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1
Rhodes, Phillip Steven. "The interaction between maternal nutrient restriction and postnatal nutrient excess in an ovine model." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12092/.
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Evidence from human and animal studies has highlighted the sensitivity of the developing fetus to environmental insults, such as maternal undernutrition, during gestation. These nutritional perturbations to the intrauterine milieu may engender a legacy of deleterious health consequences in adulthood. This thesis presents a series of studies which test the `mis-match‘ fetal programming theory; that is, whether a nutritionally poor diet prenatally interacts with a nutritionally excessive diet postnatally to overtly increase risk factors for adult disease. The effect of a maternal global energy restriction is contrasted against a maternal specific protein restriction, each fed during either early or late gestation. Adult offspring were subsequently exposed to an obesogenic environment (elevated feed with increased lipid content whilst restricting physical activity). Offspring metabolic flexibility and competence were assessed through routine blood samples throughout postnatal life and at 7, 18 and 24 months of age by glucose (GTT) and insulin (ITT) tolerance tests and body composition by dual energy x-ray absorptiometry. In general males appeared more susceptible to developmental programming than females at a number of timepoints. Furthermore, an increased first-phase or incremental area-under-the-insulin-response curve was observed in 1) offspring following maternal protein restriction in early gestation at 7 and 24 months of age, despite maternal protein restriction in late gestation significantly reducing birthweight and 2) in offspring exposed to maternal energy restriction during late gestation at 24 months of age in response to a GTT. Since, in both groups, the response of all offspring to an ITT (from a euglycemic baseline) was similar, infers that developmental programming in sheep followed by nutritional excess is first revealed as affecting either the pancreas (~insulin hypersecretion) or the liver (hepatic insulin resistance, reduced first-pass insulin metabolism). The studies illustrate the importance of habitual consumption of an `optimal’ balanced diet through gestation on postnatal health, especially in light of the current obesity epidemic.
2
Chapman, K. "Interaction between tree species : Decomposition and nutrient release from litters." Thesis, Lancaster University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234635.
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Hamzah, Norhayati. "A bifurcation analysis of a multi compartment plankton-zooplankton-nutrient interaction." Thesis, University of Canterbury. Mathematics and Statistics, 2004. http://hdl.handle.net/10092/5702.
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This thesis concentrates on understanding the long term behaviour of a multi-compartment phytoplankton-zooplankton-nutrient interaction. A variable-yield model is considered, in which the rate of carbon uptake by phytoplankton necessary for its growth is governed by cell quota i.e. the ratio of external nutrient (nitrogen) and the internal nutrient (carbon). The internal and external nutrient of the phytoplankton are governed by separate equations. The work addresses the question 'How complex should a model be?', besides attempting to understand analytical and qualitative model behaviour. The simplest model considered consists of four ordinary differential equations relating to one pool or compartment, and is then extended to eight ordinary differential equations: (four equations for each pool) of the two compartments, and finally to twelve ordinary differential equations: (four equations in each of the three compartments).
Chapter 1 introduces the basic mathematical model, and critiques its formulation based on various ecological studies on phytoplankton-zooplankton-nutrient interactions. Local stability analysis necessary to investigate stability of our model is discussed, together with an introductory explanation of bifurcation theory, which is used by modellers to tune and adjust the dynamical system. Thus by altering system parameters the behaviour of the system may change gradually or even abruptly. Abrupt changes occur at bifurcating values of the parameter. Chapter 1 also includes a manual for running the software XPP and also AUTO, sophisticated software to study bifurcation and hence important model behaviour.
Chapter 2 provides a complete analysis of the behaviour of the one compartment model. It includes local stability analysis for all the solutions and a global analysis for the null solution. A detailed study of this simplest model includes a complete profile of bifurcation diagrams executed by the software AUTO, with information on the behaviour of the steady state and periodic solutions for comparison with an extension of the analytical results.
Chapter 3 presents analytical as well as numerical studies of the two compartment model. Two cases are considered, one with an equal growth parameter of the phytoplankton and the other where the growth parameter in each compartment is different. Stability analysis for the first case is examined by both local stability analysis and bifurcation analysis, but other case can only be done numerically via a complete profile of bifurcation diagrams using the software AUTO.
Chapter 4 presents stability analysis for the three compartment model via bifurcation diagrams generated numerically using AUTO. This chapter considers 3 cases: the equal growth parameter of phytoplankton, different growth parameters of phytoplankton and both different growth parameters and different diffusion parameters.
Chapter 5 presents the various conclusions drawn from all of three models considered.
4
Fotopoulos, Vasileios. "Molecular analysis of nutrient transfer in the host/powdery mildew interaction." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398738.
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Wan, Hon Chi Judy. "Interaction of earthworms and microorganisms on nutrient availability and crop growth." HKBU Institutional Repository, 2004. http://repository.hkbu.edu.hk/etd_ra/588.
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Millar, Kristina K. "Antibiotic Efficacy and Interaction in Escherichia coli during Varying Nutrient Conditions." Scholarship @ Claremont, 2016. http://scholarship.claremont.edu/scripps_theses/809.
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Due to the recent rise in antibiotic resistant pathogens, and the difficulties surrounding the quest for new antibiotics, many researchers have started revisiting antibiotic interactions in hopes of finding new treatment options. The primary outcome of this project was to examine the efficacy of concomitant antibiotic use under varying nutrient conditions, to identify variations in antibiotic interactions. Antibiotic interactions were studied, utilizing E. coli as a model bacterial system, grown in four different media types. E. coli cultures were treated with streptomycin, tobramycin, erythromycin, and amikacin individually and in a pairwise fashion at varying doses. We found that at least some antibiotic efficacies were dependent on the environmental nutrient conditions E. coli was grown in, as the antibiotics were not equally effective in all media types. E. coli grown in potato dextrose broth, in particular, showed extremely high tolerance to antibiotic inhibition. In addition, we observed several variations in antibiotic interactions, depending on the combination of antibiotics and environmental conditions utilized. It is predicted that differences in available nutrients is the primary cause of the observed discrepancies in antibiotic properties between media. The observation of changes in antibiotic efficacy under different environmental and nutrient conditions has serious implications for use of antibiotic combinations as drug treatments. Not all microenvironments within the human body have identical nutrient make-up. If the interactions antibiotics are reported to have in one environmental condition change under another, reckless prescription of combinations could lead to a serious adverse reaction. Thus, this is an important area for future in vitro and in vivo research.
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Wilson, Carol Patricia. "The MTHFR C677T polymorphism and riboflavin : a novel gene-nutrient interaction affecting blood pressure." Thesis, University of Ulster, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.554915.
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Hypertension IS a major risk factor for CVD and unequivocal evidence has demonstrated a continuous and linear relationship between elevated blood pressure (BP) and stroke. Among the many established risk factors for hypertension, a novel gene- nutrient interaction with a potential role in BP has recently emerged. A common polymorphism (677C---)oT) in the gene encoding the folate-metabolising enzyme methylenetetrahydrofolate reductase (MTHFR) produces a variant enzyme with decreased activity, and recent work at this centre in premature CVD patients reported that stabilisation of the variant enzyme by administration of its cofactor riboflavin may lower BP. The aim of this thesis was to further investigate the association between the MTHFR 677C---)o T polymorphism and BP and to evaluate the potential modulating role of riboflavin. The findings of this thesis demonstrated that riboflavin supplementation at the dietary level (1.6mg/dI16weeks) produced a genotype-specific lowering of BP that was clinically significant and that this effect was not confined solely to high-risk CVD patients but may in fact be applicable to hypertensive patients generally with the TT genotype. Preliminary work using 24-hour ambulatory blood pressure monitoring (ABPM) reported a non-significant trend towards higher BP in those with the TT genotype compared to those with the CC and CT genotypes. It also appeared to suggest that MTHFR genotype may have an effect on nocturnal BP characterised by non- dipping status, itself a cardiovascular risk factor independently of 24-hour blood pressure. In conclusion this thesis has confirmed that the MTHFR 677 TT genotype is a risk factor for hypertension and that optimisation of riboflavin status offers a targeted nutritional therapy with clinically relevant effects on BP specifically in this genotype group. Given the frequency of this polymorphism worldwide and the global burden of blood pressure-related disease, these findings could have important public health implications.
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Fernández, Del-Saz Néstor. "In vivo metabolic regulation of plant respiration under salt and nutrient stress. Interaction with mycorrhyza." Doctoral thesis, Universitat de les Illes Balears, 2017. http://hdl.handle.net/10803/462999.
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- Introducció
El paper fisiològic i regulació de la oxidasa alternativa (AOX) en plantes sota estressos
nutricionals y salins no estan del tot resolts. Ambdós estressos indueixen canvis metabòlics
relacionats amb el metabolisme del carboni, estat redox i demanda energètica que poden
portar a canvis en l’activitat in vivo de la AOX per conferir tolerància a l’estrès. Mes
investigació es necessària para desxifrar el paper de la respiració alternativa conferint
flexibilitat metabòlica. Por exemple, l’ús de la simbiosi amb micorrizes arbusculars (AM)
reputades per incrementar en plantes la nutrició y tolerància a estrès abiòtic ens permet
hipotetitzar que la activitat in vivo de la AOX està regulada per canvis metabòlics i nutricionals.
