Dissertations / Theses on the topic 'Sulfinic acids'

Road construction through sulfidic materials in Virginia has resulted in localized acid rock drainage (ARD) that threatens water quality, fill stability, integrity of building materials, and vegetation management. The objectives of this study were: i) to develop a state-wide sulfide hazard rating map based on characterization of the geologic formations associated with acid roadcuts, ii) to estimate depth to sulfidic sediments in the Coastal Plain based on landscape relationships, and iii) to evaluate potential acidity testing procedures on diverse materials. Geologic formations associated with acid roadcuts were characterized by potential peroxide acidity (PPA) and S content, and grouped into four categories. Listed in order of increasing severity, these formations included: the Tabb Formation (Coastal Plain), the Lynchburg Group of the Ashe Formation (Blue Ridge), the Chesapeake Group and Lower Tertiary deposits (Coastal Plain), the Millboro shale, Marcellus shale, Chatanooga shale and Needmore Formation (Valley and Ridge), and the Quantico Formation (Piedmont). Evaluation of landscape parameters near Richmond, Virginia, indicated that the likelihood of encountering sulfidic materials within a given depth at a specific location was related to elevation and mapped soil types. Elevation and soil map units were assigned to risk classes to indicate the likelihood of encountering sulfides within a depth of 9 m. Comparison of PPA and S content for 296 diverse samples indicated that S may serve as a screening tool to evaluate materials without carbonates. Comparison of PPA and conventional Acid-Base Accounting (ABA) for 14 diverse samples indicated that PPA and ABA were highly correlated, with PPA yielding 0.60 to 0.95X the amount of acidity as ABA. Potential acidity by Soxhlet extraction and PPA were equivalent for 3 of 4 diverse samples. Average acidity and metal contents of leachate from Soxhlet extractors were correlated with acidity and metals of road drainage. Sulfide hazard analysis should be an essential step in the pre-design phase of highway construction and other earth-disturbing activities.
Ph. D.

Les peroxyrédoxines (Prx) sont des peroxydases à thiol, ubiquitaires, qui jouent un rôle central dans la physiologie du peroxyde d’hydrogène. Une famille de Prx dite "2-Cys-Prx typique" possède une propriété unique de suroxydation de la Cys catalytique sous forme acide sulfinique, qui constitue un mécanisme de régulation des fonctions des 2-Cys-Prx typiques en tant que peroxydase, capteur de peroxyde ou protéine chaperon. La réduction des 2-Cys-Prx typiques suroxydées est catalysée par la Sulfirédoxine (Srx), une sulfinyl réductase ATP-dépendante dont la constante catalytique est de l’ordre de 1-2 min-1, une valeur faible qui doit être corrélée au rôle de Srx dans la régulation redox. L’objectif de ce travail était d’analyser l’enzymologie de la régulation du système Prx/Srx au niveau, du processus de suroxydation des 2-Cys-Prx typiques, de l’étape limitante de la Srx, et de son recyclage par les systèmes redox cellulaires. Dans un premier temps, nous avons caractérisé les deux étapes du cycle catalytique de la 2-Cys-Prx typique majeure de S. cerevisiae Tsa1, dont la compétition contrôle la sensibilité à la suroxydation, par une stratégie combinant cinétiques rapides, système enzymatique couplé et modélisation cinétique. Ces travaux suggèrent que cette compétition est contrôlée par une réorganisation conformationnelle au cours du cycle catalytique de la Tsa1. Dans un second temps, l’étude de la première étape du mécanisme catalytique de Srx, qui consiste en l’activation ATP-dépendante du groupement acide sulfinique de la 2 Cys-Prx a permis, i) de montrer que l’étape limitante de la réaction catalysée par Srx était associée au processus chimique de transfert de phosphate, et ii) de proposer un modèle d’assemblage du complexe Michaelien Prx/Srx/ATP formé lors de ce processus. Enfin, par une approche combinant cinétiques enzymatiques in vitro et génétique de la levure in vivo, nous avons établi que le mécanisme de recyclage des Srx à 1 Cys existant chez les plantes ou les mammifères implique le rôle du glutathion comme réducteur cellulaire, contrairement à la Srx de S. cerevisiae qui est recyclée par le système thiorédoxine. De façon inattendue, la spécificité du glutathion dans ce mécanisme est assurée par un événement de reconnaissance au sein du complexe Prx/Srx
