The influence of H2, CO2 and dilution rate on the continuous fermentation of acetone-butanol

Summary The effect of product gases, H₂ and CO₂, on solvent production was studied using a continuous culture of alginate-immobilized Clostridium acetobutylicum. Initially, in order to find the optimum dilution rate for aceton--butanol production in this system, fermentations were carried out at various dilution rates. With 10% H₂ and 10% CO₂ in the sparging gas, a dilution rate of 0.07 h^–1 was found to maximize volumetric productivity (0.58 g·l^–1·h^–1), while the maximum specific productivity of 0.27 g^–·h^–1 occured at 0.12 h^–1. Continuous cultures with vigorous sparging of N₂ produced only acids. It was concluded that in the case of continuous fermentation H₂ is essential for good solvent production, although good solvent production is possible in an H₂-absent environment in the case of batch fermentations. When the fermentation was carried out at atmospheric pressure under H₂-enriched conditions, the presence of CO₂ in the sparging gas did not slow down glucose metabolism; rather it changed the direction of the phosphoroclastic reaction and as a result increased the butanol/acetone ratio.     

Activity,milk intake and energy consumption in free-living ringed seal (Phoca hispida) pups

Measurements of growth, activity and energy consumption and estimates of milk intake were made in free-living, nursing ringed seal (Phoca hispida) pups. This was accomplished through the simultaneous use of time-depth recorders and the doubly labelled water technique. The pups spent an average of 52±7% of their time hauled out on the ice, 37±5% of the time in the water at the surface, and 11±5% of the time diving. Average daily mass gain of the pups (n=3) throughout the duration of the study period was 0.35±0.08 kg. The composition of the mass gain was 76% fat, 6% protein and 18% water. The total water flux was measured to be 52±10 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.16 ml·g^-1·h^-1, corresponding to a field metabolic rate of 0.55±0.10 MJ·kg^-1·day^-1, or 3.8±0.6 times the predicted basal metabolic rate based on body size (Kleiber 1975). Average daily milk intake was estimated to be 1379±390 ml. The field metabolic rate for the different components of seal pup activity budgets were calculated to be FMR_{haul out}=1.34 BMR, FMR_surface=6.44 BMR, and FMR_diving=5.88 BMR.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - HTO tritiated water - HT¹⁸O doubly labelled water - RQ respiration quotient - SDA specific dynamic action - TDR time-depth recorder     

Nutrition and burrowing energetics of the Cape mole-rat Georychus capensis

Summary At 22°C the resting oxygen consumption of G. capensis is 1.13±0.05 cm³O₂·g^-1·h^-1 (mean± S.E.). In loose sandy soil the burrowing metabolic rate was approximately three times that of resting (3.41±0.19 cm³O₂·g^-1· h^-1). Rate of oxygen consumption while burrowing bears a linear relationship with rate of burrowing. The equation of the regression line describing this relationship was used to construct a model for calculating energy expenditure of burrowing in free-living mole-rats. The diet of G. capensis consists of some green plant material and geophyte corms. The latter has a mean gross energy content of 16.36 kJ·g^-1 dry weight. The digestibility coefficient for captive G. capensis fed on sweet potato, was 97.42±0.41%. Data collected from an excavated burrow system revealed that the total energetic cost of constructing the burrow amounted to 79% of the estimated digestible energy available from geophyte corms in the area. A food store in the same burrow system was sufficient to meet the maintenance requirements of an adult G. capensis, resting at 22°C, for approximately 80–85 days. Soil samples taken at random adjacent to the burrow contained corms with a mean estimated digestible energy value of 2084 kJ per m³ of soil. A comparison of energetic cost of burrowing and randomly available digestible energy in the field suggests that foraging patterns are not random.     