- Contingut de la investigació
Aquesta Tesi està basada en la idea que l’ús de micorrizes aportarà informació important
sobre la regulació de la activitat de la AOX sota condicions de salinitat i limitació de fòsfor en el
sòl. Jo hipotetitzo que (1) L’activitat AOX confereix tolerància a les plantes sota condiciones de
salinitat; (2) L’ activitat AOX confereix flexibilitat metabòlica sota condiciones de salinitat; (3)
L’activitat AOX contribueix a incrementar el creixement en plantes micorrizades sota
condiciones de dèficit de fòsfor i salinitat; (4) L’ activitat AOX contribueix a disminuir la
respiració en arrels de plantes micorrizades degut a la reducció en la síntesis de carboxilats
rizosfèrics; i (5) L’activitat AOX està regulada per canvis en la concentració de fòsfor en plantes.
- Conclusió
1) L’activitat AOX permet la síntesi d’aminoàcids i àcids orgànics amb un paper protector en
una col·lecció de genotips de Medicago truncatula sota un curt i sever estrès salí.
2) L’activitat AOX permet la continuïtat de las reaccions del cicle dels àcids tricarboxílics sota
un curt i sever estrès osmòtic en Arabidopsis thaliana.
3) L’activitat AOX contribueix a incrementar el creixement de la part aèria en plantes de
Nicotiana tabacum colonitzades amb Rhizophagus intraradices sota una prolongada limitació
de fòsfor i exposició a salinitat.
4) L’activitat AOX contribueix a disminuir la respiració radicular en plantes de Nicotiana
tabacum degut a la seva reduïda síntesi de carboxilats rizosfèrics.
5) La activitat AOX està regulada por canvis en la concentració de fòsfor en plantes de
Solanum lycopersicum.
Per tant, l’uso de micorrizes ha aportat important informació sobre la regulació de la activitat
AOX sota diferents escenaris de concentracions variables de sal i disponibilitat de fòsfor en
sòls, demostrant ser dependent de canvis nutricionals i metabòlics, como va ser originalment
hipotetizat.- Introducción El papel fisiológico y regulación de la oxidasa alternativa (AOX) en plantas bajo estreses nutricionales y salinos no es del todo comprendida. Ambos estreses inducen cambios metabólicos relacionados con el metabolismo del carbono, estado redox y demanda energética que pueden llevar a cambios en la actividad in vivo de AOX para conferir tolerancia a estrés. Más investigación es necesaria para descifrar el papel de la respiración alternativa confiriendo flexibilidad metabólica. Por ejemplo, el uso de la simbiosis con micorrizas arbusculares (AM) reputadas por incrementar en plantas la nutrición y tolerancia a estrés abiótico nos permite hipotetizar que la actividad in vivo de AOX está regulada por cambios metabólicos y nutricionales. - Contenido de la investigación Esta Tesis está basada en la idea de que el uso de micorrizas aportará importante información sobre la regulación de la actividad de AOX bajo salinidad y limitación de fósforo en suelo. Yo hipotetizo que (1) La actividad AOX confiere tolerancia en plantas bajo salinidad; (2) La actividad AOX confiere flexibilidad metabólica bajo salinidad; (3) La actividad AOX contribuye a incrementar el crecimiento en plantas micorrizadas bajo déficit de fósforo y salinidad; (4) La actividad AOX contribuye a disminuir la respiración en raíces de plantas colonizadas debido a la reducida síntesis de carboxilatos rizosféricos; and (5) La actividad AOX está regulada por cambios en la concentración de fósforo en plantas. -Conclusiones 1) La actividad AOX permite la síntesis de protectores aminoácidos y ácidos orgánicos en una colección de genotipos de Medicago truncatula bajo severo y corto estrés salino. 2) La actividad AOX permite la continuidad de las reacciones del ciclo de los ácidos tricarboxílicos bajo severo y corto estrés osmótico en Abidopsis thaliana. 3) La actividad AOX contribuye a incrementar el crecimiento de la parte aérea en plantas de Nicotiana tabacum colonizadas con Rhizophagus intraradices bajo prolongada limitación de fósforo y exposición a salinidad. 4) La actividad AOX contribuye a disminuir la respiración radicular en plantas de Nicotiana tabacum debido a la reducida síntesis de carboxilatos rizosféricos. 5) La actividad AOX está regulada por cambios en la concentración de fósforo en plantas de Solanum lycopersicum. Por lo tanto, el uso de micorrizas ha aportado importante información sobre la regulación de la actividad AOX bajo diferentes escenarios de concentraciones variables de sal y disponibilidad de fósforo en suelos, demostrando ser dependiente de cambios nutricionales y metabólicos, como fue originalmente hipotetizado.
- Introduction Physiological role and regulation of alternative oxidase (AOX) in plants under both nutrient and salt stresses is still not well understood. Both stresses induce metabolic changes related to carbon metabolism, redox state and energy demand that may induce changes on the activity in vivo of AOX in order to provide tolerance to stress. Further research is needed to decipher the role of alternative respiration confering metabolic flexibility. For instance, the use of symbiosis with arbuscular mycorrhiza (AM), reputed by increase plant nutrition and tolerance to abiotic stresses, allows us to hypothesize that AOX activity in vivo is regulated by nutritional and metabolic changes. In addition, the effect of AM colonization on plant respiration is a controversial issue in literature. - About this Thesis The present Thesis is based on the idea that the use of mycorrhiza will provide important information about the regulation of AOX activity under salinity and P limitation. I hypothesized that: (1) AOX activity confers tolerance in plants under salinity; (2) AOX activity confers metabolic flexibility under salt stress; (3) AOX activity contributes to increase growth in AM colonized plants under phosphorus (P) limitation and salinity; (4) AOX activity contributes to decrease respiration in AM colonized roots due to the reduced synthesis of rhizosphere carboxylates; and (5) AOX activity is regulated by changes on plant P concentration. Results are presented in a form of 5 manuscript. Each resarch chapter includes one manuscript, submitted or already published. Introduction and Material and methods section are also presented in the form of submitted manuscripts. -Conclusions 1) AOX activity allows the synthesis of protectives aminoacids and organic acids in a particular collection of Medicago truncatula genotypes under sudden severe salt stress. 2) AOX activity allows the continuity of TCA cycle under sudden severe osmotic stress in Arabidopsis thaliana. 3) AOX activity contributes to increase shoot growth in Nicotiana tabacum colonized with Rhizophagus intraradices under long-term P limitation and salinity. 4) AOX activity contributes to decrease respiration in AM colonized roots of Nicotiana tabacum due to the reduced synthesis of rhizosphere carboxylates. 5) AOX activity is regulated by changes on P concentration in Non-AM and AM colonized plants of Solanum lycopersicum grown at different P availability in soil. Therefore, the use of mycorrhiza has provided important information about the regulation of AOX activity under different scenarios of changing concentrations of salt and P availability in soils, which was dependent on metabolic and nutritional status, as originally hypothesized.
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Sonawala, Unnati Subhash. "Understanding the role of host amino acid transporters in nutrient acquisition by oomycete pathogens." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/102868.
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Hyaloperonospora arabidopsidis (Hpa) is a naturally occurring oomycete pathogen on
Arabidopsis thaliana. It is related to downy mildews of economically important crops such as
cabbage, kale and broccoli, belonging to the Brassicaceae family. Downy mildew pathogens are
obligate biotrophs that extract nutrients exclusively from living plant cells. As a part of its obligate
biotrophy lifestyle, Hpa has lost the ability to assimilate inorganic nitrogen and sulfur. It thus has
to acquire these nutrients from the host in an organic form; possibly amino acids. Using a reverse
genetic approach, I was able to identify two host amino acid transporters that are up-regulated
during Hpa infection: AAP3 and AAP6. Both of these transporters are localized in the vasculature
of the plant, AAP3 mostly in the root, and AAP6 in the roots and shoots. Using transgenic lines of
Arabidopsis containing transcriptional and translational reporter fusion constructs for these genes,
I found that AAP3 displays increased mRNA accumulation which is attributable to an increased
promoter activity in regions of shoot tissue colonized by Hpa. On the other hand, AAP6 displays
a mild increase in mRNA accumulation under Hpa infection, but the induction becomes more
prominent at the protein level as seen by fluorescence from GFP fused to AAP6. Surprisingly,
null mutants of AAP3 did not impact Hpa growth whereas null mutants of AAP6 made the plant
more susceptible to Hpa. Furthermore, aap6 mutants accumulate fewer free amino acids in the
phloem compared to wild-type plants when infected with Hpa. Together, these results suggest that
AAP6 acts a nutritional starvation gene for the pathogen and hence aids the plant during infection.
While we now know more about AAP3's regulation during infection, its function remains to be
elucidated. To successfully colonize a plant, a pathogen must be able to achieve both suppression
of plant immunity and acquisition of nutrients from the plant host. While the former has been
well studied, research on the latter is sparse. This work was a step in the direction to increase our
understanding of potential players in nutrient acquisition by pathogens.Doctor of Philosophy
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Holderness, M. "Interaction of host stress and pathogen ecology on Phytophthora infection and symptom expression in nutrient film-grown tomatoes." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370136.
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Kavvadias, Victor. "Effect of calcium manganese interaction on the growth and nutrient uptake in Scots pine and black pine seedlings." Thesis, University of Aberdeen, 1996. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU079042.
