Effects Of Oxygen Availability Research Articles

The Effects of Oxygen Availability in the Seed Container during Storage on Seed Germination in Tomato, Onion, Cabbage, and Marrow Seeds

This research was conducted to test the effect of oxygen content (low O2, high O2, air) during hermetic seed storage at 20±2°C over 8 and 12 months on seed germination and seedling root and shoot length in tomato, onion, cabbage, and marrow seeds. Samples with low oxygen storage had higher seed germination as well as longer root and shoot lengths than both control and high oxygen storage. When the storage period extended from 8 to 12 months, the germination percentages also reduced. However, these results varied among the species. The greatest advantage of low oxygen storage was obtained in tomatoes, which exhibited 15% and 9% higher germination compared to the control after 8 and 12 months of storage, respectively. The longest root and shoot lengths of 6.4 cm and 11.6 cm, respectively, were obtained from the low oxygen storage treatments. A similar positive effect of low oxygen storage was observed in onion and cabbage seeds but not in marrows. Results indicated that oxygen level in the packets during storage can be an effective component to maintain high seed germination and seedling growth potential (seed vigour). The difference in the effect on different species is a matter of further research.

Effects of oxygen availability on mycobenthic communities of marine coastal sediments

In coastal marine sediments, oxygen availability varies greatly, and anoxic conditions can develop quickly over low spatial resolution. Although benthic fungi are important players in the marine carbon cycle, little is known about their adaptation to fluctuating availability of oxygen as terminal electron acceptor. Here, we study which part of a mycobenthic community from oxic coastal sediments can thrive under temporarily anoxic conditions. We test whether phylogeny or certain fungal traits promote plasticity in respect to changes in oxygen availability. Therefore, we incubated mycobenthos under oxic and anoxic conditions, performed ITS2 Illumina tag-sequencing and an additional meta-analysis on a literature survey. Half of all OTUs showed a plasticity towards changing oxygen availability and exhibited different strategies towards anoxic conditions, with rapid response within hours or a delayed one after several days. The strategy of dimorphism and facultative yeasts were significantly linked to OTU occurrence in anoxic conditions, while phylogeny and other traits had less effect. Our results suggest that different fungal niches are formed over the duration of prolonged anoxic conditions. The taxon-specific proliferation seems to be regulated by the fine-tuning of various traits and factors. It is essential to take these results into account when conducting conceptual work on the functionality of the marine benthos.

Regulation of soil organic matter decomposition in permafrost-affected Siberian tundra soils - Impact of oxygen availability, freezing and thawing, temperature, and labile organic matter

The large amounts of soil organic matter (SOM) in permafrost-affected soils are prone to increased microbial decomposition in a warming climate. The environmental parameters regulating the production of carbon dioxide (CO2) and methane (CH4), however, are insufficiently understood to confidently predict the feedback of thawing permafrost to global warming. Therefore, the effects of oxygen availability, freezing and thawing, temperature, and labile organic matter (OM) additions on greenhouse gas production were studied in northeast Siberian polygonal tundra soils, including the seasonally thawed active layer and upper perennially frozen permafrost. Soils were incubated at constant temperatures of 1 °C, 4 °C, or 8 °C for up to 150 days. CO2 production in surface layers was three times higher than in the deeper soil. Under anaerobic conditions, SOM decomposition was 2–6 times lower than under aerobic conditions and more CO2 than CH4 was produced. CH4 contributed less than 2% to anaerobic decomposition in thawed permafrost but more than 20% in the active layer. A freeze-thaw cycle caused a short-lived pulse of CO2 production directly after re-thawing. Q10 values, calculated via the equal-carbon method, increased with soil depth from 3.4 ± 1.6 in surface layers to 6.1 ± 2.8 in the permafrost. The addition of plant-derived labile OM (13C-labelled Carex aquatilis leaves) resulted in an increase in SOM decomposition only in permafrost (positive priming). The current results indicate that the decomposition of permafrost SOM will be more strongly influenced by rising temperatures and the availability of labile OM than active layer material. The obtained data can be used to inform process-based models to improve simulations of greenhouse gas production potentials from thawing permafrost landscapes.

Field and laboratory studies reveal interacting effects of stream oxygenation and warming on aquatic ectotherms.