Net photosynthesis and transpiration of Pinus montana on east and north facing slopes at alpine timberline

Summary Potted Pinus montana seedlings, age 4 years, transplanted on adjacent east and north facing slopes 25 m apart at alpine timberline (2,020 m a.s.l.) were measured for net photosynthesis and transpiration under ambient conditions using climatised Koch-Siemens cuvettes. Concurrent recordings were made of air temperature, atmospheric water vapour pressure deficit and illuminance at each site.On a typical summers day the northern aspect averaged 9% less light, 1.8°C cooler air temperatures and 25% lower v.p.d. levels than the eastern aspect. The order of these differences was found to increase in the autumn. Net photosynthetic rates of seedlings on the northern aspect were on average 28% lower than the rates of seedlings on the warmer eastern aspect. Differences in transpiration rates were even greater with north slope seedlings averaging rates 42% lower than east slope seedlings.Maximum CO₂ uptake rate per hour of east slope seedlings was 3.2 mg CO₂ g^-1 d.w.h^-1 but average rates when light was not limiting were around 2.0 mg CO₂ g^-1 d.w.h^-1. Corresponding values for the north slope seedlings were 3.0 mg CO₂ and 1.8 mg CO₂ g^-1 d.w.h.^-1 respectively.Light intensities below 10 klx, when photosynthesis was strongly limited by light, totalled 48% of available daylight hours on the east slope and more than 50% on the north slope.Net photosynthesis was largely unaffected by air temperature between 10°C and the recorded maximum at either site (24°C east, 20°C north) and there was no apparent response to v.p.d. at levels up to 10 mbar. However the consistently higher net photosynthesis of east slope seedlings under all combinations of weather conditions indicated a possible acclimatisation of seedlings at each site.     

Metabolism and thermoregulation in the eastern hedgehogErinaceus concolor

Body temperature and oxygen consumption were measured in the eastern hedgehog,Erinaceus concolor Martin 1838, during summer at ambient temperatures (T _a) between-6.0 and 35.6°C.E. concolor has a relatively low basal metabolic rate (0.422 ml O₂·g^-1·h^-1), amounting to 80% of that predicted from its body mass (822.7 g). Between 26.5 and 1.2°C, the resting metabolic rate increases with decreasing ambient temperature according to the equation: RMR=1.980-0.057T _a. The minimal heat transfer coefficient (0.057 ml O₂·g^-1·h^-1·°C^-1) is higher than expected in other eutherian mammals, which may result from partial conversion of hair into spines. At lower ambient temperature (from-4.6 to-6.0° C) there is a drop in body temperature (from 35.2 to 31.4° C) and a decrease in oxygen consumption (1.530 ml O₂·g^-1·h^-1) even though the potential thermoregulation capabilities of this species are significantly higher. This is evidenced by the high maximum noradrenaline-induced non-shivering thermogenesis (2.370 ml O₂·g^-1·h^-1), amounting to 124% of the value predicted. The active metabolic rate at ambient temperatures between 31.0 and 14.5° C averages 1.064 ml O₂·g^-1·h^-1; at ambient temperatures between 14.5 and 2.0° C AMR=3.228-0.140T _a.Abbreviations AMR active metabolic rate - bm body mass - BMR basal metabolic rate - h heat transfer coefficient - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum rate of NA-induced non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - STPD standard temperature and pressure (25°C, 1 ATM) - T _a ambient temperature - T _b body temperature     

Use of formate gradients for improving biomass yield of Pichia pinus growing continuously on methanol

Summary Investigations were made into the improvement of growth yield (Y) of Pichia pinus MH 4 growing continuously on methanol by feeding formate so as to create an increasing concentration gradient (transient state). Under particular formate supply conditions, Y could be increased from 0.37 g·g^-1 on methanol alone to 0.55 and 0.47 g·g^-1 in the presence of formate at dilution rates (D) of 0.045 and 0.075 h^-1, respectively. These differences could be explained as being due to a limiting formate consumption rate of 50–60 nmol·min^-1·g^-1 dry wt., coupled to a net-energy generation independent of D. Any further formate oxidation proceeded without energy gain. Deviations from optimum conditions of biomass increase are discussed in terms of different formate oxidizing systems and uncoupling properties of formate itself. These results are compared to and confirmed by steady-state considerations.Abbreviations a steepness of the formate gradient (g·l^-1·h^-1) - a acceleration of change of formate concentration in the fermenter (g·l^-1·h^-2) - D dilution rate (h^-1) - Ft formate - S₁ and S₂ initial and final formate concentration of the gradient (g·l^-1) - Y growth yield in g·g^-1 methanol     

