Effect of oxygen on the growth (yield) of Chlorella vulgaris

The growth yield of Chlorella vulgaris, Y _kJ defined as g cells harvested per kJ of light energy absorbed by the cells, was assessed in a turbidostat culture by varying CO₂ and O₂ partial pressures ( and ). The value of Y _kJ ranged from 3.1×10^-3 to 5.0×10^-3 g cells/kJ under light-limited conditions [ = 1.02.4%, = 065%; total pressure of gas (composed of CO₂, O₂ and N₂)=1 atm]. In the light-limited environment, the algal specific growth rate deteriorated appreciably with the increase of . The deterioration accounts for the above range of Y _kJ observed. The growth inhibition due to oxygen that was defined by subtracting from 1.0 the ratio of at given values of to that at = 0% extended from 0.07–0.30 (7–30%). However, glycolate could not be detected in the turbidostat culture. Isotopic experiments on the specific rate of ¹⁴CO₂ uptake also revealed that the inhibition due to oxygen was from 22–38% when was varied from 0 to nearly 100%. These effects of oxygen were discussed, referring to the activity of ribulose-1,5-bisphosphate carboxylase that is inhibited competitively by oxygen.Non-Standard Abbreviations INH isonicotinic acid hydrazide - PPO 2,5-diphenyloxazole - DCMU 3-(-3,4-dichlorophenyl)-1,1-dimetylurea - CA carbonic anhydrase - RuP₂ ribulose-1,5-bisphosphate     

Oxygen consumption of Phycomyces sporangiophores

Summary The respiration of stage-I,-III, and-IV sporangiophores of Phycomyces was measured. The of stages-I and-IV is low compared to that of actively growing mycelium. The of stage-III sporangiophores is somewhat higher than that of stages-I and-IV. As stage-I sporangiophores elongate their respiration rate increases proportionately. The respiration rate of stage-IV sporangiophores does not change as they elongate. In stage-IV sporangiophores the growing zone and the columella together consume as much oxygen as the rest of the sporangiophore does. Changes in the sporangiophore's growth rate have no effect on its oxygen consumption.This work was submitted in partial fulfillment of the requirements for the Ph. D. degree.     

Growth yields and saturation constant of Desulfovibrio vulgaris in chemostat culture

Desulfovibrio vulgaris (strain Marburg) was grown on H₂ and sulfate as sole energy source in a chemostat limited by the sulfate supply. The biomass concentration and the sulfate concentration in the culture were determined as a function of the dilution rate. From the data a K _S (saturation constant) for sulfate of 10 M, a _max of 0.23 h^–1, and a of 13 g/mol were calculated. The organism was also grown in chemostat culture on H₂ and sulfite, H₂ and thiosulfate, and pyruvate (without sulfate). was found to be 35 g/mol, 36 g/mol, and Y _pyr ^max 10 g/mol. The growth yields are discussed with respect to ATP gains in dissimilatory sulfate reduction.     

Energy requirements of Adélie penguin (Pygoscelis adeliae) chicks

Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O₂ consumption ( ) and CO₂ production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from in lying chicks to at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities ( ), and one for walking ( ). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as , whereas mass-specific O₂ consumption was related to walking speed (S, m·s^-1) as .Abbreviations bpm beats per minute - D distance walked (m) - ECG electrocardiogram - HR heart rate (bpm) - ns number of steps - RQ respiratory quotient - S walking speed (m·s^-1) - T time walked (s) - W body mass (kg)     

Nitrate reductase in needles,roots and trunk wood of spruce trees [Picea abies (L.) Karst.]

Summary Nitrate reductase (EC 1.6.6.2) activity (NRA), as measured by an in vivo assay, is present in needle leaves and mycorrhizal fine root tips of adult Norway spruce [Picea abies (L.) Karst.] in at least equal amounts on a fresh weight basis, in both adult and 5-year-old trees. NRA could also be demonstrated in trunk wood of deroted trees after fertilization with 5 mM , exhibiting a longitudinal profile in the trunk. Inducibility in needles can more efficiently be achieved by NO₂ (100 g·m^-3) than by 5 mM nitrate, which is effective only in root-amputated trees. A remarkably high level of needle-NRA in unfertilized trees, which are characterized by a very low level of nitrate in the xylem sap, suggests that NRA in spruce needles may in part be constitutive. Organic-N is a major nitrogen source for the needles even in root-amputated trees, indicating pronounced exchange processes between ray parenchyma and trunk xylem, which in turn are modified by the nitrogen source fed to the trunk stump. Intact trees exhibit a very similar amino acid composition of the xylem sap, regardless of whether or has been fed. The amino acid pattern of the needles is not thrown out of balance by flooding with and , which occurs in fertilized derooted trees. This indicates a distinct potential for homoeostasis of nitrogen entrance-metabolism (i.e. NRA and glutamine synthetase activity) in the needles. In the ectomycorrhiza/fine root-system (EMC), marked differences in NRA were observed depending on root-tip diameter and along the longitudinal profile of the fine roots. EMC-nitrate reductase is strongly enhanced by . Needle-NRA exhibits a circannual rhythm. An early summer maximum is followed by a December minimum. This activity pattern matches well the transitory increase of soluble nitrogen in spring and the total protein maximum in winter. In an indirect way assimilatory NRA may well contribute to nitrogen overfertilization (by consumption of NO_X) as one possible cause of the contemporary decline of spruce populations.     

