Changes in the oxygen consumption of cysts of Globodera rostochiensis associated with the hatching of juveniles

The oxygen consumption of single cysts (90–110 /tg dry wt) was measured with an oxygen electrode microrespirometer. The mean oxygen consumption of nine cysts after 7 days in tap-water, was 0–48 + 0–05 mm³ 0₂ mg dry wt^-1 h^-1. After transfer to potato root diffusate for 1 day the mean oxygen consumption of the same cysts showed a significant increase to 159±7% of the rate recorded before they were removed from water. After 3 and 7 days in diffusate the corresponding means were 131±9% and 127±12% respectively. Cysts that remained in water throughout the experiments did not show any significant change in their oxygen consumption from the rate recorded after 7 days. The initial increase in oxygen uptake after the addition of diffusate was shown not to be due to the presence of microorganisms. Comparison of hatching data with the changes in oxygen consumption of similar cysts after 24 h in diffusate suggests that the increased oxygen uptake cannot be attributed solely to locomotor activity of the juveniles during the hatching process. The increased rate of respiration may precede other known changes that follow after the juveniles within a cyst are stimulated to hatch.     

Heterotrophic bacterial activity in Roskilde Fjord sediment during an autumn sedimentation peak

Total oxygen uptake, bacterial oxygen uptake, total bacterial biomass and active bacterial biomass were determined at the sediment-water interface at two stations in the brackish Roskilde Fjord between September and December in 1986 before, during and after sedimentation of a phytoplankton bloom. Bacterial oxygen consumption was separated from total oxygen consumption by addition of cycloheximide. The fractional and the absolute bacterial oxygen uptake were greatest at the most eutrophic station, where total oxygen uptake was 870–1740 mg O₂ m^–2 d^–1 and the bacterial oxygen uptake was 232–870 mg O₂ m^–2 d^–1. At the less eutrophic station, total oxygen uptake was 725–1740 mg O₂ m^–2 d^–1. and bacterial oxygen uptake was 200–550 mg O₂ m^–2 d^–1.Active bacterial biomass was separated from total bacterial biomass by addition of the terminal electron acceptor INT-formazan. The active bacterial biomass was 70–120 µg C mg^–1 ww of sediment at the most eutrophic station and 50–90 µg C g^–1 ww of sediment at the other station. Differences in capacity of bacterial oxygen uptake between the two stations correlated to the active bacterial biomass. The non-temperature dependent bacterial oxygen uptake correlated with the sedimentation rate.     

Inhibition of leukotriene B4-induced neutrophil degranulation by leukotriene B4-dimethylamide

Leukotriene B₄ (LTB₄) is a potent mediator of pro-inflammatory responses including neutrophil degranulation. Leukotriene B₄ dimethylamide has been synthesized and shown to inhibit neutrophil degranulation induced by LTB₄. The inhibition required time to develop (～60 secs), and had a K_D of circa 2 × 10^?7M, and occurred at concentrations where LTB₄ dimethylamide had negligible agonist activity.     

Respiration rate in human primary renal proximal and early distal tubular cells in vitro: considerations for biohybrid renal devices