Milk intake,growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence,Canada

In this study we document growth, milk intake and energy consumption in nursing pups of icebreeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactation progresses, and mass transfer efficiency between nursing mothers and pups are also measured. Mass transfer efficiency between mother-pup pairs (n=8) was 42.5±8.4%. Pups were gaining a daily average of 2.0±0.7 kg (n=12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23±8.07 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.20 ml·g^-1·h^-1, which corresponds to a field metabolic rate of 0.55±0.13 MJ·kg^-1·day^-1, or 4.5±0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramatically as lacation progressed. At day 2 of nursing, fat and water content were 39.5±1.9% and 47.3±1.5%, respectively, while the corresponding figures for day 15 were 59.6±3.6% fat and 28.4±2.6% water. Protein content of the milk remained relatively stable during the lactation period with a value of 11.0±0.8% at day 2 and 10.4±0.3% at day 15. Pups drank an average of 3.5±0.9 kg of milk daily, corresponding to a milk intake of 1.75 kg per kg body mass gained. The average daily energy intake of pups was 82.58±19.80 MJ, while the energy built up daily in the tissue averaged 61.72±22.22 MJ. Thus, pups assimilated 74.7% of the energy they received via milk into body tissue. The lactation energetics of ice-breeding grey seals is very similar to that of their land-breeding counterparts.Abbreviations bm body mass - BMR basal metabolic rate - FMR field metabolic rate - IU international unit - RQ respiration quotient - HTO tritiated water - HT¹⁸O doubly labeled water - TBW total body water - VHF very high frequency     

Partitioning of respiration from soil,litter and plants in a mixed-grassland ecosystem

Summary Carbon dioxide effluxes from plants, litter and soil were measured in two mixed-grassland sites in Saskatchewan, Canada. Ecosystems at both locations were dominated by Agropyron dasystachyum (Hook.) Scribn. Respiration rates of intact and experimentally-modified systems were measured in field chambers using alkali-absorption. Removal of green leaves, dead leaves, and litter from a wet sward reduced respiration to as low as 58% of the rate in an intact system. In a dry sward green shoots were the only significant above-ground source of CO₂.Carbon dioxide effluxes from different parts of A. dasystachyum plants, and from soil samples were measured in laboratory vessels at 20° using alkali-absorption. Respiration of green leaves (1.46 mg CO₂ g^-1 h^-1) was significantly higher than microbial respiration in moist, dead leaf samples (0.79 mg CO₂ g^-1 h^-1) or litter (0.75 mg CO₂ g^-1 h^-1). Microbial respiration in air-dried, dead plant material was very low. Average repiration rates of roots separated from soil cores (0.24 mg CO₂ g^-1 h^-1) were lower than many values reported in the literature, probably because the root population sampled included inactive, suberized and senescent roots. Root respiration was estimated to be 17–26% of total CO₂ efflux from intact cores.Laboratory data and field measurements of environmental conditions and plant biomass were combined in order to reconstruct the CO₂ efflux from the shoot-root-soil system. Reconstructed rates were 1.3 to 2.3 times as large as field measured rates, apparently because of stimulation to respiration caused by the experimental manipulations. The standing dead and litter fractions contributed 26% and 23% of the total CO₂ efflux in a wet sward. Both field-measured and reconstructed repiration values suggest that in situ decomposition of standing dead material under moist conditions can be a significant part of carbon balance in mixed grassland.     

