nitrogen mineralization, immobilization and nitrification on nitrogen fertilizer availability during diesel biodegradation, by Claudia Walecka-Hutchison and James L. Walworth. Includes bibliographical references (leaves 71-82) and appendices.
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Walecka-Hutchison, Claudia. "Nitrogen dynamics in diesel biodegradation : effects of water potential, soil C:N ratios, and nitrogen cycling on biodegradation efficacy." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/191274.
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Respirometric experiments were performed to evaluate the role of nitrogen in aerobic diesel biodegradation. Specific objectives included 1) evaluating the effects of water potential induced by various nitrogen amendments on diesel biodegradation rates in arid region soils, 2) comparing concurrent effects of C:N ratios and soil water potential on diesel degradation rates, and 3), measuring gross rates of nitrogen cycling processes in diesel-contaminated soil to determine duration of fertilizer bioavailability. In all studies, increasing nitrogen fertilization resulted in a decrease in total water potential and correlated with an increase in lag phase and overall reduction in microbial respiration. Highest respiration and estimated diesel degradation was observed in the 250 mg N/kg soil treatments regardless of diesel concentration, nitrogen source, or soil used, suggesting an inhibitory osmotic effect from higher rates of nitrogen application. The depression of water potential resulting in a 50% reduction in respiration was much greater than that observed in humid region soil, suggesting higher salt tolerance by microbial populations of arid region soils. Due to the dependence on contaminant concentrations, use of C:N ratios was problematic in optimizing nitrogen augmentation, leading to over-fertilization in highly contaminated soils. Optimal C:N levels among those tested were 17:1, 34:1, and 68:1 for 5,000, 10,000 and 20,000 mg/kg diesel treatments respectively. Determining nitrogen augmentation on the basis of soil pore water nitrogen (mg N/kg soil H₂0) is independent of hydrocarbon concentration but takes into account soil moisture content. In the soil studied, optimal nitrogen fertilization was observed at an average soil pore water nitrogen level of 1950 mg N/kg H₂0 at all levels of diesel contamination. Based on the nitrogen transformation rates estimated, the duration of fertilizer contribution to the inorganic nitrogen pool at 5,000 mg/kg diesel was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg/kg nitrogen treatments respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were assumed as losses of fertilizer with only gross mineralization of native organic nitrogen contributing to the most active portion of the nitrogen pool.
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Webster, Alison Mary. "An investigation of the microbial ecology of biofilms from a model gravel bed hydroponic system." Thesis, University of Portsmouth, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327015.
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Campbell, Graeme Roy. "Community analysis of β-subgroup ammonia in sewage sludge amended soil." Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602053.
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European legislation has increased pressure on the use of land to represent the major disposal option for sewage sludge. Owing to their importance in regulating soil fertility, much research has been conducted into the effects of sewage sludge application on soil microorganisms. However, little knowledge is known about its effects on community dynamics of the beta-subgroup ammonia oxidising bacteria. This is despite the fact that nitrification activity of these bacteria plays an important role in soil nitrogen cycling. This investigation aimed to examine community dynamics of the beta-subgroup ammonia oxidising bacteria in sewage sludge amended soil by employing recently developed molecular based techniques. Firstly, a soil DNA extraction protocol was identified that allowed routine nested PCR amplification of 16S rDNA using beta-subgroup ammonia oxidiser directed primers. Reproducibility observed in denaturant gradient gel electrophoresis (DGGE) profiles suggested that 0.5 g samples used for DNA extraction allowed consistent detection of dominant beta-subgroup ammonia oxidiser community members. The effects of applying primary treatment sewage sludge to a variety of contrasting soils on (3-subgroup ammonia oxidiser community structure was unclear. This was partially hampered by lack of specificity of PCR primers for non ammonia oxidiser 16S rDNA sequences. Further, through measurement of net nitrification, there was no indication that sewage sludge addition stimulated the activity of nitrifier populations. Nevertheless, this study indicated the usefulness of DGGE for screening multiple environmental samples. A set of hierarchical oligonucleotide probes exhibiting specificity at the group, genus and cluster level were optimised using a non-radioactive system. These probes were used to assess the effects of application of aerobically digested sewage sludge to soil for 4 y on beta-subgroup ammonia oxidiser community structure. Despite significant changes in measurable soil parameters including net nitrification activity no changes were observed in beta-subgroup ammonia oxidiser community structure. This indicated resilience of these communities to change. A final study was conducted examining the effects of application of anaerobically digested sewage sludge to soil on beta-subgroup ammonia oxidiser community structure. Inhibition of nitrification by acetylene indicated the presence of a viable population of ammonia oxidising bacteria in continuously shaken samples of sludge. DGGE and oligonucleotide probing analysis provided evidence that sewage populations had the potential to outcompete indigenous soil populations of beta-subgroup ammonia oxidising bacteria. This was despite the fact that MPN enumeration suggested that soil populations of these bacteria were in some cases 10-fold greater than sludge populations. Evidence was also provided that suggested net nitrification to be an unreliable indicator of ammonia oxidiser activity in soil. It is possible to conclude that community structure of the beta-subgroup ammonia oxidising bacteria may be altered by application of sewage sludge to soil. The effects on community structure are likely to be influenced by both the type and level of sludge applied to soil.
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Hall, Jennifer M. "Manipulation of N mineralisation/immobilisation dynamics to investigate poor fertiliser recovery in improved grass pasture on ombrotrophic peat." Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU068793.
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The spring application of fertiliser N often fails to stimulate grass growth in improved grass pastures on peaty soils. Fertiliser utilisation efficiencies under these conditions have been found to be low, suggesting that available N is not taken up by the plant. Previous work has suggested that in this type of system, the soil microbial biomass may function as a strong sink for fertiliser N and therefore limit plant growth in the Spring. A series of laboratory based experiments utilising reconstituted and intact cores, and homogenised peat, was set up to identify the factors controlling the competition between N uptake by plants and N immobilisation by soil microorganisms following the addition of fertiliser N to peat. Microbial biomass N concentrations were determined in order to quantify the amount of N present in the microbial pool. The use of 15N labelled fertilisers and selective biocides provides a powerful tool with which to characterise the microbial population responsible for the immobilisation of N under these conditions. Improvement of a grass pasture at Sletill Hill has resulted in the formation of a distinct layer comprised of partially decomposed roots, underneath the surface vegetation and it was within this layer, that microbial immobilisation of fertiliser N was found to occur. Approximately 30% of applied N (equivalent to ca 50 kgN ha-1) was found within the microbial biomass in this layer, 30 days after the addition of fertiliser N. Intact cores were removed from Sletill Hill and maintained under controlled abiotic conditions. Water table level and temperature were found to be important in controlling the extent of microbial immobilisation of applied N. Lowering the water table level increased the quantity of N present in plant and microbial N pools, particularly at lower temperatures (8°C). At higher temperatures (20°C), plant uptake of N tended to be less due to a restriction on plant growth caused by 'droughty' soil conditions.
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Mitchell, Mark E. "Nutrient Cycling Dynamics and Succession in Green Roof Ecosystems." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin150487303109878.
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