ASSIMILATION AND RESPIRATION OF EXCISED LEAVES AT HIGH CONCENTRATIONS OF CARBON DIOXIDE

Characteristics of the large-scale circulation during episodes with high and low concentrations of carbon dioxide and air pollutants at an arctic monitoring site in winter

New study on the correlation between carbon dioxide concentration in the environment and radon monitor devices

Spontaneous electroencephalograms (EEG) and somatosensory evoked potentials (SEPS) were recorded in turkeys while they were kept in an atmosphere of either 49 or 86 per cent carbon dioxide in air. The time to the loss of SEPS was not related to the concentration of carbon dioxide, but the time to the onset of an isoelectric EEG was shorter at the higher concentration of carbon dioxide. In comparison with other gas stunning methods it was considered that stunning with these high concentrations of carbon dioxide would not have any welfare advantages over stunning in argon with 2 per cent residual oxygen or in a mixture of 30 per cent carbon dioxide and 60 per cent argon in air.

Permeation properties were analyzed for a mixture of CO2, O2, and N2 in a medium-size polysulfone hollow fiber permeator with a net permeation area of 4.22 m2. Measurements were conducted as a function of feed composition, reject flow rate, and feed pressure. Results included variations in species permeability, separation factor, permeate enrichment, reject depletion, and stage cut as a function of system parameters. Variations in permeation properties show strong dependence on feed composition, reject flow rate, and feed pressure. Permeability of carbon dioxide was higher at larger feed pressures and higher carbon dioxide content in the feed stream. Effect of increasing the reject flow rates on the permeability of carbon dioxide was affected by the system pressure and the carbon dioxide content in the feed stream. At low pressures, increase of the reject flow rate resulted in a decrease of carbon dioxide permeability. The opposite behavior was obtained at higher feed pressures. Increase of the reject flow rate reduced the gas residence time within the permeator. Increase of reject flow rate reduced species residence within the permeator and in turn increased resistance to species transport within the permeator. However, higher system pressures and carbon dioxide content in the feed stream resulted in larger levels of membrane plasticization, which increased the permeation rates of all species. The combined efféct of reducing the species residence time within the permeator and the level of membrane plasticization favored the permeation of carbon dioxide versus the other two species. Variations in other permeation properties, which include oxygen and nitrogen permeabilities, stage cut, permeate enrichment in carbon dioxide, and reject depletion in carbon dioxide, were also explained in terms of resistances encountered within the permeator and the membrane.

Lactic acid, carbon dioxide and human sweat stimuli were presented singly and in combination to femaleAedes aegypti(Linnaeus) within a wind-tunnel system. The take-off, flight, landing and probing responses of the mosquitoes were recorded using direct observation and video techniques. The analyses determined the nature of the response to different stimuli and the concentration ranges within which specific behaviours occurred. A threshold carbon dioxide concentration for taking-off of approximately 0.03% above ambient was detected. Lactic acid and human sweat samples did not elicit take-off when presented alone, however, when they were combined with elevated carbon dioxide, take-off rate was enhanced in most of the combinations tested. Flight activity was positively correlated with carbon dioxide level and some evidence for synergism with lactic acid was found within a narrow window of blend concentrations. The factors eliciting landing were more subtle. There was a positive correlation between landing rate and carbon dioxide concentration. At the lowest carbon dioxide concentration tested, landing occurred only in the presence of lactic acid. Within a window of low to intermediate concentrations, landing rate was enhanced by this combination. At the highest carbon dioxide concentration, landing was however inhibited by the presence of lactic acid. The sweat extract elicited landings in the absence of elevated carbon dioxide. This indicated the presence of chemical stimuli, other than lactic acid, active in the short range. Probing occurred only at low carbon dioxide concentrations and there was no probing when lactic acid alone was tested. There was however probing in the presence of combined stimuli, the level of response seemed to be positively correlated with the ratio of carbon dioxide and lactic acid concentrations.

Welfare implications of gas stunning pigs: 3. the time toloss of somatosensory evoked potential and spontaneous electrocorticogram of pigs during exposure to gases

STUDIES IN THE PHYSIOLOGY OF SPERMATOZOA

Electrical waterbath stunning is the most common method used to stun poultry under commercial conditions. The voltage supplied to a multiple bird waterbath stunner must be adequate to deliver the required minimum current to each bird. High frequency (> 300 Hz) electrical waterbath stunning needs further investigation to determine its efficiency. It should always be followed by a prompt neck cutting procedure where all the major blood vessels in the neck are severed. Irrespective of the waveform or frequency of the currents employed, constant current stunners should be installed under commercial conditions to ensure that the minimum currents are delivered to individual birds in waterbath stunners. Head only electrical stunning of poultry is being investigated in detail and there is scope for commercial development. Important features include (a) a constant current capable of delivering a preset current, (b) a bird restraining conveyor and head presentation devices enabling the stunning tongs to be accurately placed, (c) more effective electrical stunning tongs in terms of delivering necessary currents while using low voltages, and (d) induction of cardiac arrest immediately after stunning to eliminate wing flapping. Stunning/killing of poultry still in their transport containers using gas mixtures would appear to be the best future option as far as bird welfare is concerned. However, birds can also be stunned/killed on a conveyor using gas mixtures, thereby eliminating the stress associated with the shackling of live birds before electrical stunning. Under the conveyor system birds should be presented to the gas mixtures in a single layer. Within gas mixtures a minimum of 90% argon in air would appear to be the first choice. A mixture of 30% carbon dioxide and 60% argon in air is better than using a high concentration of carbon dioxide in air, and is therefore considered to be the second choice. A two stage system that involves firstly stunning broilers with a low concentration of carbon dioxide and then killing them with a high concentration of carbon dioxide can be used by those who wish to use this gas for economic reasons. The two stages should be distinctly separated so that the birds are stunned well before exposure to a high concentration of carbon dioxide in air. In comparison with carbon dioxide alone, a mixture of 30% oxygen and 40% carbon dioxide in air prolongs the induction of anaesthesia and the exposure time required to kill the birds. The addition of oxygen to carbon dioxide may therefore not have any benefit to bird welfare or the processors. Mechanical stunning of poultry using penetrating captive bolts or non-penetrating mushroom headed bolts has been developed. However, stunning with these devices results in very severe wing flapping and further research is necessary to find ways of alleviating this problem.