Renal function at steady state in a toad (Bufo viridis) acclimated in hyperosmotic NaCl and urea solutions

Kidney function of the euryhaline toad Bufo viridis was studied in animals acclimated to tap water and solutions of NaCl (230 and 500 mosmol · kg^-1 H₂O) and urea (500 mmol · l^-1) in steady-state conditions. An ureter was eatheterized for continuous urine collection and blood was sampled from an iliac artery. A single injection of ³H-inulin served for estimation of glomerular filtration rate: this was in the range of 15–27 ml · kg^-1 · h^-1 and did not differ significantly in any of the acclimation conditions. Urine flow, on the other hand, varied considerably and was highest in tap water (18.2±3.2 ml · kg^-1 · h^-1; urine/plasma inulin ratio=0.88), lower in 230 mosmol · kg^-1 H₂O NaCl solution (13.5±3.9 ml · kg^-1 · h^-1; u/p inulin ratio=1.73) and lowest in 500 mosmol · kg^-1 H₂O NaCl or urea acclimation solutions (5–7 ml · kg^-1 · h^-1; u/p inulin=3.7–4.2). Clearance of free water was high in the tap water group, lower in 230 mosmol · kg^-1 H₂O NaCl solution, and much lower in the hyperosmotic acclimation conditions. Clearances of both Na⁺ and Cl^- were similar under our experimental conditions, but changed independently in accordance to the composition of the acclimation solution. Potassium clearance was similar in all acclimation conditions, and a constant plasma K⁺ concentration was maintained. Urea clearance was high in tap water and 500 mmol · l^-1 urea acclimation groups and low in the NaCl acclimations. The experiments show that the glomerular filtration rate remains more or less unchanged in all acclimation conditions, and suggest that the different rates of urine flow at steady state must be due mostly to tubular processes. The final composition of the urine is the result of specific and highly selective tubular processes.Abbreviations %T fractional reabsorbance - AVT argine vasotocin - C _{free water} free water clearance - C _osmol osmolyte clearance - GFR glomerular filtration rate - MS-222 methanetricaine sulphonate - U/P urine to plasma inulin ratio - V volume     

The energetics of the common mole rat Cryptomyś, a subterranean eusocial rodent from Zambia

Body temperature, oxygen consumption, respiratory and cardiac activity and body mass loss were measured in six females and four males of the subterranean Zambian mole rat Cryptomys sp. (karyotype 2 n=68), at ambient temperatures between 10 and 35°C. Mean body temperature ranged between 36.1 and 33.2°C at ambient temperatures of 32.5–10°C and was lower in females (32.7°C) than in males (33.9°C) at ambient temperatures of 10°C but dit not differ at thermoneutrality (32.5°C). Except for body temperature, mean values of all other parameters were lowest at thermoneutrality. Mean basal oxygen consumption of 0.76 ml O₂·g^-1· h^-1 was significantly lower than expected according to allometric equations and was different in the two sexes (females: 0.82 ml O₂·g^-1·h^-1, males: 0.68 ml O₂·g¹·h^-1) but was not correlated with body mass within the sexes. Basal respiratory rate of 74·min^-1 (females: 66·min¹, males: 87·min^-1) and basal heart rate of 200·min^-1 (females: 190·min^-1, males: 216·min^-1) were almost 30% lower than predicted, and the calculated thermal conductance of 0.144 ml O₂·g^-1·h¹·°C^-1 (females; 0.153 ml O₂·g^-1·h^-1·°C^-1, males: 0.131 ml O₂·g^-1·h^-1·°C^-1) was significantly higher than expected. The body mass loss in resting mole rats of 8.6–14.1%·day^-1 was high and in percentages higher in females than in males. Oxygen consumption and body mass loss as well as respiratory and cardiac activity increased at higher and lower than thermoneutral temperatures. The regulatory increase in O₂ demand below thermoneutrality was mainly saturated by increasing tidal volume but at ambient temperatures <15°C, the additional oxygen consumption was regulated by increasing frequency with slightly decreasing tidal volume. Likewise, the additional blood transport capacity was mainly effected by an increasing stroke volume while there was only a slight increase of heart frequency. In an additional field study, temperatures and humidity in different burrow systems have been determined and compared to environmental conditions above ground. Constant temperatures in the nest area 70 cm below ground between 26 and 28°C facilitate low resting metabolic rates, and high relative humidity minimizes evaporative water loss but both cause thermoregulatory problems such as overheating while digging. In 13–16 cm deep foraging tunnels, temperature fluctuations were higher following the above ground fluctuations with a time lag. Dominant breeding females had remarkably low body temperatures of 31.5–32.3°C at ambient temperatures of 20°C and appeared to be torpid. This reversible hypothermy and particular social structure involving division of labour are discussed as a strategy reducing energy expenditure in these eusocial subterranean animals with high foraging costs.Abbreviations BMR basal metabolic rate - br breath - C thermal conductance - HR neart rate - LD light/dark - M _b body mass - MR metabolic rate - OP oxygen pulse - PCO₂ partial pressure of carbon dioxide - PO₂ partial pressure of oxygen - RMR resting metabolic rate - RR respiratory rate - T _a ambient temperature - T _b body temperature - TNZ thermal neural zone - O₂ oxygen consumption     