Background: For biotechnological use of cells in tissue engineered applications, such as biohybrid renal devices, optimal culture conditions are required. Oxygen delivery is one of the most important cell determined system criterion for ex vivo applications. It is involved in the maintenance of highly oxygen‐dependent renal tubular epithelial cells, affecting metabolic state, differentiation, and desired transport functions. The purpose of this study was to examine respiratory patterns such as basal oxygen consumption, solute transport‐related oxygen demand, and oxygen concentration‐dependent oxygen uptake of renal tubular epithelial cells in vitro. Methods: Respiratory patterns of highly purified human primary renal proximal (hPTC) and early distal tubular cells (hTALDC) were analyzed by perfusion respirometry. Spontaneous oxygen consumptions and maximum respirations after carbonyl cyanide m‐chlorophenyl hydrazone (CCCP) uncoupling were measured. Respiration fractions contributing to basolateral Na⁺/K⁺‐ATPase transport activities were assessed via ouabain inhibition and Na⁺‐free medium. Furthermore, we determined oxygen uptake in dependency of oxygen concentration and morphology in various culture conditions (shaken, static). Results: Respiration of solely hPTC strongly depended on oxygen concentration in a Michaelis‐Menten pattern at noncritical oxygen concentrations. Respiration of both cell types was significantly increased by CCCP, whereas average Na⁺/K⁺‐ATPase‐based oxygen uptake fractions differ significantly between the two cell types. Nevertheless, no significant differences were found in spontaneous respiration between hPTC and hTALDC. Conclusions: Our results clearly indicate that cell‐specific oxygen consumption parameters have to be considered in the design of biotechnological devices intended to support kidney function by cell‐supported renal replacement therapy. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Insulin‐ and Exercise‐Stimulated Skeletal Muscle Blood Flow and Glucose Uptake in Obese Men

Objective: Insulin resistance in obese subjects results in the impaired use of glucose by insulin‐sensitive tissues, e.g., skeletal muscle. In the present study, we determined whether insulin resistance in obesity is associated with an impaired ability of exercise to stimulate muscle blood flow, oxygen delivery, or glucose uptake. Research Methods and Procedures: Nine obese (body mass index = 36 ± 2 kg/m²) and 11 age‐matched nonobese men (body mass index = 22 ± 1 kg/m²) performed one‐legged isometric exercise during hyperinsulinemia. Rates of femoral muscle blood flow, oxygen consumption, and glucose uptake were measured simultaneously in both legs using [¹⁵O]H₂O, [¹⁵O]O₂, [¹⁸F]fluoro‐deoxy‐glucose, and positron emission tomography. Results: The obese subjects exhibited resistance to insulin stimulation of glucose uptake in resting muscle, regardless of whether glucose uptake was expressed per kilogram of femoral muscle mass (p = 0.001) or per the total mass of quadriceps femoris muscle. At similar workloads, oxygen consumption, blood flow, and glucose uptake were lower in the obese than the nonobese subjects when expressed per kilogram of muscle, but similar when expressed per quadriceps femoris muscle mass. Discussion: We conclude that obesity is characterized by insulin resistance of glucose uptake in resting skeletal muscle regardless of how glucose uptake is expressed. When compared with nonobese individuals at similar absolute workloads and under identical hyperinsulinemic conditions, the ability of exercise to increase muscle oxygen uptake, blood flow, and glucose uptake per muscle mass is blunted in obese insulin‐resistant subjects. However, these defects are compensated for by an increase in muscle mass.     

16O2/18O2 analysis of oxygen exchange in Dunaliella tertiolecta. Evidence for the inhibition of mitochondrial respiration in the light

A mass spectrometric ¹⁶O₂/¹⁸O₂-isotope technique was used to analyse the rates of gross O₂ evolution, net O₂ evolution and gross O₂ uptake in relation to photon fluence rate by Dunaliella tertiolecta adapted to 0.5, 1.0, 1.5, 2.0 and 2.5 M NaCl at 25°C and pH 7.0.At concentrations of dissolved inorganic carbon saturating for photosynthesis (200 M) gross O₂ evolution and net O₂ evolution increased with increasing salinity as well as with photon fluence rate. Light compensation was also enhanced with increased salinities. Light saturation of net O₂ evolution was reached at about 1000 mol m^-2s^-1 for all salt concentrations tested. Gross O₂ uptake in the light was increased in relation to the NaCl concentration but it was decreased with increasing photon fluence rate for almost all salinities, although an enhanced flow of light generated electrons was simultaneously observed. In addition, a comparison between gross O₂ uptake at 1000 mol photons m^-2s^-1, dark respiration before illumination and immediately after darkening of each experiment showed that gross O₂ uptake in the light paralleled but was lower than mitochondrial O₂ consumption in the dark.From these results it is suggested that O₂ uptake by Dunaliella tertiolecta in the light is mainly influenced by mitochondrial O₂ uptake. Therefore, it appears that the light dependent inhibition of gross O₂ uptake is caused by a reduction in mitochondrial O₂ consumption by light.Abbreviations DCMU 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea - DHAP dihydroxy-acetonephosphate - DIC dissolved inorganic carbon - DR_a rate of dark respiration immediately after illumination - DR_b rate of dark respiration before illumination - E₀ rate of gross oxygen evolution in the light - NET rate of net oxygen evolution in the light - PFR photon fluence rate - RubP rubulose-1,5-bisphosphate - SHAM salicyl hydroxamic acid - U₀ rate of gross oxygen uptake in the light     