The peroxiredoxins (Prx) are ubiquitous thiol peroxidases, which play a central role in the physiology of hydrogen peroxide. A subclass of Prx called "typical 2-Cys-Prx" has a unique property to hyperoxidize the catalytic Cys into the sulfinic acid form, which acts as a regulation mechanism of their functions, as peroxidase, peroxide sensor or protein chaperone. The reduction of the overoxidized form is catalyzed by sulfiredoxin (Srx), an ATP-dependent sulfinyl reductase whose catalytic constant is about 1-2 min-1, a low value that must be correlated to the role of Srx in redox regulation. The aim of this study was to analyze the enzymology of the regulation of the Prx/Srx system at three diffrents points of control: the hyper-oxidation process of typical 2-Cys-Prx, the rate-limiting step of the Srx mechanism and the recycling step of Srx by the cellular thiol redox systems. We have first characterized the competition mechanism between the two steps of the catalytic mechanism of the major typical 2-Cys-Prx of S. cerevisiae, Tsa1, through a strategy combining rapid kinetics, coupled enzyme system and kinetic modelling analysis. This work suggests that the sensitivity to hyper-oxidation is controlled by a conformational reorganization during the catalytic cycle of Tsa1. Next, the study of the first step of Srx catalytic mechanism, which involves the ATP-dependent activation of the sulfinic acid form of typical 2-Cys Prx i) has shown that the rate-limiting step is associated with the chemical phosphate transfer process, and ii) provided an assembly model of the Michaelien complex Prx/Srx/ATP, formed during this process. Finally, through the combination of in vitro enzyme kinetics and in vivo yeast genetic tools, we established that the recycling mechanism of one Cys Srx, existing in plants or mammals, involves the glutathione (GSH) as reducer in cells, contrary to the Srx from S. cerevisiae, which is recycled by the Thioredoxin system. Unexpectedly, our study suggests that GSH binds the thiolsulfinate complex, confirming the role of GSH as the primary reducing system of 1-Cys-Srx

La suroxydation des peroxyrédoxines (Prx) est un mécanisme post-traductionnel essentiel impliqué dans la régulation et la signalisation cellulaire redox. Les Prx sont des peroxydases à thiol, qui réagissent avec les peroxydes pour former un intermédiaire acide sulfénique. Leur sensibilité à la suroxydation dépend de la compétition entre la réaction de sulfinylation et la formation d’un pont disulfure au cours du cycle peroxydase. Cette compétition est contrôlée par une transition conformationnelle entre deux conformations FF : structurée et LU : localement déstructurée. Dans ce projet, nous abordons le mécanisme de suroxydation de Tsa1, la principale Prx1 cytosolique de S. cerevisiae, par des analyses cinétiques à l'état pré-stationnaire en cinétique rapide, à l'état stationnaire et in vivo. Une phase cinétique correspondant à un changement de conformation associé à la transition FF/LU a été identifiée, montrant que la formation de l’acide sulfénique facilite cette transition. L’utilisation de mutants de sensibilité à la suroxydation altérée et de différents substrats peroxydes a permis de montrer que la sensibilité est découplée de l'étape de formation du pont disulfure et ne dépend que des constantes de vitesse de sulfinylation et de transition conformationnelle FF/LU. A partir de ces deux paramètres, nous pouvons prédire l'indice de sensibilité à la suroxydation CHyp1%, une prédiction démontrée in vitro et in vivo