Morphological and physiological adaptive traits of Mediterranean narrow endemic plants: The case of Centaurea gymnocarpa (Capraia Island,Italy)

A case study on Centaurea gymnocarpa Moris & De Not., a narrow endemic species, was carried out by analyzing its morphological, anatomical, and physiological traits in response to natural habitat stress factors under Mediterranean climate conditions. The results underline that the species is particularly adapted to the environment where it naturally grows. At the plant level, the above-ground/below-ground dry mass (1.73 ± 0.60) shows its investment predominately in the above-ground structure with a resulting total leaf area per plant of 1399 ± 94 cm². The senescent attached leaves at the base of the plant contribute to limit leaf transpiration by shading soil around the plant. Moreover, the dense C. gymnocarpa leaf pubescence, leaf rolling, the relatively high leaf mass area (LMA = 12.3 ± 1.3 mg cm⁻²) and leaf tissue density (LTD = 427 ± 44 mg cm⁻³) contribute to limit leaf transpiration, also postponing leaf death under dry conditions. At the physiological level, a relatively low respiration/photosynthesis ratio (R/P_N) in spring results from high R [2.26 ± 0.59 μmol (CO₂) m⁻² s⁻¹] and P_N [12.3 ± 1.5 μmol (CO₂) m⁻² s⁻¹]. The high photosynthetic nitrogen use efficiency [PNUE = 15.5 ± 0.4 μmol (CO₂) g⁻¹ (N) s⁻¹] shows the large amount of nitrogen (N) invested in the photosynthetic machinery of new leaves, associated to a high chlorophyll content (Chl = 35 ± 5 SPAD units). On the contrary, the highest R/P_N ratio (1.75 ± 0.19) in summer is due to a significant P_N decrease and increase of R in response to drought. The low PNUE [1.5 ± 0.2 μmol (CO₂) g⁻¹ (N) s⁻¹] in this season is indicative of a greater N investment in leaf cell walls which may contribute to limit transpiration. On the contrary, the low R/P_N ratio (0.05 ± 0.02) in winter is resulting from the limited enzyme activity of the respiratory apparatus [R = 0.23 ± 0.08 μmol (CO₂) m⁻² s⁻¹] while the low PNUE [3.5 ± 0.2 μmol (CO₂) g⁻¹ (N) s⁻¹] suggests that low temperatures additionally limit plant production. The experiment of the imposed water stress confirms that the C. gymnocarpa growth capability is in conformity with the severe conditions of its natural habitat, likewise as it may be the case with others narrow endemic species that have occupied niches with similar extreme conditions.     