Aquatic ecological responses to climatic warming are complicated by interactions between thermal effects and other environmental stressors such as organic pollution and hypoxia. Laboratory experiments have demonstrated how oxygen limitation can set heat tolerance for some aquatic ectotherms, but only at unrealistic lethal temperatures and without field data to assess whether oxygen shortages might also underlie sublethal warming effects. Here, we test whether oxygen availability affects both lethal and nonlethal impacts of warming on two widespread Eurasian mayflies, Ephemera danica, Müller 1764 and Serratella ignita (Poda 1761). Mayfly nymphs are often a dominant component of the invertebrate assemblage in streams, and play a vital role in aquatic and riparian food webs. In the laboratory, lethal impacts of warming were assessed under three oxygen conditions. In the field, effects of oxygen availability on nonlethal impacts of warming were assessed from mayfly occurrence in 42 293 UK stream samples where water temperature and biochemical oxygen demand were measured. Oxygen limitation affected both lethal and sublethal impacts of warming in each species. Hypoxia lowered lethal limits by 5.5 °C (±2.13) and 8.2 °C (±0.62) for E. danica and S. ignita respectively. Field data confirmed the importance of oxygen limitation in warmer waters; poor oxygenation drastically reduced site occupancy, and reductions were especially pronounced under warm water conditions. Consequently, poor oxygenation lowered optimal stream temperatures for both species. The broad concordance shown here between laboratory results and extensive field data suggests that oxygen limitation not only impairs survival at thermal extremes but also restricts species abundance in the field at temperatures well below upper lethal limits. Stream oxygenation could thus control the vulnerability of aquatic ectotherms to global warming. Improving water oxygenation and reducing pollution can provide key facets of climate change adaptation for running waters.

Insulin- and warts-dependent regulation of tracheal plasticity modulates systemic larval growth during hypoxia in Drosophila melanogaster.

Adaptation to dynamic environmental cues during organismal development requires coordination of tissue growth with available resources. More specifically, the effects of oxygen availability on body size have been well-documented, but the mechanisms through which hypoxia restricts systemic growth have not been fully elucidated. Here, we characterize the larval growth and metabolic defects in Drosophila that result from hypoxia. Hypoxic conditions reduced fat body opacity and increased lipid droplet accumulation in this tissue, without eliciting lipid aggregation in hepatocyte-like cells called oenocytes. Additionally, hypoxia increased the retention of Dilp2 in the insulin-producing cells of the larval brain, associated with a reduction of insulin signaling in peripheral tissues. Overexpression of the wildtype form of the insulin receptor ubiquitously and in the larval trachea rendered larvae resistant to hypoxia-induced growth restriction. Furthermore, Warts downregulation in the trachea was similar to increased insulin receptor signaling during oxygen deprivation, which both rescued hypoxia-induced growth restriction, inhibition of tracheal molting, and developmental delay. Insulin signaling and loss of Warts function increased tracheal growth and augmented tracheal plasticity under hypoxic conditions, enhancing oxygen delivery during periods of oxygen deprivation. Our findings demonstrate a mechanism that coordinates oxygen availability with systemic growth in which hypoxia-induced reduction of insulin receptor signaling decreases plasticity of the larval trachea that is required for the maintenance of systemic growth during times of limiting oxygen availability.

Effects of oxygen availability on the combustion behaviour of materials in a controlled atmosphere cone calorimeter

The reaction-to-fire of materials is commonly studied with bench scale experiments conducted under controlled test conditions. Two bench-scale instruments commonly used for this purpose are the cone calorimeter and the fire propagation apparatus. Research performed with these test apparatuses on the burning behaviour of polymeric materials has demonstrated the significant effect on the results of test variables such as pressure, irradiance, flow velocity, etc. In spite of the fairly large number of studies, little is known concerning the effect of oxygen vitiation and reduced ventilation on the burning behaviour of polymeric materials. Recent work in a controlled oxygen environment raises the question of interpretation and accuracy of the results. This paper reports the results of a study to evaluate the effect of oxygen vitiation and reduced ventilation on the burning behaviour of materials in a controlled atmosphere cone calorimeter. The study was performed on a typical thermoplastic material, i.e., a black poly(methyl)methacrylate. The dependence of the results on the experimental fire conditions is presented and discussed. The experiments show that the inlet airflow rate is a major factor to consider when studying the burning behaviour of polymeric materials in an enclosure. It strongly affects the available amount of oxygen that can react and may lead to a misinterpretation of the results when the effects of oxygen are studied.