In situ analysis of oxygen consumption and diffusive transport in high‐temperature acidic iron‐oxide microbial mats

The role of dissolved oxygen as a principal electron acceptor for microbial metabolism was investigated within Fe(III)‐oxide microbial mats that form in acidic geothermal springs of Yellowstone National Park (USA). Specific goals of the study were to measure and model dissolved oxygen profiles within high‐temperature (65–75°C) acidic (pH = 2.7–3.8) Fe(III)‐oxide microbial mats, and correlate the abundance of aerobic, iron‐oxidizing Metallosphaera yellowstonensis organisms and mRNA gene expression levels to Fe(II)‐oxidizing habitats shown to consume oxygen. In situ oxygen microprofiles were obtained perpendicular to the direction of convective flow across the aqueous phase/Fe(III)‐oxide microbial mat interface using oxygen microsensors. Dissolved oxygen concentrations dropped from ～ 50–60 μM in the bulk‐fluid/mat surface to below detection (< 0.3 μM) at a depth of ～ 700 μm (～ 10% of the total mat depth). Net areal oxygen fluxes into the microbial mats were estimated to range from 1.4–1.6 × 10^?4 μmol cm^?2 s^?1. Dimensionless parameters were used to model dissolved oxygen profiles and establish that mass transfer rates limit the oxygen consumption. A zone of higher dissolved oxygen at the mat surface promotes Fe(III)‐oxide biomineralization, which was supported using molecular analysis of Metallosphaera yellowstonensis 16S rRNA gene copy numbers and mRNA expression of haem Cu oxidases (FoxA) associated with Fe(II)‐oxidation.     

Interferon inhibition of thymidine incorporation into DNA through effects on thymidine transport and uptake

Replenishment of medium after 72 hr of growth of HeLa-S3 cells in dense suspension cultures increased [³H]-thymidine uptake into cells and incorporation into DNA, with the levels reaching a peak ～ 12 hr following medium change; β interferon inhibits the enhanced uptake of [³H]-thymidine and labeling of DNA in a dose-dependent manner. Some reduction in these processes is observed at a concentration as low as 1 u/ml, and ～ 75% inhibition at 640 u/ml. Kinetic analysis has revealed that the rate of labeling of the acid-soluble pool with [³H]-thymidine, measured either at 22°C, or 37°C, is reduced in interferon-treated (640 u/ml, 24 hr) HeLa-S3 cells. At 22°C, the initial rate of thymidine transport at a high (500 μM) thymidine concentration, determined within the first 30 sec of [³H]-thymidine addition was depressed by 44% in interferon-treated HeLa cells. At 37°C, labeled precursors accumulate in acid-soluble material for ～ 8 min after the addition of [³H]-thymidine, after which an apparent equilibrium level is attained. At this temperature, the rate of thymidine uptake and the apparent equilibrium level attained were depressed by 70% in interferon-treated HeLa cells. The reduced incorporation of [³H]-thymidine into DNA in interferon-treated HeLa-S3 cells can be largely explained by interferon inhibition of thymidine transport and phosphorylation.     