Influence of rain,tidal wetting and relative humidity on release of carbon dioxide by standing-dead salt-marsh plants

Summary Dead parts of salt-marsh plants form a considerable fraction of their annual average standing crop. A microbial assemblage living on and in the standing-dead leaves and stems of Spartina alterniflora and Juncus roemerianus responds to saltwater, freshwater or water-vapor wetting by immediately beginning to release CO₂. Water-saturated, standing-dead leaves and culms of S. alterniflora release CO₂ at steady rates of as much as about 200 and 140 g CO₂–C·g^-1 dry·h^-1, respectively, at temperatures of 25–30°C, after an initial burst of higher rates. These CO₂-release rates are within the range of maximal rates reported for decaying terrestrial litter, and are as high as most rates reported for S. alterniflora decaying under continuously wetted or submerged conditions.     

CO2 gas exchange of the understory plantAsarum europaeum L. in November

The CO₂ gas exchange rates of the Central European perennial understory plantAsarum europaeum L. were measured in late autumn (October 30 to November 30) in its natural habitat day and night.During these measurements the temperature ranged from 0 to 15°C and the absolute air humidity from 3 to 10 mg H₂O·1^–1. Temperature and absolute air humidity over these ranges did not affect CO₂ net assimilation which was determined almost entirely by quantum flux density.CO₂ net assimilation was light saturated at about 100 M·m^–2·s^–1 quantum flux density. The uptake rate at this point was 4.3 mg·dm^–2·h^–1. The compensation point occurred at approximately 1 M·m^–2·s^–1.     

Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Summary Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O₂ uptake was low at 81 l O₂·g^–1·h^–1±19.0 (SD) at 25°C increasing to 253.5 l O₂·g^–1·h^–1±94.8 (SD) at 40°C giving aQ ₁₀ value of 2.1. Skin O₂ uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.Blood O₂ affinity was low with aP ₅₀ of 47.5 mmHg at 25°C and pH 7.65. Then _H-value at 25°C increased from 2.7 aroundP ₅₀ to 5.0 at O₂ saturations exceeding 70–80%. Surprisingly, blood O₂ affinity was nearly insensitive to temperature expressed by a H value of ±1.0 kcal·mole between 25 and 40°C.The adaptive significance of the low O₂ affinity, the increase ofn _H with O₂ saturation and the temperature insensitive O₂-Hb binding is discussed in relation to the high and fluctuating body temperatures ofChiromantis.     

Effects of CO2 enrichment and water stress on gas exchange of Liquidambar styraciflua and Pinus taeda seedlings grown under different irradiance levels

Summary The effects of CO₂ enrichment and water stress on gas exchange of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) seedlings were examined for individuals grown from seed under high (1000 mol·m^-2·s^-1) and low (250 mol·m^-2·s^-1) photosynthetic photon flux density at 350, 675 and 1000 l·l^-1 CO₂. At 8 weeks of age, half the seedlings in each CO₂-irradiance treatment were subjected to a drying cycle which reduced plant water potential to about -2.5 MPa in the most stressed plants, while control plants remained well-watered (water potentials of -0.3 and -0.7 MPa for sweetgum and loblolly pine, respectively). During this stress cycle, whole seedling net photosynthesis, transpiration and stomatal conductance of plants from each CO₂-irradiance-water treatment were measured under respective growth conditions.For both species, water stress effects on gas exchange were greatest under high irradiance conditions. Waterstressed plants had significantly lower photosynthesis rates than well-watered controls throughout most of the drying cycle, with the most severe inhibition occurring for low CO₂, high irradiance-grown sweetgum seedlings. Carbon dioxide enrichment had little effect on gas exchange rates of either water-stressed or well-watered loblolly pine seedlings. In contrast, water stress effects were delayed for sweetgum seedlings grown at elevated CO₂, particularly in the 1000 l·l^-1 CO₂, high irradiance treatment where net photosynthesis, transpiration and conductance of stressed plants were 60, 36 and 33% of respective control values at the end of the drying cycle. Development of internal plant water deficits was slower for stressed sweetgum seedlings grown at elevated CO₂. As a result, these seedlings maintained higher photosynthetic rates over the drying cycle than stressed sweetgum seedlings grown at 350 l·l^-1 CO₂ and stressed loblolly pine seedlings grown at ambient and enriched CO₂ levels. In addition, water-stressed sweetgum seedlings grown at elevated CO₂ exhibited a substantial increase in water use efficiency.The results suggest that with the future increase in atmospheric CO₂ concentration, sweetgum seedlings should tolerate longer exposure to low soil moisture, resulting in greater first year survival of seedlings on drier sites of abandoned fields in the North Carolina piedmont.     