Peroxiredoxins from the Prx1 subfamily (Prx) are moonlighting peroxidases that operate in peroxide signaling and are regulated by sulfinylation. Prxs offer a major model of protein−thiol oxidative modification. They react with H2O2 to form a sulfenic acid intermediate that either engages into a disulfide bond, committing the enzyme into its peroxidase cycle, or again reacts with peroxide to produce a sulfinic acid that inactivates the enzyme. Sensitivity to sulfinylation depends on the kinetics of these two competing reactions and is critically influenced by a structural transition from a fully folded (FF) to locally unfolded (LU) conformation. Analysis of the reaction of the Tsa1 Saccharomyces cerevisiae Prx with H2O2 by Trp fluorescence-based rapid kinetics revealed a process linked to the FF/LU transition that is kinetically distinct from disulfide formation and suggested that sulfenate formation facilitates local unfolding. Use of mutants of distinctive sensitivities and of different peroxide substrates showed that sulfinylation sensitivity is not coupled to the resolving step kinetics but depends only on the sulfenic acid oxidation and FF-to-LU transition rate constants. From these two parameters, the relative sensitivities of Prxs toward hyperoxidation with different substrates can be predicted, as confirmed by in vitro and in vivo patterns

In insects, the cuticle provides protection against physical injury and water loss, rigidness for muscle attachment and mechanical support, and flexibility in inter-segmental and joint areas for mobility. As most insects undergo metamorphosis, they need to shred off old cuticle and synthesize new cuticle to fit the body shape and size throughout their life cycles. The newly formed cuticle, mainly composed of cuticular proteins, chitin, and sclerotizing reagents, needs to be hardened through the crosslinks between cuticular proteins and sclerotizing reagents. This dissertation concerns the biochemical activities of several pyridoxal 5-phosphate (PLP)-dependent decarboxylases with most of them involved in insect cuticle hardening. Herein, we first present a detailed overview of topics in reactions and enzymes involved in insect cuticle hardening. Aspartate 1-decarboxylase (ADC) is at the center of this dissertation. beta-alanine, the product of ADC-catalyzed reaction from aspartate, is the component of an important sclerotizing reagent, N-beta-alanyldopamine; the levels of beta-alanine in insects regulate the concentrations of dopamine, therefore affecting insect sclerotization and tanning (collectively referred as cuticle hardening in this dissertation).

Biochemical characterization of insect ADC has revealed that this enzyme has typical mammalian cysteine sulfinic acid decarboxylase (CSADC) activity, able to generate hypotaurine and taurine. The result throws lights on research in the physiological roles of insect ADC and the pathway of insect taurine biosynthesis. Cysteine was found to be  an inactivator of several PLP-dependent decarboxylases, such as ADC, glutamate decarboxylase (GAD) and CSADC. This study helps to understand symptoms associated with the abnormal cysteine concentrations in several neurodegenerative diseases. A mammalian enzyme, glutamate decarboxylase like-1 (GADL1), has been shown to have the same substrate usage as insect ADC does, potentially contributing to the biosynthesis of taurine and/or beta-alanine in mammalian species. Finally, the metabolic engineering work of L-3, 4-dihydroxyphenylalanine decarboxylase (DDC) and 3, 4-dihydroxylphenylacetaldehyde (DHPAA) synthase has revealed that the reactions of these enzymes could be determined by a few conserved residues at their active site. As both enzymes have been implicated in the biosynthesis of sclerotizing reagents, it is of great scientific and practical importance to understand the similarity and difference in their reaction mechanisms. The results of this dissertation provide valuable biochemical information of ADC, DDC, DHPAA synthase, and GADL1, all of which are PLP-dependent decarboxylases. ADC, DDC, DHPAA synthase are important enzymes in insect cuticle hardening by contributing to the biosynthesis of sclerotizing reagents. Knowledge towards understanding of these enzymes will promote the comprehension of insect cuticle hardening and help scientists to search for ideal insecticide targets. The characterization of GADL1 lays groundwork for future research of its potential role in taurine and beta-alanine metabolism.

Ph. D.