Effect of meal and propranolol on whole body and splanchnic oxygen consumption in patients with cirrhosis

Our aim was to measure whole body energy expenditure after a mixed liquid meal, with and without simultaneous propranolol infusion, in patients with cirrhosis. We also wanted to investigate the effect of propranolol on substrate fluxes and oxygen uptake in the tissues drained by the hepatic vein and azygos vein in the postprandial period in these patients. Whole-body oxygen uptake, hepatic blood flow, hepatic venous pressure gradient and net-hepatic fluxes of oxygen, lactate, glucose, glycerol, and free fatty acids (FFA) were measured in 12 patients with alcoholic cirrhosis before and for 2 h after ingestion of a mixed liquid meal (700 kcal). Half of the patients (n = 6) were randomized to a treatment group receiving intravenous infusion of propranolol in combination with the meal. The meal-induced energy expenditure was significantly lower in patients given propranolol [15.0 +/- 18.9 vs. 67.0 +/- 26.1 kJ/120 min (means +/- SD), P < 0.01]. Meal-induced whole body oxygen uptake was lower in patients receiving propranolol (19.2 +/- 38 vs. 135.7 +/- 61 mmol/120 min, P < 0.01), and the meal-induced increase in splanchnic oxygen uptake was nonexistent when propranolol was administered in combination (-13.2 +/- 34.8 vs. 110.4 +/- 34.8 mmol/120 min, P = 0.04). Postprandially, the propranolol group had a tendency toward a reduced splanchnic glucose output, and the FFA uptake was significantly reduced. Propranolol reduces meal-induced whole body oxygen uptake and energy expenditure as well as splanchnic oxygen uptake. The splanchnic reduction in oxygen consumption can explain almost the entire reduction in whole body oxygen consumption.     

Meiobenthos and the oxygen budget of an intertidal sand beach

Field and laboratory experiments are used to construct a partial oxygen budget for a typical fine sand area just above mean tide level in Strangford Lough, Northern Ireland. Oxygen consumption was determined mainly from batch respiration using a YSI electrode. Experiments with different batch sizes indicate that oxygen uptake rate per individual decreased as the number in the test chamber increased. Experiments conducted monthly at ambient environmental temperature with batches of 40 individuals show minimum oxygen consumption occurred at 12 °C in the nematode, copepod and turbellarian populations tested.Modelling the situation for 1 m² of beach in November 1979 gives a meiofaunal demand from 295,250 individuals of a total 40 ml O₂ . h^–1 compared with an estimated 2760 for macrofauna and 1172 for sediment with attached microorganisms. Microfloral production was calculated as 324 ml O₂ . h^–1 in light. The individual meiofaunal respiration values are much higher than those previously reported. The reasons for this and the confidence which can be attached to these and other workers results are discussed. Information from laboratory and field results is used to construct a partial oxygen budget for a typical fine sand area just above mid-tide level in Strangford Lough, Northern Ireland. Oxygen consumption by meiofaunal taxa and Hydrobia was determined from batch respiration experiments using a YSI oxygen electrode, as was consumption and production by sediment with attached microflora. Experiments conducted monthly at ambient temperature indicate minimum oxygen consumption at 12 ° C in the nematode, copepod and turbellarian (Monocelopsis sp.) population tested. Batch size affected consumption; with nematodes, copepods and gastrotrichs (Turbanella varians) uptake per individual decreased as number in the test chamber increased. Later experiments were therefore conducted with a standard batch size of 40 individuals.Inspection of biological and physical data showed conditions in November 1979 were close to the annual mean. Using these and the appropriate laboratory data the calculated values give a meiofaunal oxygen demand per m² of beach of 40 ml h^–1 compared with an estimated 2760 for the macrofauna and 1172 for the sediment with attached micro-organisms. Microfloral oxygen production was 324 ml h^–1 in light. The meiofaunal figures are based on a population of 295,250 individuals per m² with a percentage composition of Nematoda 58.2, Copepoda 22.7, Gastrotricha 14.4, Turbellaria 5.3 and Gnasthostomulida 1.3. These figures give a relative population oxygen uptake of 50.1 : 32.3 : 5.1 : 9.9 : 2.7% respectively. The confidence which can be attached to these and other workers results is discussed.     