Distribution of methane and carbon dioxide concentrations in the near-surface zone and their genetic characterization at the abandoned “Nowa Ruda” coal mine (Lower Silesian Coal Basin, SW Poland)

Natural gas dehydration by molecular sieve in offshore plants: Impact of increasing carbon dioxide content

S OME of the earliest studies in photosynthesis were concerned with the relation of the assimilatory activity of green plants to the carbon dioxide concentrations of their environments. Although these were made at a time when the importance of the interaction of factors determining the rate was not understood, it was established that with increasing concentration of carbon dioxide the rate of assimilation rose to a maximum and then declined. The focus of interest was the establishment of 'optima'. The optimal concentration varied for different species. While Godlewski (I873), Kreusler (I885) and others showed that the concentration above which assimilatory activity declined was about 7-IO %, other estimates were as high as 20 0. It has generally been assumed that a concentration of carbon dioxide of from 4 to 5 %0 is distinctly lower than that causing a decline in activity. Willstatter & Stoll (I9I8) performed the great majority of their large range of experiments in air streams containing concentrations of 4-6 %0, and many modern workers have followed their methods. Apart from the known effects of very high concentrations of carbon dioxide upon stomatal aperture, the possible causes of the decline of assimilation rate when the 'optimal' concentration of carbon dioxide is exceeded have been incompletely understood and are usually referred to in vague terms. Thus Blackman (I905) says: 'Ultimately, if the supply of carbon dioxide in the air current be increased up to 30, 50, 70 %0, the carbon dioxide will have a general depressing effect on the whole vitality, and before suspension of all function a diminution of assimilation undoubtedly occurs. This is, however, quite a separate process.' Both Stiles (I925,

Responses of Respiration to Increases in Carbon Dioxide Concentration and Temperature in Three Soybean Cultivars

The recent elevation and predicted future rise in atmospheric carbon dioxide concentrations has led to greater interest in the effects of higher carbon dioxide concentrations on crop plants. Whilst there is a relatively large amount of information on the effects of increased carbon dioxide concentration on arable and glasshouse crops, relatively little is known about the responses of cool temperature forage crops to greater carbon dioxide concentrations. One of the most important forage crops is Lolium whose responses to higher carbon dioxide concentration have been de scribed at the whole crop level (Nijs, Impens & Behaeghe 1988, 1989; Hardacre, Lang & Christeller 1986). However, there is little information on the physiology behind the observed crop re sponses, particularly on how the plant acclimates to higher carbon dioxide concentrations. Thus we determined the effect of increased carbon dioxide and transfers from ‘ambient’ to ‘high’ carbon dioxide concentrations on growth and some physiological characters of Lolium temulentum.

Alfalfa (Medicago sativa L.) and orchard grass (Dactylis glomerata L.) plots were exposed to ambient or ambient plus 350 cm3 m-3 carbon dioxide concentrations at Beltsville, Maryland, U.S.A. Replicate plots were established in different years and fertilized annually. We report here data for the second and third years after establishment. There has been no increase in the yearly production of either species at the elevated carbon dioxide concentration after the first sea- son. In orchard grass, reduced growth at the high carbon dioxide concentration in the spring offset growth stimulation in the summer. Weed growth was consistently increased by carbon dioxide enrichment, but weed species composition was unaffected. Leaf photosynthetic capacity was reduced by the high carbon dioxide concentration in both crop species, as was leaf nitrogen content. Canopy carbon dioxide uptake was slightly higher in the elevated carbon dioxide treatments, consistent with the increased weed growth. In alfalfa, elevated carbon dioxide significantly reduced canopy carbon dioxide

PREVIOUS investigations of the relationship in Chlorella between rate of photosynthesis at high light intensities and concentration of carbon dioxide have been made using cells suspended in alkaline solutions1. In such solutions cells grown in 4 per cent carbon dioxide show an unusually long induction phase (t½, 40–50 min.) at low concentrations of carbon dioxide; but when allowance is made for this and the rate of photosynthesis in the steady state alone considered, half the maximum rate is attained with a concentration of carbon dioxide2 of 0.9 × 10−6 M at 25° C. The possibility has been suggested that in alkaline solution the relatively high concentration of bicarbonate ion affects the rate of photosynthesis3.