Comparative ecophysiology of the chromosome races in Viola adunca J.E. Smith

Summary Comparisons of net CO₂ assimilation, dark respiration, leaf resistance, and leaf water potential were made between diploid and polyploid races of Viola adunca from the Cypress Hills, Alberta, Canada. The mean maximum net CO₂ assimilation rate, at 20 C and 500 E m^-2 s^-1 (phAR) was 26 mg CO₂ g^-1 h^-1 (12 mg CO₂ dm^-2 h^-1) for polyploids, and 23 mg CO₂ g^-1 h^-1 (11 mg dm^-2 h^-1) for diploids. The difference is not statistically significant. Net CO₂ assimilation rates at low (0° C) and high (40° C) temperatures were virtually the same for diploids and polyploids. There were no statistically significant differences between the chromosome races in light compensation or light saturation over the 0° to 40° C temperature range studied. Average dark respiration of the polyploid race at 20 C was 2.2 mg CO₂ g^-1 h^-1 (1.0 mg CO₂ dm^-2 h^-1) compared with 2.0 mg CO₂ g^-1 h^-1 (0.95 mg CO₂ dm^-2 h^-1) for the diploid race. The mean maximum leaf water potential of well watered plants was-7.9 bars for both ploidy levels. Minimum leaf resistance was ca. 3.6 s cm^-1 for both ploidy levels. Maximum net CO₂ assimilation rates in both ploidy levels occurred at-9 bars leaf water potential. Based upon the plant responses studied, there are no differences between chromosome races collected from the same general area, and the polyploids do not respond more favorably to extremes of temperature and water potential. Ploidy per se does not affect the response of Viola adunca to its environment in this particular case.     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Photosynthetic recovery in the resurrection plant Selaginella lepidophylla after wetting

Summary Photosynthetic recovery (PR) in a southwest Texas, USA population of Selaginella lepidophylla (Hook and Grev.) (Selaginellaceae), a poikilohydric spikemoss, was examined in the laboratory. Infrared CO₂ gas analysis and ribulose 1,5-bisphosphate (RuBP) carboxylase activity measurements indicated that optimal temperature for PR was near 25°C in terms of: (1) rapidity of net CO₂ uptake after hydration (5.4 h), (2) maximum net photosynthetic rate at 2000 E·m^-2·s^-1 (2.44 mg CO₂·g(DWT)^-1·h^-1), and (3) maximum net CO₂ assimilation per 30 h hydration event (43.8 mg CO₂·g(DWT)^-1·30 h^-1). The PR was much slower at both 15° and 35° C, with lower photosynthetic rates and net carbon gains per hydration event. High respiratory costs were incurred at 45°C and no net photosynthesis was observed. Increases in RuBP carboxylase activity and chlorophyll content during 24 h hydration were also greatest near 25°C. Dry plants had 60% of the enzyme activity of fully recovered (24 h hydration) plants, indicating enzyme conservation. Actinomycin D and cycloheximide did not appear to inhibit PR, but chloramphenicol appeared to totally inhibit RuBP carboxylase activity increases over levels conserved in dry plants. Therefore, rapid PR in S. lepidophylla was achieved by both rapid increase in RuBP carboxylase activity, possibly via de novo synthesis, and conservation of the photosynthetic enzyme. Both mechanisms are essential to maximize assimilation in S. lepidophylla in an environment where hydrated periods are rare and of short duration.     