The effect of dissolved oxygen tension and the utility of oxygen uptake rate in insect cell culture

Dissolved oxygen tension and oxygen uptake rate are critical parameters in animal cell culture. However, only scarce information of such variables is available for insect cell culture. In this work, the effect of dissolved oxygen tension (DOT) and the utility of on-line oxygen uptake rate (OUR) measurements in monitoring Spodoptera frugiperda (Sf9) cultures were determined. Sf9 cells were grown at constant dissolved oxygen tensions in the range of 0 to 30%. Sf9 metabolism was affected only at DOT below 10%, as no significant differences on specific growth rate, cell concentration, amino acid consumption/production nor carbohydrates consumption rates were found at DOT between 10 and 30%. The specific growth rate and specific oxygen uptake rate followed typical Monod kinetics with respect to DOT. The calculated _max and max were 0.033 h^-1 and 3.82×10^-10 mole cell^-1h^-1, respectively, and the corresponding saturation constants were 1.91 and 1.57%, respectively. In all aerated cultures, lactate was consumed only after glucose and fructose had been exhausted. The yield of lactate increased with decreasing DOT. It is proposed, that an apparent DOT in non-instrumented cultures can be inferred from the lactate yield of bioreactors as a function of DOT. Such a concept, can be a useful and important tool for determining the average dissolved oxygen tension in non-instrumented cultures. It was shown that the dynamic behavior of OUR can be correlated with monosaccharide (fructose and glucose) depletion and viable cell concentration. Accordingly, OUR can have two important applications in insect cell culture: for on-line estimation of viable cells, and as a possible feed-back control variable in automatic strategies of nutrient addition.Abbreviations DOT Dissolved oxygen tension - OUR Oxygen uptake rate - specific oxygen uptake rate - specific growth rate - X_v viable cell concentration - C_L, C^*, and oxygen concentrations in liquid phase, in equilibrium with gas phase, and medium molar concentration, respectively - H Henry's constant - K_La volumetric oxygen transfer coefficient - P_T total pressure - oxygen partial pressure - oxygen molar fraction - i discrete element     

A sensitive measurement of oxygen uptake rate using a optochemical sensor

Summary The measurement of the specific oxygen uptake rate (OUR) of slow growing organisms using a small sample size is often hampered by the consumption of oxygen by the electrode used. Using a optochemical sensor we measured the OUR of carrot embryos with approximately 1000 cell clusters and of hybridoma with approximately 10⁶ cells. An OUR as low as 0.02 mol/h can be accurately measured.     

The aerobic mineralization of organic compounds in the saline Lake Grevelingen (The Netherlands) (VI)

Summary During a one year period the uptake of aspartic acid and of a mixture of amino acids was determined using¹⁴C-labeled substrates as described by WRIGHT and HOBBIE (1966). By this technique the activity is analyzed of that part of the bacterial population which is able to utilize the added substrate. For comparison purposes the activity of the total heterotrophic bacterial population was determined by measurement of the oxygen consumption rate. From the oxygen consumption rate (mg O₂.l^–1.h^–1) the carbon mineralization rate (mg C.l^–1.h^–1) was calculated by applying a conversion factor of 0.29.Aspartic acid was respired for 80% and the amino acid mixture for 43%. From the maximum uptake rates, the potential yearly uptake of the substrate in question can be calculated. These data indicate the relative importance of the several subpopulations in the carbon mineralization process as a whole. The highest value of the potential yearly uptake was obtained for the amino acid mixture; the comparable value for the uptake of aspartic acid was slightly lower.The carbon mineralization rate as calculated from the oxygen uptake experiments was about 150–200 g C.m^–2.year^–1. The potential yearly uptake as determined with the¹⁴C-labeled amino acid mixture was only 2.8% of the amount of mineralized carbon, as calculated from the oxygen uptake experiments. This percentage is very low in view of the fact that 35–55% of the organic carbon of living phytoplankton and zooplankton consists of protein (HAGMEIER, 1961) and that the aerobic mineralization of amino acids is a very common property among the heterotrophic bacterial population (SEPERS, 1979). The value of the applied activity measurements was investigated in order to obtain information about the relation between the uptake process as measured with¹⁴C-labeled substrates and the activity of the bacterial population in situ. The results of this study have been published bij SEPERS and VAN ES (1979).     