Les peroxyrédoxines à deux cystéines typiques (2-Cys Prx) sont impliquées dans la résistance des cellules au stress oxydant associé à H2O2, en réduisant H2O2 en H2O. En parallèle, ces enzymes participent à la transduction du signal dépendant de H2O2 en tant que second messager, via leur état rédox. La suroxydation sous forme d’acide sulfinique des 2-Cys Prx typiques eucaryotes est une modification posttraductionnelle qui inactive l’activité peroxydase, permettant de réguler le passage du message cellulaire H2O2-dépendant. La réduction de cette espèce oxydée est essentielle pour la viabilité des cellules. Cette réaction est catalysée par les sulfirédoxines (Srx). Les études réalisées ont permis de caractériser le mécanisme catalytique de Srx de S. cerevisiae qui consiste en : 1) l’activation de la fonction acide sulfinique sous forme d’anhydride phosphoryl sulfinique, par transfert direct du phosphate ? de l’ATP ; 2) la réduction de la fonction acide sulfinique activée par attaque de la Cys catalytique de Srx, ce qui conduit à un intermédiaire covalent thiosulfinate Prx/Srx ; 3) le recyclage de Srx avec la libération de PrxSOH. Au niveau du recyclage de l’activité Srx, deux classes de Srx peuvent être définies, celle à deux Cys et celle à une Cys. La classe de Srx à deux Cys, composée jusqu’à présent de Srx de levures, possède une Cys de recyclage qui attaque le thiosulfinate au niveau de la Cys de Srx, libérant la PrxSOH et la Srx oxydée sous forme de pont disulfure intramoléculaire. Cette forme oxydée de Srx est ensuite reconnue et réduite par la thiorédoxine. La classe de Srx à une Cys dont font partie les Srx de mammifères, ne possédant pas de Cys de recyclage, passe par un mécanisme de recyclage impliquant un réducteur autre que la Trx, qui reduit directement la fonction thiosulfinate, et dont la nature reste à déterminer
Typical two-cysteine peroxiredoxines are involved in cell resistance against H2O2-induced oxidative stress, by reducing H2O2 in H2O. Furthermore, these enzymes take part in H2O2 signalling, which is transmitted and regulated by their redox state. The eukaryotic typical 2-Cys Prxs are subject to post-translational modification under sulfinic acid oxidation state, which inactivates have lost their peroxidase activity and thus regulates allows the passage of H2O2-dependent cellular message. Reduction of the sulfinic acid oxidation state is essential for the cell viability. Sulfiredoxin (Srx) catalyzes this reduction. These research studies demonstrated that the catalytic mechanism of Srx occurs in three steps: first, the sulfinic acid is activated as a sulfinyl phosphoryl anhydride intermediate by a direct transfer of the ?-phosphate of ATP; second, the activated sulfinic acid intermediate is reduced via attack of the catalytic Cys of Srx, which leads to formation of a thiosulfinate intermediate and; third Srx, is recycled with concomitant release of the PrxSOH product of the reaction. Two classes of Srx could be defined depending on the mechanism of Srx recycling. The class comprising yeast Srxs have one recycling Cys. This Cys attacks the thiosulfinate intermediate, resulting in PrxSOH release and formation of an oxidized Srx intermediate. This oxidized species, with an intramolecular disulfide bond, is recognized and reduced by thioredoxin. In the class comprising Srx devoid of recycling Cys, which includes the mammalian Srxs, Srx is recycled by a reducer distinct from thioredoxin, which reduces directly the thiosulfinate function

Deux nouvelles méthodes de dégradations de la chaîne latérale des acides biliaires ont été élaborées. La première approche met en jeu une nouvelle voie de synthèse des Δ² -oxazolines ainsi que leur utilisation pour l'introduction d'une insaturation en position 22(23) sur la chaine latérale des acides biliaires. La généralité de ces deux réactions a été examinée. La deuxième voie est fondée sur une nouvelle synthèse des 23-céto esters à partir des acides biliaires. L'auto-oxydation de ces esters permet ensuite de dégrader la chaîne latérale. Un mécanisme pour cette dernière transformation a été proposé
Two new methods for the degradation of the side chain of bile acids have been elaborated. The first method involves a new synthetic pathway to Δ² -oxazolines and their use for the introduction of a double bond between carbon atoms 22 and 23. The general applicability to these two reactions has been examined. The second method is based on a novel synthesis of 23-keto esters derived from bile acids. Autoxidation of these esters leads ta subsequent side chain degradation. A mechanism for this degradation is proposed

La synthèse des N-sulfonyl, des N-sulfinyl et des N-sulfénylimines a été réalisée. Ces imines N-sulfurées ont été testées dans la réaction de Staudinger sur des cétènes [alpha]-oxygénés. Cette réaction de cycloaddition [2+2] a été appliquée avec succès à de nombreuses imines N-sulfénylées pour donner des N-sulfényl β-lactames avec de bons rendements et de bonnes sélectivités. Ces azétidinones porteuses d'un groupement électrodonneur sur l'atome d'azote du cycle ont ensuite été engagées dans des réactions d'oxydation de l'atome de soufre pour donner de façon quantitative les produits N-sulfinylés et N-sulfonylés. Ces nouveaux β-lactames, porteurs de groupements électroattracteurs sur l'atome d'azote, ont été utilisés dans des réactions d'ouverture nucléophile avec des amines, des alcools ou des thiols pour donner de nouveaux β-aminoacides [alpha]-oxygénés