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Acid soil infertility has been associated with excess of Al, either Mn toxicity or deficiency, deficiencies or toxicities of one or more other trace elements, or deficiencies of certain major nutrients such as Ca, Mg, P and K. Studies on the influences of these factors on the tree growth are useful in identifying the mechanisms and the genetic sources of tolerance to acid soil. A series of five culture experiments, under controlled conditions, were carried out using Greek and British Scots (Pinus sylvestris L.) seedlings as well as black pine seedlings of Greek (Pinus nigra Arnold var. nigricans Host) and 'British' (Pinus nigra var. maritima (Ait.) Melville) origin. Nine major and trace elements (N, P, K, Ca, Mg, Fe, Mn, Zn and Cu) were determined in the growth components of pine seedlings. The Mn and Ca requirements of the pine seedlings of all growth components were assessed. Foliar values found for the Mn (ppm) and Ca (%) concentrations associated with 90% of maximum yield were: a) Greek-derived Scots pine: Mn 84-855 and Ca 0.34-1.00, b) British-derived Scots pine: Mn 77-1,450 and Ca 0.43-0.87, c) Austrian pine: Mn *-2,100 and Ca 0.27-*, and d) Corsican pine: Mn *-1,400 and Ca 0.30-0.73 (* denotes not estimated). The results suggested that under conditions of low Ca availability, excessive Mn uptake could result in toxicity in Greek pines and the feed solution Ca/Mn concentration ratio is an important factor in determining the ability of British pines to tolerate adverse Mn conditions. The relative tolerance of Corsican pine to Mn toxicity is related both to immobilisation of Mn in roots by increased Ca uptake, particularly at low solution Ca availability, and to inhibition of Mn translocation from roots to the foliage, while that of British P.sylvestris is associated to its ability to withstand high Mn concentration in shoots. The characteristic nutritional behaviour of Corsican pine (exclusion of some essential elements from the foliage) appeared to be partly responsible for the induced Mg and Fe deficiencies by excess Mn availability. Furthermore, the adverse influence of increasing solution Mn availability on Ca concentration of pine seedlings is dependent on the availability of Ca in the nutrient solution, on the component part analysed, on the genotype and on the experimental conditions. The presence of two absorption mechanisms for Mn and a close functional relationship between Ca and Mn in foliage of seedlings is suggested.
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Walker, Beau Jensen. "The Interaction of Aeolian and Fluvial Processes in Dry Washes on the Colorado Plateau, USA." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5597.
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In the past decade there has been a call for integrated studies that examine the interaction of fluvial and aeolian processes (Belnap et al., 2011; Bullard and Livingstone, 2002). In this study, we examined the role of land-use, weather, and soil type on the flux of aeolian material into dry washes on the Colorado Plateau in central Utah, USA, and western Colorado, USA. Our goal was to quantify the impact of individual deposition and erosion events by correlating weather and land-use data with a combination of measurement methods including dust collection via dust traps, GPS surveying, and close-range photogrammetry. Our data suggest that there is an interaction between these processes and that seasonality and land-use play a large role in determining the strength of this interaction. Particularly, high land-use and dry, windy conditions were most conducive to the surface movement of sediment and subsequent removal of that sediment by fluvial processes.
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Choksi, Nidhi Rajan. "Characterizing Interaction Between PASK and PBP1/ ATXN2 to Regulate Cell Growth and Proliferation." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6527.
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Pbp1 is a component of glucose deprivation induced stress granules and is involved in P-body-dependent granule assembly. We have recently shown that Pbp1 plays an important role in the interplay between three sensory protein kinases in yeast: AMP-regulated kinase (Snf1 in yeast), PAS kinase 1 (Psk1 in yeast), and the target of rapamycin complex 1 (TORC1), to regulate glucose allocation during nutrient depletion. This signaling cascade occurs through the SNF1-dependent phosphorylation and activation of Psk1, which phosphorylates and activates poly(A)- binding protein binding protein 1 (Pbp1), which then inhibits TORC1 through sequestration at stress granules. In this study we further characterized the regulation of Pbp1 by PAS kinase through the characterization of the role of the Psk1 homolog (Psk2) in Pbp1 regulation, and the identification of functional Pbp1 binding partners. Human ataxin-2 (ATXN2) is the homolog of yeast Pbp1 and has been shown to play an important role in the development of several ataxias. In this study we have also provided the evidence that human ataxin-2 can complement Pbp1 in yeast, and that human PAS kinase can phosphorylate human ataxin-2. Further characterizing this interplay between PAS kinase and Pbp1/ATXN2 aid in understanding pathways required for proper glucose allocation during nutrient depletion, including reducing cell growth and proliferation when energy is low. In addition, it yields valuable insights into the role of ataxin-2 in the development of devastating ataxias.
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Olofsson, Madelen. "On the investigation of chemical parameters reflecting microbial activity linked to nutrient availability in forest soil." Doctoral thesis, Mittuniversitetet, Avdelningen för naturvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-25994.
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As agrarian society developed, the most fertile soils able to sustain the nutritional requirements needed for high crop yield were assigned to farming, while the more penurious soils were left to uphold the forest ecosystems. Some temperate forests are developed on acidic soils considered to be nutrient poor, as much of the inorganic nutrients are entrapped in poorly weatherable soil minerals and not easily accessed by plant roots. In an undisturbed ecosystem, the largest contribution of available nutrients comes from the recycling of organically bound nutrients via the decomposition of dead plant material. If biomass is removed, for instance with a more intensified exploitation of the forest ecosystems including whole tree harvesting, this source of nutrients is consequently decreased. The importance of soil mineral weathering as a source of nutrients, and especially that promoted by soil biota, is thereby emphasized. This thesis addresses biotic parameters associated with mineral weathering. Different aspects of soil solution sampling strategies and analysis of different organic ligands as well as biomarkers for the estimation of fungal biomass were investigated. These chemical parameters were also evaluated as indicators of microbial activity in relation to mineral nutrient availability in soil. With the assumption that the current nutrient status of a soil will affect the microbial interest of certain minerals as sources of inorganic nutrients, a mineral amendment trial was performed in a Swedish boreal forest soil. Overall, the amended soil presented good nutrient status, but with a possible shortage of iron. Due to this, it was hypothesized that the amended mineral with the highest iron content i.e. biotite would cause an elevation of microbial activity in its vicinity when compared to the bulk soil. The level of microbial activity in the vicinity of the amended minerals was evaluated via quantification of organic acids and siderophores, as well as estimation of fungal biomass and enzymatic activity. The highest microbial activity was measured for the O horizon of the investigated podzol, although nothing indicated an elevated association with the amended minerals. In the E horizon, however, elevation in microbial activity was observed in the vicinity of the biotite mineral when compared with bulk soil, although only a few of the investigated parameters differed significantly when evaluated separately. To enable this study, a highly sensitive analytical method employing liquid chromatography and mass spectrometry was developed to quantify a number of hydroxamate siderophores. On-line pre-concentration enabled detection of these organic ligands in the pico-molar range – a necessity when analyzing natural samples. Furthermore, an analytical method was developed for the estimation of fungal biomass via quantification of chitin-derived glucosamine, which also employed liquid chromatography and tandem mass spectrometry. Unlike currently available methods, the one presented in this thesis did not involve analyte derivatization, which resulted in high sample throughput while simultaneously avoiding complications involved with the additional derivatization procedure. The distribution of a group of organic ligands known as aromatic low molecular mass organic acids was also studied in a boreal forest podzol soil. Different sampling and samples preparation techniques, namely tension-lysimeters, soil centrifugation and liquid-soil extraction, were compared when analyzing soil solution components. Significant differences in analyte amount and species type were found between these sampling techniques. Some of the differences could be accounted for by variation in soil composition at different depths of the investigated podzol, but others could be attributed to structural differences within the studied analyte group. This clearly illustrated the intricacy of sampling and analysis when working with a sample matrix as complex and diverse as soil. As previously, liquid chromatography and mass spectrometry was used to quantify the analytes of interest. A highly sensitive analytical method was developed that was able to detect eleven aromatic low molecular mass organic acids in the nano-molar range. High selectivity was ensured by applying multiple reaction monitoring enabled by collision induced fragmentation of the analytes.FORE
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Nordstedt, Nathan P. "Isolation and characterization of novel bacterial strains to alleviate abiotic stress in greenhouse ornamental crops." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1617740819791342.
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Rocha, Silvia Regina Santos. "Procedimentos e avaliação química de parâmetros de interesse nutricional de espinafre comercializado na Bahia." Programa de Pós-Graduação em Química da UFBA, 2009. http://www.repositorio.ufba.br/ri/handle/ri/10014.