Diversity of juvenile fish assemblages in the pelagic waters of Lebanon (eastern Mediterranean)

Oxygen consumption rates of nauplii of the brine shrimp Artemia franciscana Kellogg 1906 were determined over a range of salinities from 10 to 110 ppm, in temperatures from 0 to 30°C, using a multi-factorial design. The oxygen micro-sensors employed have a fast response time and are capable of accurately measuring oxygen concentrations at temperatures well below 0°C. Oxygen uptake rate ranged from 0.03 to 0.66 μmol O₂ mg⁻¹ h⁻¹ and was sensitive to changes in both salinity and temperature. Temperature was the dominant factor affecting oxygen consumption rates, which showed a significant increase with increasing temperature. A slight decrease was measured in oxygen consumption with increasing salinity related to differential solubility of oxygen in waters of different salinities. Thermal sensitivity of oxygen consumption determined from calculations of Q ₁₀, indicated physiological adaptation of Artemia nauplii to the ranges of temperatures tested. Handling editor: A. van Kerchove     

Respiratory Levels and Adaptations in Four Freshwater Species of Gammarus (Crustacea: Amphipoda)

Respiration of four freshwater species of the amphipod crustacean Gammarus: G. fossarum, G. lacustris (river and lake), G. pulex and G. roeseli were measured in a closed, stirred respirometric chamber with a micro-electrode. Oxygen consumption, expressed as weight-specific oxygen uptake (R_s) in relation to decreasing oxygen concentration, varied at air saturation from 0.86 (G. lacustris, lake) to 2.06 μl O₂ mg⁻¹ AFDW h⁻¹ (G. pulex). R_s also differed intra-specifically among the two populations of G. lacustris. G. lacustris (river), G. pulex and G. roeseli expressed moderate ability to regulate their oxygen consumption at decreasing oxygen concentrations, whereas the regulation ability was higher in G. lacustris (lake) and in G. fossarum, which maintain high oxygen uptake at oxygen levels >2 mg O₂ l⁻¹. All four Gammarus species are partial regulators in response to variations in oxygen concentration. The differences between species are considered too small to account for their natural distributions. It appears that the tolerances of Gammarus species to organic pollution depend only in part on oxygen conditions.     

Effect of cryostorage on oxygen uptake and autograft viability of rat skin

The pre- and post-thawing oxygen uptake of rat skin treated with either 0.9% NaCl or 10% DMSO was compared with the gross survival of skin autografts. Little change was observed in the average oxygen consumption of freshly excised samples taken 28 days apart. Soaking for 2 hr in 10% DMSO decreased oxygen consumption about 29% and freeze-thawing caused a further decrease in oxygen uptake. DMSO soaked, frozen and thawed grafts (studied 28 days after grafting) had a 12% higher oxygen utilization than freshly excised skin. Only 5 of 19 autografts soaked in 0.9% NaCl became functional, but 21 of 38 skin samples soaked in 10% DMSO became functional autografts. The oxygen consumption of the 21 takes was not significantly different from the non-takes. An analysis of variance showed that oxygen utilization of skin subsamples could not reliably predict autograft viability after freeze-storage.     