Neurovascular Uncoupling under Mild Hypoxic Hypoxia: An EEG–fMRI Study in Rats

The effects of oxygen availability on neurovascular coupling were investigated using simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), in addition to the monitoring of physiological parameters, in 16 α-chloralose-anesthetized rats. Mild hypoxic hypoxia (oxygen saturation=83.6±12.1%) induced significant reductions in fMRI responses (P<0.05) to electrical stimulation in the forepaw, but EEG responses remained unchanged. In addition, the changes in oxygen saturation were linearly correlated with the changes in the fMRI responses. These data further emphasize the importance of oxygen availability, which may regulate neurovascular coupling via the oxygen-dependent enzymatic synthesis of messenger molecules.

Effects of oxygen availability on maximum aerobic performance inMus musculusselected for basal metabolic rate or aerobic capacity

Maximum aerobic metabolism cannot increase indefinitely in response to demands for ATP production and, therefore, must be constrained by one (or many) of the steps of the oxygen transport and utilization pathways. To elucidate those constraints we compared peak metabolic rate elicited by running (V(.)(O₂,run)) in hypoxia (14% O₂), normoxia (21% O₂) and hyperoxia (30% O₂) of laboratory mice divergently selected for low and high basal metabolic rate (L-BMR and H-BMR, respectively), mice selected for maximum metabolic rate elicited by swimming (V(.)(O₂,swim)) and mice from unselected lines. In all line types (V(.)(O₂,run)) was lowest in hypoxia, intermediate in normoxia and highest in hyperoxia, which suggests a 'central' limitation of oxygen uptake or delivery instead of a limit set by cellular oxidative capacity. However, the existence of a common central limitation is not in agreement with our earlier studies showing that selection on high V(.)(O₂,swim) (in contrast to selection on high BMR) resulted in considerably higher oxygen consumption during cold exposure in a He-O₂ atmosphere than V(.)(O₂,run). Likewise, between-line-type differences in heart mass and blood parameters are inconsistent with the notion of central limitation. Although responses of V(.)(O₂,run) to hypoxia were similar across different selection regimens, the selection lines showed contrasting responses under hyperoxic conditions. V(.)(O₂,run) in the H-BMR line type was highest, suggesting that selection on high BMR led to increased cellular oxidative capacity. Overall, between-line-type differences in the effect of the oxygen partial pressure on V(.)(O₂,run) and in the components of O₂ flux pathways are incompatible with the notion of symmorphosis. Our results suggest that constraints on V(.)(O₂,max) are context dependent and determined by interactions between the central and peripheral organs and tissues involved in O₂ delivery.

Effects of dissolved oxygen availability and culture biomass at induction upon the intracellular expression of monoamine oxidase by recombinant E. coli in fed batch bioprocesses

The effects of oxygen availability and induction culture biomass upon production of an industrially important monoamine oxidase (MAO) were investigated in fed-batch cultures of a recombinant E. coli. For each induction cell biomass 2 different oxygenation methods were used, aeration and oxygen enriched air. Induction at higher biomass levels increased the culture demand for oxygen, leading to fermentative metabolism and accumulation of high levels of acetate in the aerated cultures. Paradoxically, despite an almost eight fold increase in acetate accumulation to levels widely reported to be highly detrimental to protein production, when induction wet cell weight (WCW) rose from 100% to 137.5%, MAO specific activity in these aerated processes showed a 3 fold increase. By contrast, for oxygenated cultures induced at WCW's 100% and 137.5% specific activity levels were broadly similar, but fell rapidly after the maxima were reached. Induction at high biomass levels (WCW 175%) led to very low levels of specific MAO activity relative to induction at lower WCW's in both aerated and oxygenated cultures. Oxygen enrichment of these cultures was a useful strategy for boosting specific growth rates, but did not have positive effects upon specific enzyme activity. Based upon our findings, consideration of the amino acid composition of MAO and previous studies on related enzymes, we propose that this effect is due to oxidative damage to the MAO enzyme itself during these highly aerobic processes. Thus, the optimal process for MAO production is aerated, not oxygenated, and induced at moderate cell density, and clearly represents a compromise between oxygen supply effects on specific growth rate/induction cell density, acetate accumulation, and high specific MAO activity. This work shows that the negative effects of oxygen previously reported in free enzyme preparations, are not limited to these acellular environments but are also discernible in the sheltered environment of the cytosol of E. coli cells.

Subfossil chironomid assemblages in deep, stratified European lakes: relationships with temperature, trophic state and oxygen

Summary 1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes. 4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state. 5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log-transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Paijanne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.

High stability and fast recovery of expression of the TOL plasmid-carried toluene catabolism genes of Pseudomonas putida mt-2 under conditions of oxygen limitation and oscillation.