The synthesis of N-sulfonyl, N-sulfinyl and N-sulfenylimines has been achieved. These N-thiolated imines were tested in the Staudinger reaction with [alpha]-oxygenated ketenes. The [2+2] cycloaddition reaction was successfully applied to many N-sulfenylimines to give N-sulfenyl β-lactames with good yields and a good selectivity. These azetidinones bearing an electron-donor group on the nitrogen of the cycle were then used in the oxidation reaction of the sulphur to give the N-sulfinylated and N-sulfonylated cycloadducts. The new β-lactames bearing an electron-acceptor group on the nitrogen were used in nucleophilic ring opening reactions with amines, alcohols or thiols to give new [alpha]-oxygenated β-aminoacids

Palladium complexes have the ability to catalyse cross-coupling of two organic moieties through the formation of transient metal-carbon bonds, thus bringing them closer to each other to facilitate the formation of a new bond. Palladium-catalysed coupling reactions are one of the most important carbon-carbon forming reactions available to organic chemists and many of these reactions rely on the reactivity of aryl-palladium complexes. The investigation of new aryl-palladium precursors is thus of great interest, especially as more sustainable and economic methods can be developed. This thesis describes the use of carboxylic acids and sodium arylsulfinates as such new arylating agents. Protocols for microwave-assisted palladium(II)-catalysed decarboxylative synthesis of electron-rich styrenes and 1,1-diarylethenes were developed. However, these transformations had very limited substrate scopes which prompted the investigation of sodium arylsulfinates as alternative arylating agents. These substrates were employed in the microwave-assisted palladium(II)-catalysed desulfitative addition to nitriles, and the substrate scope was demonstrated by combining a wide array of sodium arylsulfinates and nitriles to yield the corresponding aryl ketones. The application of the desulfitative reaction in a continuous flow setup was demonstrated, and aluminium oxide was identified as safe alternative to borosilicate glass as a reactor material. The mechanisms of the decarboxylative and desulfitative transformations were investigated by density functional theory (DFT) calculations. The desulfitative reaction was also investigated by direct electrospray ionization mass spectrometry (ESI-MS), providing further mechanistic insight. Finally, a protocol for the safe and convenient synthesis of a wide range of sodium arylsulfinates was developed.

Systemic lupus erythematosus (SLE) is the prototypic systemic autoimmune disease, whereas autoimmune polyendocrine syndrome type 1 (APS1) is a rare autosomal disorder characterized by combinations of organ-specific autoimmune manifestations including hypoparathyroidism and intestinal dysfunction, and may serve as a model for organ-specific autoimmunity. Autoantibodies directed against proteins expressed in the affected tissues are found in both diseases. From a chondrocyte cDNA expression library, we identified the protein AHNAK as an autoantigen in SLE. Anti-AHNAK antibodies were found in 29.5% (18/61) of patients with SLE, 4.6% (5/109) of patients with rheumatoid arthritis, and 1.2% (2/172) of blood donors. Using a candidate approach, we analyzed the prevalence in APS1 and other organ-specific autoimmune diseases, of autoantibodies against the pyridoxal phosphate-dependent enzymes histidine decarboxylase (HDC) and cysteine sulfinic acid decarboxylase (CSAD), which are structurally closely related to known autoantigens. Anti-HDC and anti-CSAD reactivity was detected exclusively in APS1 patient sera. Anti-HDC antibodies were detected in 37.1% (36/97) of the APS1 sera, did not cross-react with aromatic L-amino acid decarboxylase, and were associated with intestinal dysfunction and loss of histamine-producing gastric enterochromaffin-like cells. In contrast, anti-CSAD reactivity was detected in 3.6% (3/83) of APS1 sera and cross-reacted with recombinant glutamic acid decarboxylase. From a parathyroid cDNA expression library, novel spliced transcripts of the CLLD4 gene on human chromosome 13q14, encoding 26 and 31 kDa isoforms recognized by autoantibodies in 3.4% (3/87) of APS1 patients, were identified and found to be preferentially expressed in lung and ovary. Both isoforms contain an N-terminal BTB/POZ domain, similarly to the TNF-alpha-regulated protein B12, localize both to the cytoplasm and nucleus in transfected COS cells, and form oligomers in vitro. The CLLD4 gene is located in a region frequently deleted in several forms of cancer, including lung and ovarian tumors. In conclusion, we have identified and partially characterized AHNAK and HDC as two common targets of autoantibodies in SLE and APS1, respectively. We have also identified CSAD and CLLD4 as two minor autoantigens in APS1, one of which is a novel protein with unknown function.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1990.