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O espinafre produzido e mais consumido no Brasil, denominado como espinafre da Nova Zelândia (Tetragonia expansa), difere significativamente do espinafre verdadeiro (Spinacia oleracea) produzido em muitos países do hemisfério norte. As diferenças ocorrem não apenas na classificação botânica, mas em muitas das características químicas dos vegetais. No presente trabalho, foram avaliados os teores de alguns nutrientes e antinutrientes contidos no espinafre comercializado na Bahia, sendo avaliados quatro diferentes procedimentos de digestão das amostras de espinafre com ácido nítrico em sistema aberto. Os resultados obtidos a partir dos diversos procedimentos de pré-tratamento da amostra foram comparados para os vários analitos investigados (Al, Ca, Fe, Cu, Zn, Mn, Mg) e indicaram vantagens da inserção de uma etapa de pré-digestão. Adicionalmente, foram realizados testes de extração dos metais sob investigação em água e em soluções com diferentes níveis de acidez na presença e ausência de agente quelante (ácido etilenodiaminotetracético – EDTA) para avaliação do nível de interação dos metais com o vegetal e, por conseguinte, a disponibilidade destes minerais. Os resultados levaram a acreditar que as interações de Mg(II), Cu(II) e Mn(II) com o espinafre seco eram fracas, enquanto que as interações com Al(III), Ca(II) e Fe(III) eram mais intensas, devido a condições mais drásticas (acidez da solução ou presença de quelante) foram necessárias para maximizar a extração destes metais. Ao considerar informações previamente reportadas sobre os elevados teores de oxalato em espinafre e seus efeitos antinutricionais, foram investigados os teores de oxalato em amostras secas oriundas de amostras de espinafre verdadeiro e espinafre da Nova Zelândia cultivado na Bahia, empregando permanganometria. Para tanto foram realizados estudos sobre as melhores condições para extração de oxalato variando a acidez da solução extratora e os resultados obtidos foram comparados com os apresentados na literatura. Finalmente, foram realizados testes para avaliação da possibilidade de enriquecimento de espinafre com íons metálicos a partir de sucessivas etapas de extração (dessorção) e concentração (sorção) do íon no vegetal. Pôde ser constatado que os maiores níveis de sorção (18 ± 3 mg g-1) e repetitividade foram obtidas para íons cálcio, possivelmente devido ao oxalato existente nos espinafres.
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Waggener, Amy Leigh Paerl Hans W. "The chlorophyll[-alpha] maximum of the Neuse River Estuary, North Carolina, U.S.A. nutrient dynamics and trophic interaction at the most productive region of the system /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,648.
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Thesis (M.S.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Marine Sciences." Discipline: Marine Sciences; Department/School: Marine Sciences. On t.p. "alpha" appears as Greek letter.
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Delaere, Fabien. "Détection des nutriments et contrôle central de la prise alimentaire." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10269.
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En relation avec sa position anatomique, la détection portale de nutriments se situe au coeur de l’impact de la composition nutritionnelle d’un repas sur la prise alimentaire et le métabolisme énergétique. Ainsi, la détection portale de glucose, produit par exemple en réponse aux protéines alimentaires, induit un signal nerveux à l’origine d’une induction de la satiété et d’une amélioration de l’homéostasie glucidique. Grâce à des travaux physiologiques et anatomiques chez le rat, nous proposons un modèle pour cette détection dans lequel deux modes interviennent, soit un transport et un catabolisme intracellulaire, soit une détection purement extracellulaire du glucose. La glycémie portale est détectée par l’un ou l’autre de ces mécanismes en fonction de sa différence avec la glycémie artérielle, reflet du statut nutritionnel et métabolique des individus. Un signal nerveux est ensuite initié dans les neurones périportaux, dont les axones aboutissent à proximité de la lumière veineuse. Les études immunohistochimiques réalisées ont permis de montrer que ce signal induit une activation cérébrale étendue en relation avec les effets multiples du glucose portal, dans le tronc cérébral, les systèmes sensoriels et cortico-limbiques, et l’hypothalamus. Dans ce dernier, la nature cellulaire de l’activation conforte notamment l’hypothèse de l’implication du signal glucose portal dans l’effet de satiété induit par les régimes riches en protéinesNutrient sensing in the portal vein occurs in a strategic location to relay the effects of the diet on food intake and energy metabolism. The portal sensing of glucose produced for instance in response to dietary proteins initiates a nervous signal that ultimately induces satiety and a better control of glucose metabolism. Our physiological and anatomical approaches enable us to propose a sensing model in which two different mechanisms can occur, involving either the intracellular transport and catabolism of glucose or a direct extracellular detection. Portal glycaemia is detected by one pathway or the other depending on its difference with arterial blood glucose, which reflects the nutritional and metabolic state of the subject. A nervous signal is then initiated in periportal neurons, whose axons terminate close to the venous lumen. Our immunohistochemical studies have shown that this signal induces a widespread activation in the brain that relates to the multiple effects of portal glucose appearance, in the brainstem, the sensory and cortico-limbic systems and the hypothalamus. In this latter area, the cellular nature of the activation supports the hypothesized central role of portal glucose appearance in the satiety effect of high-protein diets
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Memon, Jawed Akhtar. "Interaction between salinity and nutrients in cotton." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297670.
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Oates, Richard Hunter. "Phosphate-mineral interactions and potential consequences for nutrient cycling." Thesis, Online version of original thesis, 2008. http://hdl.handle.net/1912/2395.
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Wu, Kelvin Kwan Hoe. "Gene-nutrient interactions and risk of coronary heart disease." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614117.
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James, Karron. "TonB-protein interactions in nutrient uptake systems of «Escherichia coli»." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86777.
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Nutrient acquisition by Gram-negative bacteria requires strategies for passage across the outer membrane (OM). Because iron is a vital nutrient for bacteria, we aim to elucidate the molecular mechanism of its uptake.In an aerobic environment, ferric iron is predominant but exhibits low solubility. To overcome this challenge, bacteria import siderophores, ferric iron chelators. Siderophore import involves its binding to an OM receptor then to a periplasmic binding protein (PBP). Cytoplasmic membrane-embedded protein TonB, through its interaction with the periplasmic face of OM receptors, may provide energy to facilitate nutrient uptake.
To explore the molecular mechanism of TonB-dependent transport, we probed for conformational changes in FhuA, OM receptor for hydroxamate siderophores, in response to TonB binding. We defined epitopes for anti-FhuA monoclonal antibodies (mAbs) and monitored binding of these mAbs to FhuA with and without bound TonB. The most striking changes in binding kinetics were observed for mAb binding to extracellular loops of FhuA. We further explored these changes by conjugating a fluorophore, MDCC, to an extracellular loop of FhuA to monitor changes in fluorescence. Binding of TonB to FhuA quenched MDCC fluorescence.
Investigating events at another stage of TonB-dependent nutrient uptake, we previously discovered interactions between TonB and FhuD, PBP for hydroxamate siderophores. To determine whether such interaction occurs in other TonB-dependent uptake systems, we investigated binding of TonB to BtuF, PBP for cyanocobalamin. By phage display, we predicted a TonB-BtuF interaction by identifying potential binding residues on each protein. Further, we confirmed in vitro interaction between these proteins. TonB-BtuF binding stoichiometry was 1:1 and independent of cyanocobalamin.
In summary, binding of TonB to the periplasmic face of FhuA induced conformational changes in extracellular loops of the receptor that may serve to promote vectorial transport of siderophore. In addition, we have identified a novel, cyanocobalamin-independent interaction between TonB and BtuF. This interaction could serve to situate BtuF to efficiently encounter, bind and deliver substrate for uptake into the cytoplasm.
L'acquisition d'éléments nutritifs par les bactéries gram-négatives nécessite des stratégies de transport au travers de la membrane externe. Le fer étant un élément essentiel pour les bactéries, nous travaillons à élucider le mécanisme moléculaire de ce transport.
En milieu aérobique, le fer se trouve principalement sous sa forme ferrique qui est peu soluble. Pour surmonter cet obstacle, les bactéries importent des sidérophores, un type de chélateurs du fer ferrique. L'acquisition des ces sidérophores implique leur liaison par un récepteur de la membrane externe et par une protéine périplasmique de liaison. L'énergie nécessaire au transport de sidérophores à travers la membrane externe pourrait être fournie par TonB, une protéine de la membrane cytoplasmique qui se lie à la face périplasmique du récepteur de la membrane externe.
Pour étudier le mécanisme moléculaire du transport TonB-dépendant, nous nous sommes attardés aux changements de conformation que FhuA, le récepteur de sidérophores hydroxamiques situé dans la membrane externe, subit en réponse à sa liaison avec TonB. Des épitopes pour anticorps monoclonaux contre FhuA ont été sélectionnés et leur liaison avec FhuA, en présence et en absence de TonB, a été testée. Les changements les plus notables ont été remarqués avec les anticorps se liant aux boucles extracellulaires de FhuA. Pour confirmer ces changements, un fluorophore, le MDCC, a été conjugué aux boucles externes de FhuA et l'intéraction entre les deux protéines engendre une extinction de fluorescence.
En étudiant d'autres étapes du transport TonB-dépendant, des intéractions entre TonB et FhuD, une protéine périplasmique de liaison de sidérophores hydroxamiques, ont été découvertes. Pour vérifier si des intéractions similaires existaient dans d'autres systèmes d'acquisition TonB-dépendant, nous avons investigué les intéractions entre TonB et BtuF, la protéine périplasmique de liaison de la cyanocobalamine. L'identification, par phage display, de résidus clés sur TonB et BtuF nous a permis de prédire une intéraction entre ces deux protéines, que nous avons confirmée par la suite in vitro. La stoechiométrie de liaison a été établie à 1 :1 et est indépendante de la présence de cyanocobalamine.
En conclusion, la liaison de TonB à la face périplasmique de FhuA induit des changements de conformation dans les boucles extracellulaires du récepteur qui pourraient servir au transport unidirectionnel de sidérophores. De plus, nous avons découvert une nouvelle intéraction entre TonB et BtuF qui est indépendante de la présence de cyanocobalamine. Cette intéraction positionnerait BtuF de façon à maximiser la rencontre, la liaison et le transport de son substrat jusqu'au cytoplasme.