Toxic effects of zinc and iron on the routine oxygen consumption of Tilapia sparrmanii (Cichlidae)

1. The routine oxygen consumption of Tilapia sparrmanii without the addition of any toxicants over a 72 hr period showed a decrease for the first 48 hr, but stabilised thereafter.2. Addition of zinc (98 mg l⁻¹) resulted in a drastic decrease of oxygen consumption for 3 hr. The routine oxygen consumption showed a significant decrease for the first 24 hr, while the second and third 24 hr revealed significant differences with great individual variance.3. The decrease in oxygen consumption observed after exposure to zinc, could be caused by gill damage as well as the internal action of zinc.4. An increase in oxygen consumption was noted for almost 3 hr after addition of iron (88mg l⁻¹). During the first-, second- and third 24 hr the oxygen consumption increased significantly, compared to the control values.5. The increase in routine oxygen consumption of T. sparrmanii when compared to control values after exposure to iron, could be attributed to stress and possible gill changes.6. The study revealed that after acute (72 hr) exposure to sublethal concentrations of zinc and iron, the routine oxygen consumption of T. sparrmanii was altered.     

Seasonal microbial activity in Antarctic freshwater lake sediments

Summary Seasonal fluctuations in population numbers and activity were monitored in bottom sediments of oligotrophic Moss Lake, mesotrophic Heywood Lake and eutrophic Amos Lake on Signy Island, South Orkney Islands, during 1976–78. Heywood and Amos Lakes became anoxic under winter ice cover (8–10 months) and significant populations of facultatively anaerobic heterotrophs and sulphate-reducing bacteria developed. In contrast, Moss Lake surface sediments never became anoxic and anaerobic bacteria were virtually absent. Direct microscopic counts and viable plate counts fluctuated relatively little in Moss Lake throughout the study period, whereas distinct seasonality was observed in the more enriched lake systems. Similarly, measurements of oxygen consumption and dark ¹⁴CO₂ uptake by mud cores indicated no obvious seasonal fluctuations in Moss Lake data, in contrast to the marked seasonal pattern observed in data from the other lakes. In these latter systems, oxygen uptake rates were highest in summer (c. 400 mg O₂ m^-2 d^-1) and virtually undetectable in winter. Comparison of oxygen uptake with oxygen concentration and temperature revealed differences, between lakes, in uptake response to oxygen concentration, whereas uptake response to temperature did not differ significantly between lakes. Chemosynthetic production in the Signy Island lake sediments was in the range 1.6–35.3 g C m^-2 (mud surface) d^-1 with highest values recorded in Amos Lake under winter ice cover and anoxic conditions. The findings from this and earlier studies of the three lakes have been assembled to indicate the relative importance of green plants and bacteria to the carbon cycle in these permanently cold systems.     

Advantages of NH4 + on growth, nitrogen uptake and root respiration of Phragmites australis

We investigated growth, N nutrition, and root respiration in Phragmites australis (Cav.) Trin. ex Steud. grown under conditions with different N sources, and evaluated the advantages of NH₄ ⁺ nutrition in relation to adaptation to anaerobic soil conditions. Hydroponics culture was carried out for 2 months under two treatment conditions with different N sources, NH₄ ⁺ and NO₃ ^?. The relative growth rate (RGR) of the roots, shoot and whole plant, net N uptake rate (NNUR), and root respiration rate were examined. Shoot RGR, shoot to root (S/R) ratio, and NNUR were obviously higher with the NH₄ ⁺ treatment. High S/R ratio of plants grown in the NH₄ ⁺ treatment contributed to repression of whole-root oxygen consumption. In consequence, NNUR per root respiration rate was higher with the NH₄ ⁺ treatment, which clearly suggested efficient oxygen consumption in the roots. In conclusion, higher S/R ratio due to higher NNUR enable to efficiently use oxygen for N nutrition through the repression of whole-root oxygen consumption, which is consequently achieved by NH₄ ⁺ nutrition. Therefore, we suggest that NH₄ ⁺ nutrition is indispensable for hydrophytic species growing in anaerobic soil because it enables both sufficient N nutrition and efficient oxygen consumption.