Pseudomonas putida mt-2 harbors the TOL plasmid (pWWO), which contains the genes encoding the enzymes necessary to degrade toluene aerobically. The xyl genes are clustered in the upper operon and encode the enzymes of the upper pathway that degrade toluene to benzoate, while the genes encoding the enzymes of the lower pathway (meta-cleavage pathway) that are necessary for the conversion of benzoate to tricarboxylic acid cycle intermediates, are encoded in a separate operon. In this study, the effects of oxygen availability and oscillation on the expression of catabolic genes for enzymes involved in toluene degradation were studied by using P. putida mt-2 as model bacterium. Quantitative reverse transcription-PCR was used to detect and quantify the expression of the catabolic genes xylM (a key gene of the upper pathway) and xylE (a key gene of the lower pathway) in cultures of P. putida mt-2 that were grown with toluene as a carbon source. Toluene degradation was shown to have a direct dependency on oxygen concentration, where gene expression of xylM and xylE decreased due to oxygen depletion during degradation. Under oscillating oxygen concentrations, P. putida mt-2 induced or downregulated xylM and xylE genes according to the O₂ availability in the media. During anoxic periods, P. putida mt-2 decreased the expression of xylM and xylE genes, while the expression of both xylM and xylE genes was immediately increased after oxygen became available again in the medium. These results suggest that oxygen is not only necessary as a cosubstrate for enzyme activity during the degradation of toluene but also that oxygen modulates the expression of the catabolic genes encoded by the TOL plasmid.

Changes in pentachlorophenol (PCP) metabolism and physicochemical characteristics by granules responding to different oxygen availability

The effects of oxygen availability on the degradation of pentachlorophenol (PCP) by coupled sludge granules and the granules' physicochemical characteristics were studied in batch experiments. Results indicated that the quantity of available oxygen in serum bottles had a significant effect on the metabolism of PCP. The mass balance analysis of various intermediates (chlorinated phenols and release of chloride ion) indicated that reductive dechlorination was the pathway for the PCP degradation under the studied conditions. The highest degree of mineralization of PCP (95%) was achieved at 40% initial headspace oxygen percentage (IHOP), producing trichlorophenol (TCP), dichlorophenol (DCP), and monochlorophenol (MCP) as the intermediates and chloride as one of the final products in a 3-day incubation period. Under strictly anaerobic or slightly oxidative conditions (0 and 20 IHOP), the reductive dechlorination of PCP caused an accumulation of TCP. Under aerobic conditions (80 and 100 IHOP), PCP degradation was less significant due to the hindered reductive chlorination in the presence of excess oxygen. A positive correlation exists among hydrophobicity, settling velocity, and protein (PN) concentration. The hydrophobicity and PN decreased from 85%, 3.5 mg g−1 VSS to 70%, 1.3 mg g−1 VSS as IHOP increased from 0 to 60, and then increased to 82%, 2.8 mg g−1 VSS as IHOP increased to 100. Oxygen-limited conditions caused an inferior settling characteristic of the granules. Because of a combination of reductive and oxidative degradation mechanisms, aerobic or facultative bacteria were found to oxidize the PCP degradation intermediates produced by methanogens during the metabolism. © 2009 American Institute of Chemical Engineers Environ Prog, 2010

Effects of oxygen saturation on BOLD and arterial spin labelling perfusion fMRI signals studied in a motor activation task

Effects of oxygen availability on blood oxygenation level dependent (BOLD) and arterial spin labelling (ASL) perfusion functional magnetic resonance imaging (fMRI) signal changes upon motor activation were studied. Mild hypoxic hypoxia was induced by reducing the inspired oxygen content (FIO 2) to 12%, decreasing blood oxygen saturation ( Y) from 0.99 ± 0.01 to 0.85 ± 0.03. The fMRI signal characteristics were determined during finger tapping. BOLD activation volume decreased as a function of declining Y in the brain structures involved in execution of the motor task, however, the BOLD signal increase in activated parenchyma was not influenced by Y. ASL fMRI showed that the baseline CBF of 61.8 ± 3.6 ml/100 g/min was not affected by hypoxic hypoxia. Similar to the BOLD fMRI, the volume of motor cortex areas displaying increase in perfusion by ASL fMRI decreased, but the signal change due to perfusion increase was not influenced in hypoxia. The present fMRI results show distinct patterns of haemodynamic and metabolic responses in the brain to motor task between normoxia and hypoxia. On one hand, neither BOLD nor ASL fMRI signal changes are influenced by hypoxia during motor activation. On the other hand, hypoxia attenuates increase in both BOLD and perfusion fMRI signals upon finger tapping from the levels determined in normoxia. These observations indicate that haemodynamic and metabolic responses may be heterogeneous in brain during execution of motor functions in mild hypoxia.