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Donahey, Geneviève A. "Pairwise Antibiotic Interactions on Escherichia coli Under Changing Nutrient Conditions." Scholarship @ Claremont, 2016. http://scholarship.claremont.edu/cmc_theses/1314.
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Due to high rates of emerging antibiotic resistant bacteria, research into combatting these “superbugs” has focused on engineering more effective treatments for bacterial infections, including pairing antibiotics having varied mechanisms of action to elicit a stronger antimicrobial response than a single antibiotic treatment. Previous studies have characterized pairwise antibiotic interactions as having synergistic, additive, or antagonistic relationships, suggesting the possibility that many factors influence the resulting response. As an extension of the research done on paired antibiotic interactions, this work endeavored to examine whether changing nutritional environments had an effect on documented synergistic relationships between various groups of antibiotics. To corroborate previous studies, antibiotics from the β lactam (targeting cell wall synthesis) and aminoglycoside (targeting protein synthesis) families were chosen as test subjects and paired with antibiotics from other classes under varied nutrient conditions. Streptomycin (STR) and Amikacin (AMK) were two aminoglycosides tested in their relationship to Ciprofloxacin (CPR), a fluoroquinolone (targeting DNA replication). The relationships between the aminoglycosides and CPR remained consistently synergistic in various media, including two complex, undefined media, LB and yeast extract (YE), and dilution of both media with a saline solution to half-strength. In contrast, the selected β lactams Piperacillin (PIP) and Ampicillin (AMP) did not show a previously documented synergy with the macrolide (targeting protein synthesis) Erythromycin (ERY), and alterations to the culture medium vastly affected the PIP/ERY combined relationship. Collectively, these results suggest that antibiotic interactions are not based on a singular mechanism, and that these relationships may be able to be manipulated through environmental factors such as changing nutritionalenvironments. A multi-faceted pathway for manipulating drug interactions may be key in increasing the efficacy of antibiotic treatment plans.
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Bertoncello, Ricardo. "Restauração ecológica e processos estruturadores de comunidades vegetais." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/41/41134/tde-28092016-102207/.
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Interações interespecíficas são consideradas importantes forças estruturadoras da vegetação. Enquanto a competição aparentemente prevalece em ambientes com menor estresse abiótico, a facilitação tende a aumentar em importância em ambientes de maior estresse. Consequentemente, é esperado que a facilitação desempenhe um papel importante em áreas tropicais degradadas, nas quais as condições abióticas, envolvendo altos níveis de irradiação, temperatura e evapotranspiração, são muito distintas das condições ótimas para a maioria das espécies florestais. Além disso, face à complexidade dos processos estruturadores de comunidades florestais tropicais altamente diversas, os ecólogos têm percebido a necessidade de simplificação. Um caminho promissor para isso é por meio do uso de características funcionais, que podem ser medidas para qualquer espécie e comparadas em diferentes sistemas e locais. No entanto, em áreas degradadas ainda é incerta a relação entre as características funcionais e o desempenho das espécies. Neste contexto, planejamos um projeto de restauração na planície costeira do sudeste brasileiro para comparar o crescimento e a sobrevivência de mudas de árvores plantadas em diferentes densidades (sistema isolado ou sistema agregado) em um experimento fatorial com adição de nutrientes. No primeiro capítulo analisamos a sobrevivência, altura, diâmetro ao nível do solo e projeção da copa de 4.132 mudas de 19 espécies de diferentes classificações sucessionais, durante um período de 18 meses. Usamos modelos de efeitos mistos para analisar a relação entre o desempenho de espécies e os tratamentos e selecionamos os melhores modelos utilizando o critério de informação de Akaike (AIC). Verificamos uma maior sobrevivência nos sistemas agregados para as espécies não-pioneiras, indicando o predomínio do processo de facilitação. Em contrapartida, constatamos um menor crescimento em diâmetro nos sistema de plantio agregado, indicando o predomínio de competição. A adição de nutrientes não afetou a sobrevivência nos sistemas agregados, mas, surpreendentemente, teve um efeito negativo sobre as plantas isoladas. Além disso, a adição de nutrientes teve um efeito positivo sobre crescimento, diâmetro e projeção da copa nos sistemas de plantio agregado (indicando a redução da competição), especialmente para espécies pioneiras. Uma vez que o estabelecimento de espécies não-pioneiras em áreas degradadas pode ser bastante difícil, a facilitação para a sobrevivência dessas espécies em sistemas agregados pode ser utilizada como instrumento para melhorar os modelos de restauração. No segundo capítulo utilizamos algumas características funcionais que são facilmente mensuráveis para investigar sua relação com o crescimento e sobrevivência das mudas. Além disso, testamos o efeito das interações interespecíficas na relação das características funcionais com o desempenho das plantas. Para espécies pioneiras, uma maior área foliar específica (SLA - Specific leaf area), foi relacionada com uma maior taxa de sobrevivência. Entretanto, ao considerarmos as relações interespecíficas (sistemas agregados), maior SLA foi relacionada com uma menor taxa de sobrevivência. Em geral, as características funcionais explicaram apenas parcialmente o desempenho de mudas no contexto de restauração de áreas degradadas. Nosso trabalho contribuiu para a discussão sobre o potencial da aplicação prática da abordagem funcional na escolha das espécies para a recuperação de áreas degradadas. O caráter manipulativo da restauração ecológica baseada no plantio de mudas amplia as perspectivas para implementar experimentos que visem testar novas hipóteses em ecologia e refinar modelos de restauraçãoInterspecific interactions are considered to be important structuring forces in early successional vegetation. Whereas competition seems to prevail in less severe environments, facilitation tends to increase in importance in harsh environments. Hence, facilitation is expected to play an important role in degraded tropical areas with high irradiance, heat loads, and evapotranspiration, where conditions are far from optimum for most forest species. Moreover, in order to understand complex structuring process of high diverse tropical forests, ecologists have realized the need for simplification. A promising way to do that is through the use of functional traits, which can be measured for any species and compared in different systems and different locations around the world. However, in these conditions, little is known about the role of species interaction on the relation of functional traits and species performance. In this scenario, we planned a restoration project on the southeastern Brazilian coastal plain to compare growth and survival of tree seedlings planted at two densities (isolated or aggregated) in a factorial experiment with nutrient addition. In the first chapter we analyzed survival, height, ground level diameter, and crown projection of 4,132 saplings from 19 species that ranged along a successional gradient, over an 18-month period. We used mixed-effect models to analyze the relationship between species performance and treatments, and Akaike\'s information criterion (AIC) to select the models. The best model showed higher survival in aggregated plantations (indicating facilitation) for non-pioneer species. In contrast, we found lower diameter growth in aggregated plantation (indicating competition). Fertilizer addition did not affect survival in clusters, but, surprisingly, it had a negative effect on isolated plants of both pioneer and non-pioneer species. On the other hand, fertilizer addition had a positive effect on diameter and crown projection growth in aggregated plantations (reducing competition), especially for pioneer species. Thus, whether facilitation or competition was the predominant interaction depended on the response analyzed. We concluded that, as establishment of non-pioneer species in disturbed sites can be challenging, restoration designs could take advantage of higher survival rates in clusters and use resource addition to ameliorate growth and decrease competition for limited resources. In the second chapter we used the core simple-measurable traits to investigate whether functional traits were related to growth and survival and whether there was a difference in the effect of the functional traits on plant performance of isolated individuals or of individuals subjected to interaction with neighbors. Our main findings were that for pioneer species, the greater the specific leaf areas (SLA), the greater the survival rates, but, under aggregated conditions, the greater the SLA the lower the survival rates. However, functional traits only partially explained saplings performance in a restoration context and more research is needed to understand its role in predicting seedlings outcomes, especially considering the potential applicability of this methodological approach. The manipulative character of ecological restoration broadens perspectives to use experiments to generate and test new hypotheses in ecology and to refine restoration models
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Shan, Shan. "The controls of nutrient limitation on resource allocation belowground." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1580078025127756.
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Majoni, Sandra. "Effects of shelf-life on phytonutrient composition in stored non-alcoholic beer." Menomonie, WI : University of Wisconsin--Stout, 2006. http://www.uwstout.edu/lib/thesis/2006/2006majonis.pdf.
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Rantanen, Leena. "Interactions between effects of air pollutants and nutrient status of trees." Thesis, Lancaster University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385651.
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Kraus, Tamara Esther Caroline. "Tannins and nutrient dynamics in forest soils : plant-litter-soil interactions /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.
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Barthelemy, Hélène. "Herbivores influence nutrient cycling and plant nutrient uptake : insights from tundra ecosystems." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-120191.
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Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.
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Liess, Antonia. "Nutrient Stoichiometry in Benthic Food Webs – Interactions Between Algae, Herbivores and Fish." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6933.
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Asandei, Ancuta. "Global warming : carbon-nutrient interactions and warming effects on soil carbon dynamics." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/17537.