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碩士
國立臺灣大學
動物科學技術學研究所
99
Cysteine sulfinic acid decarboxylase (CSAD; EC 4.1.1.29) is the rate-limiting enzyme in the biosynthesis of taurine, 2-aminoethane sulfonic acid. CSAD is also named sulfinoalanine decarboxylase and cysteine-sulfinate decarboxylase, and has been cloned and characterized in liver of rat and mice. Taurine can be found abundantly in blood cells, muscles and brain of vertebrates and its biosynthesis was detected in various extrahepatic tissues. There are numbers of positive effects of taurine on physiological processes such as bile salt synthesis, osmoregulation, lipid metabolism and oxidative stress inhibition. Taurine is also critical for normal embryonic development, but its exact role in embryogenesis remains to be elucidated. The acquisition of taurine in embryos depends on de novo synthesis and placental/yolk transfer. Knockdown of taurine transporter induced only slightly increased apoptosis in central nervous system during zebrafish development. It implies that de novo synthesis may play a more dominant role during zebrafish embryogenesis. To investigate the roles of de novo synthesis of taurine during embryonic development, zebrafish CSAD (zCSAD) was cloned and the cDNA encodes for a protein of 482 amino acids with its sequence highly homologous to mammalian CSAD and conserved throughout evolution. The zCSAD was only detected in the cell lysate but not in the medium of HEK293T cells transiently transfected by zCSAD, suggesting that zCSAD is not a secreted protein. Semi-quantitative RT-PCR detected zCSAD mRNA as early as 0 hour post fertilization (hpf) indicating the existence of maternal zCSAD message. Whole-mount in situ hybridization demonstrated that zCSAD was expressed in yolk syncytial layer and various mesoderm tissues such as pronephric duct, notochord and cardiogenic field during early embryogenesis. Knockdown of zCSAD by morpholino oligos (MOs) reduced taurine level in embryos and increased early mortality, elevated cell death in cardiogenic region and tail, pericardial edema and malformation of tail. Coinjecting zCSAD MOs and mRNA could partially rescue the cardiac phenotypes, indicating that zCSAD is important for heart development. On the other hand, when embryos were incubated in 13 mM taurine supplement buffer after injecting MOs, taurine treatment could diminish the mortality and cardiac phenotypes at 72 hpf, suggesting that the heart malformation caused by zCSAD knockdown was due to taurine deficiency. To further investigate the molecular mechanism by which taurine regulates these phenotypes, real-time PCR was performed to detect mRNA expression of heart formation marker (NK2 transcription factor related 5, Nkx2.5), hematopoiesis markers (runt-related transcription factor 1, runx1; kinase insert domain receptor like, KDRL), apoptosis markers (BCL2-antagonist of cell death; caspase 3) and unfolded protein response regulator genes (activating transcription factor 6, ATF6; X-box binding protein-1 spliced form, XBP-1S) in zCSAD knockdown embryos and the results showed a trend of numerical increase without significance. In conclusion, knockdown of zCSAD reduced taurine biosynthesis in zebrafish embryos and resulted in increasing cell death and malformations of heart. These findings indicated that taurine de novo synthesis via CSAD plays an important role in cardiac development and as a cell survival factor in zebrafish embryos.