Gill function in an elasmobranch

Summary Highly efficient oxygen uptake in elasmobranchs, as indicated by frequent excess of over has previously been ascribed to the operation of multicapillary rather than counter-current gas exchange by the gills. Analysis of models shows that, at maximum efficiency, a multicapillary system cannot account for values of greater than . In Port Jackson sharks Heterodontus portusjacksoni) commonly exceeds , which indicates the operation of a functional counter-current at the respiratory surface. The anatomical basis of this counter-current is provided by the demonstration that a continuous flow of water passes between the secondary lamellae into septal canals and thence via the parabranchial cavities to the exterior.Queen Elizabeth II Fellow.     

A comparative study of the mechanism of Na+ and Cl? excretion by the gill ofMugil capito andFundulus heteroclitus: Effects of Stress

Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na⁺ and of Cl^– and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not . InFundulus, is also decreased. Transfer of the two species from SW to fresh water (FW) reduces and by 75 to 85% and leads to a large inversion of P.D. When K⁺ is added to FW, a gill depolarization occurs, as well as a large increase of and .These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na⁺ ( ) being greater than that to Cl^– ( ), 2) a Cl^–/Cl^– exchange independent of P.D. is associated with the Cl^– pump; 3) Cl^– pump activity is linked to Na⁺/K⁺ exchange which in turn is associated to a Na⁺/Na⁺ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of and observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of which becomes equal to in both species.As a result of stress, the K⁺-activated Na⁺ and Cl^– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil.     

Regulation of the utilization of 4-hydroxybenzoate and 4-hydroxycinnamate in batch and continuous cultures of Pseudomonas testosteroni

Pseudomonas testosteroni metabolized 4-hydroxycinnamate by an initial cleavage of the side chain to yield acetate and the aromatic moiety, 4-hydroxybenzaldehyde. The latter was further oxidized via 4-hydroxybenzoate to protocatechuate, which underwent meta cleavage. During growth of the organism on 4-hydroxycinnamate, the for acetate showed an undulating pattern, which was attributed to alternating induction and repression of enzymes involved in the oxidation of acetate. Repression was caused either by 4-hydroxybenzoate or by its later metabolites, formate and pyruvate.In batch culture, P. testosteroni oxidized mixtures of 4-hydroxybenzoate and 4-hydroxycinnamate in a diauxic pattern. The capacity to oxidize 4-hydroxycinnamate appeared in the cells before 4-hydroxybenzoate was exhausted, indicating that the enzymes catalysing the conversion of 4-hydroxycinnamate into 4-hydroxybenzoate. were induced despite the presence of 4-hydroxybenzoate. The induction of these early enzymes of 4-hydroxycinnamate catabolism started when the molar concentration ratio of 4-hydroxybenzoate to 4-hydroxycinnamate fell below a value of 0.3.In continuous culture of P. testosteroni on a mixture of 4-hydroxybenzoate and 4-hydroxycinnamate, both substrates were almost completely utilized up to a dilution rate of about 0.5/h. At higher dilution rates, 4-hydroxycinnamate was decreasingly utilized so that eventually at a dilution rate of 0.74/h, its effluent concentration equalled its influent concentration. At D _M, a utilization ratio of 1.23 in favour of 4-hydroxybenzoate was found to become established in the culture. The of the cells for acetate was maximal at a dilution rate of 0.38/h and decreased before 4-hydroxycinnamate utilization was at its peak at 0.59/h. This suggested that it was mainly the aromatic moiety of 4-hydroxycinnamate which was metabolized at high dilution rates. The failure to utilize acetate at high dilution rates was apparently due to the repression of its catabolic enzymes by later metabolites of 4-hydroxybenzoate and to the relatively low concentration of acetate in the fermenter. This low concentration, due to the continuous washout of acetate, prevented it from relieving the repression.Abbreviations 4HB 4-hydroxybenzoate - 4HC 4-hydroxycinnamate - D _M dilution rate allowing maximal cell output rate - OD optical density     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