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In order to predict how terrestrial ecosystems will respond to global change, there is growing recognition that we need to better understand linkages between plant and soil processes. Previously the factors and processes with potential to influence the terrestrial carbon (C) cycle have been investigated in isolation from each other. This study investigated the interactions of nutrient availability and warming in controlling the soil carbon dynamics, with regards to the fate of already sequestered carbon in soil, under conditions of increasing atmospheric temperatures. The project objectives were addressed by three independent experiments designed to explain specific components of the carbon-nutrient cycle interactions, and the findings brought together to describe the implications for future soil carbon storage. The main measurements collected throughout this project included soil carbon dioxide (CO2) fluxes, partitioned into autotrophic and heterotrophic components, net ecosystem exchange and respiration fluxes, and background soil moisture and temperature data, backed by gas, soil and biomass analyses. In the two field experiments, these measurements were taken from plots with or without any inorganic nutrient additions or in the presence or absence of legumes providing biological nitrogen addition to the ecosystem. In the laboratory, temperature and nutrient availability were manipulated within the ecosystem. The reduction in decomposition rates, without reduction of productivity as a result of inorganic nutrient additions, indicated the potential for increasing C storage. There was also evidence that nutrient availability controls the strength of the link between plant and soil processes in semi-natural grasslands. The yields, decomposition rates and soil C fluxes recorded in the presence and absence of legumes provided some evidence of N2 fixation, improving ecosystem productivity and soil properties while reducing soil C effluxes, in a managed grassland. In the laboratory, the warming of soils from lysimeters with and without plants, receiving or not receiving fertiliser, supported the findings from field experiments regarding the importance of the soil-plant link in controlling C fluxes. However, C stocks and δ13C analyses showed that over a year’s worth of warming and nutrient manipulations made little difference to the amount of C stored in the soil, indicating that edaphic factors have greater control over the response of C dynamics to increased temperatures.
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Busch, Johannes Wilhelm. "New Methods for Describing Plant and Herbivore Response to Complex Multiple-Nutrient Interactions /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487931993467921.
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Perkins, Denise Mary. "Isolation of and interaction of nutrients with the linoleoyl-coa desaturase complex." Thesis, Rhodes University, 1990. http://hdl.handle.net/10962/d1018264.
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The termina1 enzyme in the linoleoyl-CoA desaturase enzyme complex, delta-6-desaturase was implied in the control of cell proliferation in cancer cells. One of the aims of this study was to isolate the terminal enzyme. It was decided that in order to isolate this enzyme it was first necessary to isolate the entire complex and then to enzymatically solubilise the first two components of the complex i e cytochrome b5 reductase and cytochrome b5 from the complex resulting in a pure delta-6-desaturase . The first two components were isolated and purified using simplified and easily reproducible methodologies which could be utilised in the final purification of delta-6- desaturase. The entire enzyme complex, linoleoyl-CoA desaturase was also isolated in a pure form and this pure complex was used to attempt to isolate delta-6-desaturase. The terminal enzyme was isolated with some cytochrome b5 still bound to it. The methods used had proven to be successful and with some modifications should yield a pure enzyme. Zinc and GLA were known to play a role in the inhibition of cancer cell proliferation and zinc was hypothesised to inhibit cell growth by stimulating the activity of the linoleoyl-CoA desaturase enzyme complex which is involved in the regulation of cell proliferation. GLA is the product of the reaction that this enzyme complex catalyses and GLA has been shown to inhibit cancer ce ll growth. The effect of GLA on cell growth and linoleoyl-CoA desaturase activity was thus investigated. Results showed that both zinc and GLA inhibited cell growth and that the combined addition of zinc and GLA generally resulted in the inhibition of cell growth and the activation of linoleoyl-CoA desaturase activity in the BL-6 cells while having a less pronounced effect on the LLCMK cells. The results of this study support the hypothesis that zinc may be a cofactor of linoleoyl-CoA desaturase.
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Messervy, Faye Carol. "The interacting effects of pattern of nutrient supply and defoliation on plants." Thesis, University of Sussex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442433.
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Wilson, Alan Elliott. "Cyanobacteria-Grazer Interactions: Consequences of toxicity, morphology, and genetic diversity." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04072006-125946/.
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Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2006.Klausmeier, Christopher, Committee Member ; Montoya, Joseph, Committee Member ; Snell, Terry, Committee Member ; Sarnelle, Orlando, Committee Member ; Hay, Mark, Committee Chair.
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Paudel, Bhanu. "Interactions between suspended sediments, nutrients and freshwater inflow in Texas estuaries." Thesis, Texas A&M University - Corpus Christi, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3632597.
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The objectives of the present study were to identify the effects of freshwater inflow (FWI) on sediment transport and nutrients supply to estuaries, and the effects of sediments on nutrient supply at sediment-water interface. The Nueces River and its estuary, the Guadalupe River and its estuary, and the Lavaca-Colorado Estuary were selected for field studies. Laboratory experiments were conducted to test the study hypotheses, and data was analyzed using multivariate modeling and statistical approaches.
In the Guadalupe Estuary, variability of suspended solids and nutrients were correlated with FWI, whereas in the Nueces and Lavaca-Colorado Estuary they were related with seasonal differences. Suspended solids in the estuaries increased during frontal events and during windy days. In some of the field samplings, stations closer to the Gulf of Mexico had higher suspended sediments than the stations closer to the river. The increase in suspended sediments increased ammonia concentration in the Guadalupe Estuary, phosphorus and silicate concentrations in the Nueces Estuary, and silicate concentration in the Lavaca-Colorado Estuary. The presence of silicate minerals in the estuaries maintains silicate concentration as well. Organic matter and calcium carbonate shells in sediments of the estuaries can bind phosphate, thus, may have played role in decreasing phosphate concentration in the water. Guadalupe River sediments, when transported to the estuary, can release ammonia at higher concentrations the river water concentration. Salinity in the estuary, thus, has a significant role in controlling nutrient concentrations.
The release of ammonia by organic matter decomposition was lower in the Guadalupe Estuary than in the Nueces Estuary. The high inflow volumes in the Guadalupe Estuary may have washed away organic matter from the sediments and may have disturbed bacterial community resulting in the lower release of ammonia from Guadalupe Estuary sediments. The research performed here demonstrates the importance of sediments, organic matter, and inflow in maintaining nutrient concentrations in estuaries. Fluctuation of these nutrients can affect water quality, and hence, may influence the ecology of the estuary.
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Fulton, Barry A. Brooks Bryan William. "Assessing interactions between nutrients and toxicity influences of nitrogen and phosphorus on triclosan toxicity to the aquatic macrophyte "lemna gibba" /." Waco, Tex. : Baylor University, 2009. http://hdl.handle.net/2104/5351.
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Shatwell, Tom. "Interactive effects of nutrients and physical factors on phytoplankton growth." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16877.
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Phytoplanktonarten unterscheiden sich in ihren Ansprüchen hinsichtlich Ressourcen wie Nährstoffe, Licht und andere physikalische Faktoren. Wechselwirkungen zwischen Nährstoffen und physikalischen Faktoren beeinflussen daher die Artenzusammensetzung einer Phytoplanktongemeinschaft. In der vorliegenden Arbeit wurde der Einfluss von Temperatur und Photoperiode auf das Phytoplanktonwachstum in Abhängigkeit vom Lichtregime und dem Angebot an Phosphor (P) und Silizium (Si) untersucht. Hierfür wurden Wachstums- und Konkurrenzexperimente unter Laborverhältnissen mit Stephanodiscus minutulus, Nitzschia acicularis (beides Bacillariophyceae) und Limnothrix redekei (Cyanophyceae) durchgeführt, ein Modell der Faktorinteraktionen entwickelt sowie ökologische Langzeitdaten des Müggelsees (Berlin) statistisch ausgewertet. Die Effekte von Temperatur und Photoperiode auf die Wachstumsraten unterschieden sich nicht zwischen konstantem und fluktuierendem Licht. Die Auswirkungen der Photoperiode und der Lichtfluktuationen auf die Wachstumsraten waren hierbei additiv. Der Grad der Limitation der Wachstumsraten durch P oder Si wurde durch die Photoperiode nicht signifikant beeinflusst. Wechselwirkungen zwischen Temperatur und P oder Si waren hingegen komplex und artspezifisch. Unabhängig davon, ob die Wachstumsraten durch P, Si oder fluktuierendes Licht gesteuert wurden, war S. minutulus konkurrenzstärker bei niedrigeren Temperaturen und N. acicularis bei höheren Temperaturen. Zusammenfassend zeigen die Ergebnisse, dass die Faktorinteraktionstypen artspezifisch sind, die Adaptation der Arten widerspiegeln und so zur Nischen-Differenzierung beitragen. Kenntnisse dieser Wechselwirkungen fördern deshalb unser Verständnis der Phytoplanktondiversität und ermöglichen es, Reaktionen des Phytoplanktons auf Klimaerwärmung und Trophieveränderung, die mit einer Verschiebung der Verhältnisse zwischen Nährstoffen, Temperatur und Licht einhergehen, besser vorherzusagen.Phytoplankton species have different resource requirements and different sensitivities to important growth factors. Interactions between nutrients and physical factors, such as temperature and light should therefore influence the species composition. Because these interactions are poorly understood, this study investigated the interactive effects of temperature and photoperiod on phytoplankton growth controlled by fluctuating light, phosphorus (P) and silicon (Si). Growth and competition experiments were performed in the laboratory on Stephanodiscus minutulus, Nitzschia acicularis (both Bacillariophyceae) and Limnothrix redekei (Cyanophyceae). A model of factor interactions was developed and long-term field data from Lake Müggelsee (Berlin) were statistically analysed. Temperature and photoperiod had the same influence on growth under fluctuating light as they did under constant light. The photoperiod and short term light fluctuations caused by mixing had additive effects on growth. P and Si interacted strongly with temperature with respect to growth, but less with the photoperiod. The Droop relation fitted to S. minutulus but not N. acicularis. The Monod equation could not sufficiently account for non-steady dynamics of diatom growth under Si limitation, underestimating uptake rates and overestimating uptake affinity. Estimates based on the Monod model may therefore considerably underestimate the degree of Si limitation. The types of factor interactions were generally species-specific, reflected niche adaptation and enhanced niche differentiation. Interactions between nutrients and physical factors are relevant to growth during spring and contribute to the phytoplankton composition. Understanding the interactions should improve our knowledge of phytoplankton diversity and increase our ability to predict phytoplankton response to climate and trophic change, which shift the relationship between nutrients, temperature and light.