CO2 exchange in the Empetrum nigrum-Sphagnum fuscum community

Summary The CO₂ exchange of the Empetrum nigrum-Sphagnum fuscum community of a raised bog was studied in the laboratory at different temperature (from 5 to 30° C) and irradiance (up to 128 W m^-2) combinations during one growing season. The total CO₂ exchange was divided into three components, namely those due to Empetrum nigrum, Sphagnum fuscum, and peat, respectively. At the optimum temperature (10 to 15° C) the maximum net CO₂ exchange of Empetrum nigrum was c. 200 and that of Sphagnum fuscum c. 250 mg CO₂ m^-2h^-1. The total respiration in peat increased exponentially from 50 to 350 mg CO₂ m^-2h^-1 with increasing temperature from 5 to 30° C. About 40% of the CO₂ fixed by the community in optimal temperature and irradiation conditions was released immediately.     

The effect of carbonic anhydrase inhibitors on secretion by the parotid and mandibular glands of red kangaroos Macropus rufus

Summary The effects of carbonic anhydrase inhibitors on secretion by macropodine parotid and mandibular glands were investigated using anaesthetized red kangaroos. In the parotid gland, acetazolamide (500 mol·l^-1) reduced a stable acetylcholine-evoked, half-maximal flow rate of 2.02±0.034 to 0.27±0.023 ml·min^-1 (87% reduction). Concurrently, salivary bicarbonate concentration and secretion fell (129.4±1.46 to 80.9±1.63 mmol·l^-1 and 264.8±7.96 to 22.3±2.30 mol·min^-1, respectively), phosphate and chloride concentrations rose (14.0±0.79 to 27.6±0.85 mmol·l^-1 and 5.6±0.25 to 27.5±1.32 mmol·l^-1, respectively), sodium concentration and osmolality were unaltered, and potassium concentration fell (8.8±0.33 to 6.4±0.29 mmol·l^-1). High-rate cholinergic stimulation during acetazolamide blockade was unable to increase salivary flow beyond 11±0.9% of that for equivalent unblocked control stimulation. However, superimposition of isoprenaline infusion on the acetylcholine stimulation caused a three-fold increase in the blocked flow rate. These treatments were accompanied by small increases in salivary phosphate and chloride concentrations but not bicarbonate concentration. Methazolamide infusion caused similar changes in parotid secretion. In the mandibular gland, acetazolamide infusion had no effect on salivary flow rate during either low- or high-level acetylcholine stimulation. Acetazolamide caused no alterrations in salivary electrolyte secretion at low flow rates, but curtailed the rise in bicarbonate concentration associated with high-level acetylcholine stimulation. Acetazolamide administration did not affect the increase in salivary flow rate associated with isoprenaline infusion, but did block the concomitant increase in bicarbonate concentration and secretion substantially. It was concluded that neither cholinergic nor adrenergic stimulation of mandibular fluid secretion depends on secretion of bicarbonate derived from catalysed hydration of CO₂, but a substantial proportion of the increase in bicarbonate secretion during isoprenaline administration, which is probably ductal in origin, is so dependent. In contrast to other salivary glands, including the ovine parotid, fluid secretion by the kangaroo parotid gland during cholinergic stimulation is largely dependent (about 90%) on secretion of bicarbonate derived from hydration of CO₂ catalysed by glandular carbonic anhydrase. Fluid secretion during adrenergic stimulation is not bicarbonate dependent.Abbreviations b.w. body weight - PAH p-aminohippurate - PCO₂ partial pressure carbon dioxide - PCO₂ partial pressure of oxygen