Water relations of buried eggs of mound building birds

Summary Eggs of the brush turkey (BT) and mallee fowl (MF) are incubated in mounds of soil and plant litter. Humidity in BT mounds is always near saturation (>99% RH), but in MF mounds it drops to lower values in summer (x=77% RH). Despite these high humidities, the eggs lose an average of 9.5% (BT) and 12.0% (MF) of their initial mass by evaporation before hatching. The rate of evaporation increases during incubation several-fold due to large changes in water vapor conductance of the shell and embryonic heat production. Values of in fully incubated eggs in mound material are about 3–6 times higher than values obtained from unincubated eggs in desiccators. This effect depends on two factors: (1) increases with ambient humidity, especially above 80% RH, possibly because the effective site of evaporation moves out along the walls of the pores in the eggshell. (2) Structural changes of the pores due to calcium absorption by the embryo directly increase . The first factor is most important in BT eggs and the second is dominant in MF eggs. Production of metabolic heat by the embryo increases the vapor pressure difference across the shell and further increases , especially in mounds of high humidity. The changes in pore structure are adaptive because they produce high conductances to respiratory gases and cause normal gas tensions within the egg at the end of development, yet is low enough in early development to prevent excessive water loss. Water not lost by evaporation or taken up by the embryo is stored and released during hatching. A small amount of mass is lost during incubation by respiratory gas exchange.Abbreviations BT brush turkey - MF mallee fowl - RH relative humidity     

Water economy in bird nests

Summary Nest humidity ( ) under an incubating bantam hen was measured at ambient ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest and ambient were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest increased linearly with ambient in a way predictable on the assumption that the water vapour conductance ( ) of brood patch skin, plumage and eggs were constant and independent of ambient . Nest was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest at varying ambient . Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations water vapur pressure - water vapur conductance - water flux     

Thermoregulation,gas exchange,and ventilation in Adelie penguins (Pygoscelis adeliae)

Summary Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (T _a) in their natural habitat. We examined body temperature (T _b), oxygen consumption ( ), carbon dioxide production ( ), evaporative water loss ( ), and ventilation atT _a from –20 to 30 °C. Body temperature did not change significantly between –20 and 20°C (meanT _b=39.3°C).T _b increased slightly to 40.1 °C atT _a=30°C. Both and were constant and minimal atT _a between –10 and 20°C, with only minor increases at –20 and 30°C. The minimal of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g·min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at allT _a. Values of were low at lowT _a, but increased to 0.21 g/min at 30°C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between –20 and 30°C. Evaporative heat loss (EHL) comprised about 5% of MHP at lowT _a, rising to 47% of MHP atT _a=30°C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [I], and oxygen extraction [ ]) were fairly stable between –20 and 10°C (VT did not change significantly over the entireT _a range). However, there was considerable inter- and intra-individual variation in ventilation patterns. AtT _a=20–30°C,f increased 7-fold over the minimal value of 7.6 breaths/min, and I showed a similar change. fell from 28–35% at lowT _a to 6% atT _a=30°C.Abbreviations C thermal conductance - EHL evaporative heat loss - oxygen extraction - f respiratory frequency - MHP metabolic heat production - evaporative water loss - LCT lower critical temperature - RE respiratory exchange ratio - T _a ambient temperature - T _b body temperature - rate of oxygen consumption - rate of carbon dioxide production - I inspiratory minute volume - VT tidal volume     

Physiological mechanisms for underwater endurance: Canada goose (Branta canadensis) versus Pekin duck (Anas platyrhynchos)