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Brown, Sandra Jean. "Soil fertility, nutrient dynamics and socio-economic interactions in the Middle Mountains of Nepal." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25023.pdf.
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Hardison, Amber Kay. "Interactions between macroalgae and the sediment microbial community : nutrient cycling within shallow coastal bays /." W&M ScholarWorks, 2009. http://web.vims.edu/library/Theses/Hardison09.pdf.
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Hines, Jessica. "Nutrient and structural effects of detritus on food web interactions in an intertidal marsh." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1523.
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Thesis (M.S.) -- University of Maryland, College Park, 2004.Thesis research directed by: Dept. of Entomology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hovard, Peter. "The role of cognitive, sensory and nutrient interactions in satiation and satiety : considering consumers." Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/63963/.
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Previous research from the Sussex Ingestive Behaviour Group suggests that satiety beliefs generated by product information and satiety-relevant sensory characteristics (thick consistency and creamy flavours) can enhance the satiety response to covertly added energy in beverages. However these characteristics in low-energy beverages can generate rebound hunger effects. This thesis explored whether this enhanced-satiety concept can be translated to real consumers. Study 1 examined the extent of energy reduction that could be tolerated without rebound hunger effects. The original enhanced satiety concept was not replicated, although there was tentative evidence that energy compensation was more accurate for small energy additions. Study 2 explored whether enhanced satiety would prevail following repeated exposures in consumers' own homes. Enhanced satiety was found before and after exposure. Additionally focus groups suggested that diet-concerned consumers may be particularly interested in such products. Therefore in Study 3 this population, represented in the literature by those reporting high dietary restraint, was studied suggesting that those high in restraint and disinhibition compensated more accurately for energy in unenhanced beverages. A final complication for consumers is that believed healthy foods are often overconsumed. Two final studies demonstrated that health labels generated beliefs about the sensory experience and expected satiation and satiety of beverages. Tasting overrode the effects of these beliefs, although expectation-experience congruency led to assimilation of healthy beliefs, and indulgent-based fullness. Portion size selection was unaffected. Together the findings from these studies suggest that the enhanced satiety concept may have some utility in the real world, although it remains unclear as to how little caloric content can be tolerated whilst still enhancing satiety, and whether diet concerned consumers would benefit. Finally whilst health information may have a role in appetite expectations the interaction with sensory experience is important for generating overall product evaluations, and sensory experience is likely to override label information in dictating portion size selection.
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Di, Palo Francesca. "Plant species and soil nutrient interactions along primary successions: the role of ecological stoichiometry." Thesis, Ulster University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.650087.
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A long-standing question in plant ecology remains about what underlying mechanisms are responsible for the distribution of plant species across environmental gradients. Most plant ecologists agree that the answer lies within the concept of 'niche' and thus in the set of driving 'key-resources' for plant growth under specific environmental conditions. Here I examine two key soil resources: nitrogen (N) and phosphorus (P). I ask whether changes in the availability of Nand P in soils may predict changes in critical plant element ratios (i.e. C:N:P stoichiometry). Very few studies have used an 'ecological stoichiometric' approach to address whether changes in soil nutrient availability and content could explain changes in plant C:N:P tissue stoichiometry along strong soil development gradients. I address this question using four ecological successions distributed across Europe where I measured C:N:P stoichiometry of roots, stems and leaves of 72 plant species. If plant nutrient stoichiometry is determined by Nand P uptake in response to local growth conditions (i.e. pioneer vs. advanced soil development stages), I would expect soil and plant N:P ratios positively related along the soil chronosequence. Overall my results show that soil N:P ratios strongly increased along the gradient of soil development from pioneer to advanced successional stages. However, I found that neither changes in soil nutrient availability, nor total soil nutrient content or soil N:P stoichiometry were significantly related to changes in plant nutrient stoichiometry. Instead I found that plant functional group identity (i.e. legumes vs. grasses vs. forbs) has a strong control over changes in plant N:P ratios regardless of the temporal stage of the ecological succession. I have also found that carbon:nutrient ratios (either C:N or C:P) along primary successions are quite variable and are partly related to changes in soil nutrient status, plant functional group identity and plant compmiment (e.g. roots vs. leaves). The lack of any correlation between soil and plant stoichiometry could be attributed to (1) the presence of internal mechanisms of plant nutrient and carbon use efficiency, (2) belowground ecophysiological processes (e.g. root exudation), and (3) plant-microbial interactions (e.g. symbiosis) all which can affect plant nutrients uptake and nutrient reallocation within compmiments. Finally, my study shows that wild-plant species seem to have a high-degree of internal nutrient regulation (i.e. high stoichiometric homeostasis), whose underlying mechanisms need to be better understood because may be key to better understand plant distribution along environmental gradients
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Sidhu, Manjinder. "Interactions between heavy metals and mineral nutrients in the moss rhytidiadelphus squarrosus." Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317966.
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Queiroz, Renan Batista. "Adubação com enxofre, nitrogênio, cálcio e potássio afetando a interação entre Tuta absoluta e o tomateiro." Universidade Federal de Viçosa, 2011. http://locus.ufv.br/handle/123456789/3917.
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The nutrients used for plant fertilization affect their susceptibility to insect herbivores. Among the major pests of tomato in the world is a leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). Thus, the aim of this study was to determine the influence of plant fertilization with calcium, sulfur, nitrogen and potassium in reproduction, growth, survival and damage of T. absoluta. This study was conducted in a greenhouse. The experimental design was randomized blocks with nine treatments and five replications. The treatments consisted of fertilization levels of deficiency and excess calcium, sulfur, nitrogen and potassium. One treatment with normal fertilization was established beyond these levels. The eggs from T. absoluta were transferred for the leaves of tomato a month after the start of the experiment. The number of surviving insects, the developmental stage of insects and the number of mines per leaf were evaluated daily. The contents of nutrients were determined in leaves of tomato. Among the nutrients studied, only the doses of sulfur and nitrogen fertilizer used in the affected T. absoluta. The reproduction of T. absoluta was lower in plants with normal fertilization, higher the mortality of larvae and these plants suffered less damage than those with nutritional deficiency. The maximum reproductive performance of T. absoluta occurred in plants with nutritional deficiency. The plants with higher levels of nutrients in leaves were less susceptible to T. absoluta.
Os nutrientes utilizados na adubação das plantas afetam sua suscetibilidade aos insetos herbívoros. Entre as principais pragas do tomateiro no mundo está a traça Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). Assim, o objetivo deste trabalho foi determinar a influência da adubação das plantas com cálcio, enxofre, nitrogênio e potássio na reprodução, desenvolvimento, sobrevivência e danos de T. absoluta. Este trabalho foi conduzido em casa de vegetação. O delineamento experimental foi em blocos casualizados com nove tratamentos e cinco repetições. Os tratamentos foram constituídos de níveis de adubação em deficiência e em excesso de cálcio, enxofre, nitrogênio e potássio. Além destes níveis estabeleceu-se um tratamento com adubação normal. Um mês após o início do experimento, foram transferidos ovos de T. absoluta para as folhas do tomateiro. Diariamente avaliaram-se o número de insetos sobreviventes, o estádio de desenvolvimento dos insetos e o número de minas por folha. Foram determinados os teores de nutrientes nas folhas do tomateiro. Dos nutrientes estudados apenas as doses de enxofre e de nitrogênio usadas na adubação afetaram T. absoluta. Nas plantas com adubação normal foi menor a reprodução de T. absoluta, maior a mortalidade larval e estas plantas sofreram menores danos do que aquelas com deficiência nutricional. O máximo desempenho reprodutivo de T. absoluta ocorreu em plantas com deficiência nutricional. As plantas com maiores teores de nutrientes nas folhas foram menos suscetíveis a T. absoluta.
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Dinkeloo, Kasia. "New Tools to Understand Mechanisms of Nutrient Transfer from Plants to Biotrophic Pathogens." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/97521.
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The interaction between Arabidopsis and its natural downy mildew pathogen, Hyaloperonospora arabidopsidis (Hpa), provides a model for understanding how oomycetes colonize plants. Hpa is a model organism for many highly destructive oomycete pathogens and transcriptomics of this interaction have been well-documented. However, the material in these studies has been derived from infected leaves that contain a mix of pathogen-proximal and pathogen-distal plant cells. The most direct interactions between Arabidopsis and Hyaloperonospora arabidopsidis occur in haustoriated cells- where the pathogen can secrete effectors and acquire nutrients needed for successful colonization and reproduction. These cells are difficult to isolate due to their limited number and ephemeral nature. I have developed a method to isolate the translatome (i.e., mRNAs associated with ribosomes) of pathogen-proximal cells. This method utilizes translating ribosome immuno-purification technology (TRAP), regulated by both pathogen-responsive and tissue-specific promoters, to isolate mRNAs that are being translated in pathogen-proximal cells. Compared to "bulk" transcriptomics of material isolated from homogenized leaves, this method will enrich for transcripts that are differentially expressed, and translated, in pathogen-proximal cells. From this method, RNA was isolated in amount and quality sufficient for sequencing. This sequencing data will enable the discovery of plant genes that may be manipulated by the pathogen to suppress defense responses and extract nutrients.Ph. D.