Acid sulfate soils (ASS) are soils or sediments that contain sulfuric, hypersulfidic or hyposulfidic materials or are affected by transformation of sulfidic minerals (e.g., pyritic, FeS2). ASS are widely distributed globally and typical in environments such as coastal and inland wetlands. The main biogeochemical processes influencing the pH in ASS are sulfate reduction and pyrite oxidation. Under flooded conditions (low redox potential), sulfate reducing bacteria (SRB) using easily decomposable organic matter (OM) as their energy source, produce sulfide, which reacts with iron in sediments to form pyrite or mono-sulfides, which are stable under flooded conditions. Sulfate reduction consumes protons and therefore, results in a pH increase. When sulfidic sediments dry, pyrite can oxidise and generates acidity. In soils with low pH buffer capacity (pHBC), this can result in severe acidification and metal solubilisation. Often sulfate reduction does not occur even after pro-longed flooding which may be due to lack of organic carbon (C) availability. Management strategies aiming to ameliorate ASS include liming or inundation. However, they may be uneconomical, unsustainable or can be ineffective. Therefore, alternative strategies are required to manage ASS. OM addition could be an effective strategy to ameliorate ASS due to its role during sulfate reduction. It may also maintain higher level of pH even during dry periods by buffering the acid generated and stimulating microbial activity and thus oxygen consumption through. Readily degradable C of OM and duration, in which OM remain available to sulfate reducing bacteria, may be important in maintaining wetland ASS. Management of wetlands often involves introduction of wet and dry periods to restore ecosystem health. OM addition could be included to improve the effectiveness of this strategy. In this thesis, soils from Banrock station wetland were used in a series of incubation experiments. The wetland has extensive ASS and acidification was observed in many areas in a survey conducted in 2009. Since then, wetland managers have introduced wet-dry cycles to improve wetland health. The aim of this thesis was to determine the effect of type of organic C or sulfidic clay soils added on pH and redox potential (Eh) in ASS during wet and dry periods. The hypotheses to be tested were: (¡) Addition of easily decomposable OM will have a greater effect on pH and redox potential than poorly decomposable OM (¡¡) Acidification during the dry period will be smaller at high compared to low water content because high water content limits diffusion of oxygen (¡¡¡) Mixing sulfidic clay soils into ASS will minimise pH changes during wet and dry periods, particularly clay soils with high pH buffer capacity. In the first experiment, the effect of type of organic amendment was investigated. Three wetland ASS (sulfuric, hypersulfidic and hyposulfidic) collected from different depths were used. The soils, unamended or amended with 10 g C kg-1 as glucose, wheat straw, pea straw or Phragmites litter, were incubated for 18 weeks under flooded conditions (“wet period”) followed by 10 weeks during which the soils were maintained at 100% of maximum water-holding capacity (WHC) (“dry period”). During the wet period, the pH decreased in the control and with glucose to pH 3-4, but increased or was maintained in residueamended soils (pH at the end of the wet period about 7). In the dry period, the pH of the control and glucose amended soils remained low, whereas the pH in residue amended soils decreased. However, at end of the dry period, the pH was higher in residue amended soils than in the control or glucose amended soils, particularly with pea straw (carbon: nitrogen 50, C/N 50). It can be concluded that amendment of ASS with plant residues (particularly those with low to moderate C/N ratio) can stimulate pH increase during flooding and reduce acidification under oxidizing conditions. The second experiment was carried out to assess the effect of OM addition on pH in a wet-dry cycle followed by a second wet period. A further aim was to investigate the influence of water content during the dry period on acidification. Three ASS (sulfuric, hypersulfidic and hyposulfidic) were collected from one profile and unamended or amended with 10 g C kg-1 as finely ground wheat straw. The soils were exposed to a submerged (wet) period, a dry period, followed by another wet period. In the first wet period (10 weeks), the pH increased only in the amended soils, which was accompanied by a strong decrease in Eh. To investigate the effect of water content during the dry period on pH, the soils were rapidly dried to 40, 60, 80 or 100% of WHC at the start of the dry period. This water content