Maximum submergence time of Canada geese was 18% of that of similarly sized Pekin ducks. Due to a smaller respiratory system volume the oxygen store of Canada geese was 82% of that of Pekin ducks, accounting for approximately 33% of the difference in underwater survival times. The respiratory properties and volume of the blood were similar in both species. Both species utilised approximately 79% of the respiratory oxygen store and 90% of the blood oxygen store. Therefore, most of the species difference in survival times was due to a less effective oxygen-conserving cardiovascular response (bradycardia, peripheral vasoconstriction) in Canada geese. Duck cardiac chronotropic sensitivity to hypoxia during submergence was twice that observed in geese. Furthermore, a lower hypoxic ventilatory response was observed in geese than in ducks. Density of monoamine varicosities in hindlimb artery walls was lower in geese than ducks. However, electrical stimulation of the hindlimb muscles did not cause ascending vasodilation during submergence in either species, perhaps due to higher levels of catecholamines in submerged geese. We conclude that the major difference between species is higher oxygen chemosensitivity in ducks which effects a much more rapid and efficacious oxygen-conserving response during forced submergence.Abbreviations ATPS · BTPS · STPD CNS central nervous system - EEG electroencephalogram - ECG electrocardiogram - EDTA ethylenediaminetetra-acetic acid - HPLC high performance liquid chromatography - fractional oxygen concentration of inspired air - pre-immersion fractional concentration of oxygen in the respiratory system - pre-emersion fractional concentration of oxygen in the respiratory system - [Hb] haemoglobin concentration - Hct haematocrit - HR heart rate - M _B body mass - M _b brain mass - M _h heart mass - partial pressure of carbon dioxide in arterial blood - partial pressure of oxygen in arterial blood - SPG sucrose-potassium phosphate-glyoxylic acid - t _d maximum underwater survival time - respiratory minute volume - V _pl plasma volume - V _rs respiratory system volume - accessible respiratory system oxygen store - total non-myoglobin-bound oxygen store - V _tb blood volume - blood oxygen store     

Effects of variation in total and regional shell conductance on air cell gas tensions and regional gas exchange in chicken eggs

Summary Gas conductance of the shell, rates of O₂ consumption, CO₂ production and air cell gas tensions were measured in pre-internal pipping, 19 day-old chicken eggs that were selected for a wide range in shell conductance. Regional conductance was measured in eggs with partially waxed shells.Surface-specific shell conductance was not uniform over the egg; it was over 3-fold higher at the poles than at the equator. Conductance was about 59% higher over the air cell than over the chorioallantoic part of the egg. Surface-specific perfusion was 12% higher in the air cell. Therefore the in the air cell was higher, and the lower, than values calculated for the whole egg. The mean difference in between the air cell and the chorioallantoic part of the egg was 14.8 Torr, and that of , was 7.0 Torr. These differences were somewhat dependent on total conductance. Respiratory gas exchange ratio ( ) was higher in the air cell (R=0.82) and lower in the chorioallantoic region (R=0.67) than for the whole egg (R=0.70). Air cell R increased slightly in eggs of higher total conductance.Mismatching of regional shell conductance and chorioallantoic perfusion contributes to a functional venous shunt that is partly responsible for nonequilibrium between the air cell and the blood in the chorioallantoic veins.Symbols and abbreviations D gas diffusity - F _A fractional surface area - F _G fractional conductance - G conductance - G _diff diffusion conductance - G _perf perfusion conductance - PA average gas pressure (O₂ or CO₂) - Pac gas pressure in air cell - PE gas pressure in respiratory chamber - Pca gas pressure over chorioallantois - perfusion     

Determination of heteronuclear three-bond J-coupling constants in peptides by a simple heteronuclear relayed E.COSY experiment

Summary A simple heteronuclear relayed E.COSY pulse sequence with a minimum number of pulses is proposed for the quantitative determination of heteronuclear three-bond J-coupling constants in uniformly ¹³C-enriched polypeptide samples. Numerous heteronuclear three-bond coupling constants, including , , , and , can be determined for each residue from a single heteronuclear relayed E.COSY spectrum. Couplings relevant for stereospecific assignments as well as for the determination of dihedral angles in the amino acid backbone and in side chains are obtained. The method is demonstrated on the uniformly ¹³C-enriched decapeptide antamanide (-Val¹-Pro²-Pro³-Ala⁴-Phe⁵-Phe⁶-Pro⁷-Pro⁸-Phe⁹-Phe¹⁰-).     

Energetics of the growth of Methanobacterium thermoautotrophicum and Methanococcus thermolithotrophicus on ammonium chloride and dinitrogen

Methanobacterium thermoautotrophicum was grown in continuous culture in a fermenter gassed with H₂ and CO₂ as sole carbon and energy sources, and in a medium which contained either NH₄Cl or gaseous N₂ as nitrogen source. Growth was possible with N₂. Steady states were obtained at various gas flow rates with NH₄Cl and with and the maintenance coefficient varied with the gas input and with the nitrogen source. Growth of Methanococcus thermolithotrophicus in continuous culture in a fermenter gassed with H₂, CO₂ as nitrogen, carbon and energy sources was also examined.Abbreviations molecular growth yield (g dry weight of cells per mol of CH₄ evolved) - growth rate (h^-1) - D dilution rate (h^-1) - rate (h_-1); relation of Neijssel and Tempest and of Stouthamer and Bettenhaussen - energy     