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Hillmer, Kiekebusch Ingrid Andrea. "Scales of interactions between physical processes, primary producers and nutrients in aquatic ecosystems." University of Western Australia. Centre for Water Research, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0177.
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[Truncated abstract] Estimating internal biogeochemical fluxes is essential to the understanding of the dynamic of aquatic ecosystems. Different ecological approaches have been used to gain insight into the internal cycling, but success has been limited. A critical point is the identification of the characteristic scales of patterns and the underlying processes affecting the behaviour of biological and chemical species. Failing to capture these scales leads to misinterpretation of field and numerical data. In this study, key aspects in the design of ecological surveys are identified to ensure that the internal biogeochemical processes are well represented. In the first part of this thesis, a 1D reaction-diffusion-advection equation is used to investigate the formation of patterns and relevant time and spatial scales. This is used to define an approach for the determination of a critical domain size that allows differentiation of the role of local and internal cycling from advective fluxes across the open boundaries in a shallow coastal ecosystem. By using a 3D numerical model, in conjunction with an extensive field data set, it is shown that domain sizes must be larger than this critical value in order to capture the patterns generated within the system. For smaller domains, transport processes control the evolution of the system across the boundaries misleading the interpretation of the internal ecological dynamics. The study of the influence of boundary fluxes on ecological patchiness was motivated by the need to define the size of the domain necessary for the assessment of the impact of a sewage outflow on a coastal regime. The quantification of biogeochemical processes has proven to be difficult to achieve especially under conditions of high spatial and temporal hydrodynamic and biogeochemical variability. In the second part of this thesis, a Lagrangian experimental design is employed to estimate biogeochemical rate coefficients in situ. A set of four drogues and a cross-transect sampling design is used to capture the patchy distribution of phytoplankton and nutrient species, and high transport and mixing rates. ... Total chlorophyll from both models shows similar behavior when the variability in the 3D model, expressed as Chlamax/Chlamin, is low. When Chlamax/Chlamin is high, the difference between the biomass predicted by the two models reaches 30% due to the generation of localised patches. Comparison of the 1D and 3D results highlights the need of using models that are able to resolve the spatial complexity to some extent, as the use of averaged properties may produce misleading results. This is especially important in the presence of patches with differential physiological and biogeochemical characteristics, and nonlinear processes, in which case biomass average is not necessarily linearly related to the averaged environment.
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Hänninen, K. (Kaarina). "Tree - cover crop interactions: birch growth, competition and soil properties." Doctoral thesis, University of Oulu, 2002. http://urn.fi/urn:isbn:9514267184.
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Abstract
The main objective of this thesis was to investigate tree - cover crop interactions and soil response in an intercropping system, in which leguminous and grass cover crops were used with birch (red-leaved Downy birch Betula pubescens L.). The investigation was conducted in two field experiments in a nursery and in a greenhouse experiment. In the latter the effect of the water supply in interspesific competition was also investigated. The cover crops in the field experiments were perennial clovers Trifolium pratense L., T. repens L. and T. hybridum L. and annual clovers T. incarnatum L., T. resupinatum L. and T. subterraneum L. and perennial Festuca rubra L. The height, stem diameter, leaf area and nutrient status of the birch were determined, as well as soil nutrient status and microbial characteristics. The cover crops in the greenhouse experiment were T. repens, T. subterraeum and F. rubra. The biomass, height, leaf area, leaf area index, specific leaf area and N concentration of the birch, the biomass and N concentration of the cover crops were measured, and soil N and microbial characteristics, as well. Bare ground was the control in all the experiments.
The perennial clovers and Festuca strongly decreased the birch growth and nutrient status, but the annual clovers sown in midsummer in the field experiments provided about as good growth as bare ground. In the greenhouse experiment all cover crops were effective competitors with the birch. The soil NO3-N was, in general, the highest on bare ground and second highest in the annual clover plots. Though there were, in general, only minor differences in the soil nutrient concentrations between the treatments, there were significant differences in the tree growth and nutrient concentrations. The interspecific competition in this kind of intercropping system is mainly belowground. The growth reduction in the birch was mainly due to competition for nitrogen but water seems to play an important role in regulating the competitive interaction between the birch and cover crops. The competition for these resources seems to be most crucial at the beginning of the growing season. The microbial biomasses and soil respiration were greatest in the Festuca and perennial clover treatments, which may indicate that microorganisms together with these cover crops may seriously compete with birch for nutrients.
Intercropping system is complex and comprises both negative and positive influences. In order to minimize negative competition effects, the cover crop should be non-competitive or the ground should be kept free of vegetation at the beginning of the growing season. By improving soil microbial characteristics, the vegetative ground covers make this cropping system one possiblity towards sustainability in the long-term.
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Tekinay, Ahmet Adem. "Dietary interactions influencing feed intake, nutrient utilisation and appetite regulation in the rainbow trout, Oncorhynchus mykiss." Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/1974.
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Dietary factors are one of the most significant considerations in the regulation of appetite in fish since dietary nutrient and energy concentration modulate feed intake in the short and longer term. These interactions may also be important from a commercial aspect, since the objective of aquaculture is to obtain maximum growth, feed efficiency and consumer acceptance of the product. This thesis addresses the major dietary components which are likely to influence appetite in rainbow trout. These include dietary lipid level, carbohydrate content and degree of complexity as well as energy density and protein/energy ratio. Experimental data is presented which examines the influence of such factors on reed intake, growth performance, nutrient utilisation, gastric evacuation rate, return of appetite and changes with respect to the postprandial level of circulating plasma metabolites. It is proposed that rainbow trout have the capacity to regulate feed intake within specific constraints. On the other hand, trout become obese when offered high oil diets and fail to control feed intake in the short term, possibly due to the palatability of lipids. Regulation may also appear at a metabolic level following accumulation of lipids in adipose tissue. Gastric evacuation rate was probably the main factor in the short term influencing feed intake. This was irrespective of carbohydrate complexity or level in the diet. However, simple sugars might suppress the appetite of trout in the longer term. The biochemical status of liver via plasma glucose concentration may play a more important role compared to gastric fullness in the long- term regulation of appetite. It was postulated that X-radiography was a paramount technique for the quantification of sequential meals and return of appetite measurements in these investigations. The above parameters and their interactions were studied in relation to the physiological control of feed intake in order to develop a more defined model for such processes and to improve the optimum feeding regimes for rainbow trout under intensive production conditions. This is discussed within the wider concept of fish nutrition, and the implications for future research in this area are stated.
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Hague, Mark. "Ice - ocean - atmosphere interactions in the Southern Ocean and implications for phytoplankton phenology." Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33708.
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The annual advance and retreat of sea ice in the Southern Ocean is recognised as one of the largest seasonal events on Earth. Such considerable physical changes have profound effects on the vertical structure of the water column, and hence controls the availability of both light and nutrients to phytoplankton. This means that in the region seasonally covered by sea ice (the SSIZ), the timing of the growth and decline (phenology) of phytoplankton is determined to a large degree by the dynamic interactions between ice, ocean and atmosphere. However, this region is simultaneously one of the most poorly observed in the global ocean, and one of the most complex. This has led to significant gaps in our understanding of how sea ice modulates the exchanges of heat and momentum between atmosphere and ocean, as well as the implications this has for phytoplankton phenology in the SSIZ. This study seeks to address these gaps by combining both model and observationallybased methods. The lack of observational data are directly tackled through an analysis of BGC-Argo float data sampling under ice. Such data reveal high growth rates in the presence of near full ice cover and deep mixed layers, conditions previously thought to prevent growth. These results suggest a revision of our current understanding of the drivers of under ice phytoplankton phenology, which should take into account the unique character of Antarctic sea ice and its effect on the under ice light environment. In addition, results obtained from several numerical process studies indicates that phytoplankton may have a higher affinity for low light conditions than previously thought. From a modelling perspective, an analysis and intercomparison of 11 Earth System Models (ESMs) and their representation of vertical mixing and phenology is presented. This revealed that misrepresentations in phenology where driven by model biases in sea ice cover and vertical mixing. That is, only models with either too much or too little ice cover were able to simulate phenology close to observations. Furthermore, a strong correlation between the location of the ice edge and the extent of vertical mixing suggested that ESMs overly dampen ocean-atmosphere fluxes as mediated by sea ice. This led to the development of a regional ocean-sea ice model of the Atlantic sector of the Southern Ocean, from which experiments enhancing both heat and momentum fluxes could be conducted. It was found that the model responded more uniformly to enhanced heat flux, generally deepening the mixed layer closer to observations in winter. On the other hand, the effects of enhanced momentum flux (implemented by increased air-ice drag) where more complex and spatially heterogeneous, with contrasting responses depending on the initial vertical density structure of the water column. Overall, the argument is made that the unique features of Antarctic sea ice should be included in models if we are to improve the representation of the SSIZ mixed layer, and hence phenology