Sensitivity of Brassica oleracea seed germination to hypoxia: A QTL analysis

Reduced oxygen availability can have a major impact on germination and seedling emergence in the field. The effects of oxygen availability on the germination of Brassica oleracea seeds and their sensitivity to hypoxia were investigated to determine whether they have a genetic basis and to identify loci involved in the determination of the trait. Seeds were produced, under the same environmental conditions, from 95 doubled haploid progeny lines of a mapping population from a cross between a rapid cycling Chinese kale (A12DHd) and a calabrese (GDDH33) parent. The sensitivity of the parent lines to oxygen deprivation was characterised at a range of oxygen tensions. Seeds from all lines were then screened for their ability to germinate at 5% oxygen and data were subjected to quantitative trait loci (QTL) mapping analysis. Seed germination from the GDDH33 parent was greater than from the A12DHd parent and sensitivity to reduced oxygen availability segregated in the population in a continuous distribution. Significant QTL were identified on linkage groups O2 and the presence of others on O8 and O9 was suggested. The data indicate that this trait is under genetic control and that the QTL on O8 may be a general stress QTL influencing the rate of germination, whereas that on O2 may be oxygen stress specific and influencing a threshold that determines the number of seeds capable of germination.

Modeling Biofiltration of VOC Mixtures under Steady-State Conditions

Treatment of air streams contaminated with binary volatile organic compound (VOC) mixtures in classical biofilters under steady-state conditions of operation was described with a general mathematical model. The model accounts for potential kinetic interactions among the pollutants, effects of oxygen availability on biodegradation, and biomass diversification in the filter bed. While the effects of oxygen were always taken into account, two distinct cases were considered for the experimental model validation. The first involves kinetic interactions, but no biomass differentiation, used for describing data from biofiltration of benzene/toluene mixtures. The second case assumes that each pollutant is treated by a different type of biomass. Each biomass type is assumed to form separate patches of biofilm on the solid packing material, thus kinetic interference does not occur. This model was used for describing biofiltration of ethanol/butanol mixtures. Experiments were performed with classical biofilters packed with mixtures of peat moss and perlite (2:3, volume:volume). The model equations were solved through the use of computer codes based on the fourth-order Runge-Kutta technique for the gas-phase mass balances and the method of orthogonal collocation for the concentration profiles in the biofilms. Good agreement between model predictions and experimental data was found in almost all cases. Oxygen was found to be extremely important in the case of polar VOCs (ethanol/butanol).

Preservation of organic-walled dinoflagellate cysts in different oxygen regimes: a 10,000 year natural experiment

The occurrence of organic-walled dinoflagellate cysts in (fossil) sediments depends on several factors, including as the ecological preferences of the cyst-forming dinoflagellates, cyst production, transport and preservation. Although laboratory experiments have shown that several cyst species are sensitive to chemical treatment, no information about the selective preservation of dinoflagellate cyst species in natural environments has previously been presented. Here, we present data on the effects of oxygen availability in bottom sediments on a cyst assemblage from the ungraded Madeira Abyssal Plain f-turbidite of which only the upper layer has been oxidized. Based on differences in species composition between the oxidized and underlying, unoxidized layers of this turbidite, the influence of oxygen availability on the preservation of individual species has been estimated. Cyst species have been classified in ascending order of resistance to oxygen availability in sediments as: (1) highly sensitive (cysts formed by Protoperidinium species), (2) moderately sensitive (e.g. Spiniferites species), (3) moderately resistant (e.g. Impagidinium paradoxum and Nematosphaeropsis labyrinthus) and (4) resistant (e.g. Impagidinium aculeatum).

The effects of oxygen availability on the lubricating performance of a dimethyl silicone in the boundary regime

This paper considers the various factors contributing to the poor lubricating performance of silicones in the boundary regime, especially with ferrous metals. Previous published literature indicates that with dimethyl silicones the usual beneficial chemical or physical effects are relatively or completely ineffective. However, it is considered that the severe welding and tearing which occur are due not only to the absence of any favourable boundary effect, but also to some positive harmful influence. Experiments with three different test geometries show that the effects of varying oxygen availability on sliding in the presence of a dimethyl silicone are those which would be anticipated where oxygen starvation is present. Silicones are unlikely to present a physical barrier to oxygen access, but an examination of the limited chemical data available suggests that oxidation of a dimethyl silicone creates an oxygen-starved contact, and that this causes severe adhesive wear.