Carbonic anhydrase activity in the blood and the gills of rainbow trout during long-term hypercapnia in hard,bicarbonate-rich freshwater

Summary Carbonic anhydrase (CA) activities in gills and venous blood, acid-base balance, and haematological variables were studied during environmental hypercapnia in rainbow trout (Salmo gairdneri). Batches of 8–10 fish were exposed to about 3 or 13 mmHg in flow-through tests of various duration from 4 h to 80 days.After initial acidosis, blood pH rose above pre-experimental values. At 3 mmHg it became normal again within 21 days, while at 13 mmHg the overshoot lasted for 80 days. In fish acclimated for 3 weeks or more to 13 mmHg , blood HCO ₃ ^– increased four to five times while plasma Cl^– levels were lower and K⁺ higher. Na⁺ levels did not show any consistent trend associated with exposure to hypercapnia. After an initial acidaemia, Hct, Hb, and RBC remained relatively constant.Patterns of change in CA activity differed between gills and erythrocytes. Initially, blood CA decreased at both levels. It then began rising after about 3 weeks and tended to reach pre-experimental values by 80 day's hypercapnia. At 13 mmHg , gill CA increased to twice the pre-experimental level. Compared with blood CA, gill CA appeared to be more specifically involved in fish acclimation to hypercapnia, which demands an increase in blood bicarbonate to provide a sufficient buffering capacity. Increased CA indicates that the gill enzyme may play a more important role than blood CA in acid-base regulation in fish during hypercapnia.Abbreviations CA carbonic anhydrase - Hb haemoglobin - Hct haematocrit value - RBC red blood cells     

Physiology and kinetics of autotrophic denitrification by Thiobacillus denitrificans

Summary A strain of Thiobacillus denitrificans was isolated after enrichment under anaerobic conditions by the continuous culture technique using thiosulfate as energy source and nitrate as electron acceptor and nitrogen source. The isolate was an active denitrifyer, the optimal conditions being 30°C and pH 7.5–8.0. Denitrification was inhibited by sulfate (the reaction product) above 5 g SO ₄ ⁼ /l, whereas high concentrations of the substrates nitrate and thiosulfate were less harmful; nitrite affected denitrification above 0.2 g NO ₂ ^– /l. During the time course of denitrification in a batch culture growth and substrate consumption slowed down already after only half the substrate was utilized due to product inhibition. The following parameters were determined in continuous culture under nitrate limitation: _max=0.11 h^–1, K _S=0.2 mg NO ₃ ^– /l, maximum denitrification rate=0.78 g NO ₃ ^– /g cells·h, g cells/g NO ₃ ^– , g cells/g S₂O ₃ ⁼ . Nitrite did not accumulate during steady state denitrification; the denitrification gas was almost pure N₂. The concentrations of N₂O and NO were below 1 ppm.     

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO₂ production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O₂ saturation reached a minimum which was sustained for 1–3 min before was reached. The LAT correlated with both the (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O₂ desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of , approaching or reaching a minimum saturation at .     

Gas exchange in the incubation mounds of megapode birds

Summary The brush turkey (Alectura lathami) and mallee fowl (Leipoa ocellata) are megapode birds that incubate their eggs by burying them in mounds. Respiratory gas exchange between the buried eggs and the atmosphere occurs mainly by diffusion through about 60 cm of decomposing forest litter (brush turkey) or sand (mallee fowl).Gas fluxes in the brush turkey mound are greatly influenced by the respiration of thermophilic microorganisms which consume O₂ at rates over eight times that of all of the eggs. The respiratory exchange ratio ( ) of the microorganisms is 0.75 and theQ ₁₀ for metabolism is 2.56. Fermentation and nitrogen fixation do not occur in the mounds.If the mound becomes too wet, gas tensions near the eggs can become critical because water increases rates of microbial respiration and impedes gas diffusion. However, field mounds are relatively dry, possibly because the adult bird modifies the shape of the mound and affects the entry of rain water. At egg level in field mounds, and are about 132 and 21 Torr, respectively, in both species. Embryonic respiration decreases and increases about 5 Torr in the immediate environment of individual eggs in late development. Due to a high eggshell gas conductance, which increases during incubation, the gas tensions within the shell of late embryos ( ca. 108 Torr, ca. 47 Torr) are not far from the mean values found in species that nest above ground.