was maintained during the dry period. The pH decrease during the 10-week dry period was greater in amended than in unamended soils and greater at 60, 80 or 100% than at 40% of WHC. At the end of the dry period, the pH was higher in amended than in unamended soils and higher at 40% of WHC than at the higher water contents. In the second wet period (16 weeks), the pH increased only in the amended soils. The pH increase was accompanied by a decrease in Eh in the amended soils. The water content in the previous dry period did not influence pH in the second wet period in the unamended soils, but in the amended soils, the pH was higher in soils previously maintained at 40% of WHC than that maintained at higher water contents. At the end of the second wet period, the pH was higher in amended than in unamended soils. This study shows the ameliorative effect of OM addition in ASS. OM addition can improve energy supply for sulfate reducers which results in an increase in pH during the wet period and lead to a higher pH in the oxidation period. The smaller pH increase and Eh decrease in amended soils in the second compared to the first wet period suggests that OM decomposition was lower in the second wet period likely because rapidly decomposable compounds had been utilised in the previous wet and dry periods and only recalcitrant OM remained. Therefore OM may have to be added repeatedly for sustained amelioration of ASS. The aim of the third experiment was to investigate the effect of addition of hyposulfidic clay soils to a sufuric sandy soil on pH changes in reduced and oxidised conditions. A sulfuric sandy soil (pH 4.1) was mixed with three hyposulfidic clay soils (with clay contents ranging between 38 and 72%) to give clay soil proportions of 0, 25, 50, 75 and 100 (% dry soil). According to their net negative acidity, the three clay soils are referred to as: NA-334, NA-54 and NA-8 (values in moles H+ tonne-). The soils were amended with wheat straw at 10 g of C kg -1 and then incubated for 14 weeks under reducing conditions (wet period) followed by 11 weeks incubation under oxidising conditions (dry period) during which they were maintained at 100% of maximum WHC. The pH of the sulfuric soil alone increased during the wet period by about two pH units (to pH 6) and decreased by more than two pH units (to pH <4) during the dry period. In the clay soils alone and treatments with sulfuric soil, the pH during the wet period decreased by 0.5 to 1 unit with NA-334 and NA-54 and increased by one unit with NA-8. The pH was >6 in all clay treatments at the end of the wet period. During the dry period, the pH remained above pH 7 with NA-334 and decreased by about one unit (to pH 5.5) with NA-8. In treatments with NA-54, the pH decrease during the dry period depended on the proportion of clay soil, ranging from 0.5 pH unit with 75% clay soil to two pH units with 25% clay soil. The capacity of the clay soil treatments to maintain stable pH during wet and dry periods depended mainly on the negative net acidity of the added clay soils, but was not related to their concentration of reduced inorganic sulfur or clay content. It can be concluded that addition of clay soils with high negative net acidity could be used to ameliorate acidity in ASS. The fourth experiment was conducted to determine the effect of OM addition over two successive wet-dry cycles in four ASS. Four soils differing in clay content (10, 15, 23, 38% referred to as C10, C15, C23 and C38) were unamended or amended with 10 g C kg-1 finely ground wheat straw and incubated over 24 weeks with each wet and each dry period lasting 6 weeks. Soil pH increased in both wet periods, particularly in amended soils with low clay content (C10 and C15). The Eh decreased more strongly in amended soils than in unamended soils and became negative from week 2 onwards whereas the Eh stayed positive in unamended soils except C38. In the dry periods, the pH decreased more strongly in amended soils than in unamended soils, particularly in C10 and C15. Changes in pH during wet and dry periods were greater in soils with low clay content (C10, C15) than those with high clay content (C23, C38). The effect of wheat straw addition on pH at the end of wet and dry periods did not differ between the two wet-dry periods, with a higher pH in amended than unamended soils. This study showed that wheat straw addition maintains its ameliorative effect on soil pH for at least two wet-dry cycles, but the pH effect depends on clay content, being greater in soils with low clay content. The effectiveness of this method would have to be tested under field conditions, particularly where wet and dry periods continue for longer periods.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2016.