Significant CO2 Effects Research Articles

Inhibition of whole plant respiration by elevated CO2 as modified by growth temperature

Plants of alfalfa (Medicago sativa) and orchard grass (Dactylus glomerata) were grown in controlled environment chambers at two CO2 concentrations (350 and 700 μmol mol‐1) and 4 constant day/night growth temperatures of 15, 20, 25 and 30°C for 50–90 days to determine changes in growth and whole plant CO2 efflux (dark respiration). To facilitate comparisons with other studies, respiration data were expressed on the basis of leaf area, dry weight and protein. Growth at elevated CO2 increased total plant biomass at all temperatures relative to ambient CO2, but the relative enhancement declined (P≤0.05) as temperature increased. Whole plant respiration (Rd) at elevated CO2 declined at 15 and 20°C in D. glomerata on an area, weight or protein basis and in M. sativa on a weight or protein basis when compared to ambient CO2. Separation of Rd into respiration required for growth (Rg) and maintenance (Rm) showed a significant effect of elevated CO2 on both components. Rm was reduced in both species but only at lower temperatures (15°C in M. sativa and 15 and 20°C in D. glomerata). The effect on Rm could not be accounted for by protein content in either species. Rg was also reduced with elevated CO2; however no particular effect of temperature was observed, i. e. Rg was reduced at 20, 25 and 30°C in M. sativa and at 15 and 25°C in D. glomerata. For the two perennial species used in the present study, the data suggest that both Rg and Rm can be reduced by anticipated increases in atmospheric CO2; however, CO2 inhibition of total plant respiration may decline as a function of increasing temperature

Elevated atmospheric CO2 and feedback between carbon and nitrogen cycles

We tested a conceptual model describing the influence of elevated atmospheric CO2 on plant production, soil microorganisms, and the cycling of C and N in the plant-soil system. Our model is based on the observation that in nutrient-poor soils, plants (C3) grown in an elevated CO2 atmosphere often increase production and allocation to belowground structures. We predicted that greater belowground C inputs at elevated CO2 should elicit an increase in soil microbial biomass and increased rates of organic matter turnover and nitrogen availability. We measured photosynthesis, biomass production, and C allocation of Populus grandidentata Michx. grown in nutrient-poor soil for one field season at ambient and twice-ambient (i.e., elevated) atmospheric CO2 concentrations. Plants were grown in a sandy subsurface soil i) at ambient CO2 with no open top chamber, ii) at ambient CO2 in an open top chamber, and iii) at twice-ambient CO2 in an open top chamber. Plants were fertilized with 4.5 g N m−2 over a 47 d period midway through the growing season. Following 152 d of growth, we quantified microbial biomass and the availabilities of C and N in rhizosphere and bulk soil. We tested for a significant CO2 effect on plant growth and soil C and N dynamics by comparing the means of the chambered ambient and chambered elevated CO2 treatments.

Phenology and growth in four annual species grown in ambient and elevated CO2

The objectives of this study were (i) to test the hypothesis that changes in phenology with CO2 are a function of the effect of CO2 upon growth and (ii) to determine if CO2-induced changes in phenology can influence competitive outcome. We examined the effect of 350, 525, and 700 μL∙L−1 CO2 on Guara brachycarpa, Gailardia pulchella, Oenothera laciniata, and Lupinus texensis. Plants were grown as individuals in 150-, 500-, or 1000-mL pots and in competition in 1000-mL pots. Growth and development were monitored at twice-weekly intervals by recording the number of leaves and noting the presence or absence of stem elongation, branching, flower buds, and open flowers. Elevated CO2 affected both growth and phenology, but the direction and magnitude of effects varied with species and soil volume. Elevated CO2 did not appear to affect development through its effect on growth. Those treatments in which there were significant effects of CO2 on growth were generally different from those treatments in which CO2 affected phenology. Rather than affecting phenology by changing plant size, CO2 appeared to affect phenology by modifying the size at which plants switched from one stage to the next. The level of CO2 changed competitive outcome; the importance of Lupinus increased whereas that of Oenothera decreased with increased CO2. These changes were more closely related to the effect of CO2 on growth than its effect on phenology. Key words: time of flowering, size at flowering, competition, photoperiod, rate of development.

Topical Application of CO2 Increases Skin Blood Flow

The topical application of carbon dioxide water to the rat hindpaw produced a concentration-dependent increase of skin blood flow as measured by a laser Doppler flowmeter. About a 100% increase of skin blood flow occurred in response to CO2 when the bath temperature was at 23 degrees C or 34 degrees C, but there was no significant effect of CO2 at 41 degrees C. Carbon dioxide exposure also produced about the same increase of skin blood flow in the acutely or chronically denervated paw as in the control. These findings give experimental support for the clinical use of CO2 bathing in the treatment of disturbances of skin circulation as well as skin ulcers and wounds.

Numerical Evaluation of the Effect of Simultaneous Steam and Carbon Dioxide Injection on the Recovery of Heavy Oil

Summary The immiscible displacement mechanism of CO2 in a simultaneous injection of CO2 and steam in a heavy-oil reservoir is evaluated with a numerical simulation model. In a steam stimulation process, the viscosity reduction effect of CO2 on heavy oil is the major contributor to increased recovery in a high-compressibility reservoir. In a normal-compressibility reservoir, the major benefit is derived from the solution gas effect of the injected CO2. Ignoring the solubility of CO2 in water can introduce an optimistic incremental recovery over steam-only injection. In a steamdrive process, the addition of CO2 to be injected steam improves the final recovery by only a small amount. However, the oil production rate before steam breakthrough appears to be production rate before steam breakthrough appears to be accelerated by the solution of CO2 in the heavy oil. The swelling effect of CO2 does not appear to play an important role in the incremental recovery, because the swelling effect of CO2 at high temperature is small when compared with the thermal expansion of the crude oil. Introduction The growing interest in the application of CO2 injection in EOR schemes has been concentrated so far on the miscible aspect of CO2. The CO2 miscible flood process generally is limited to the recovery of light-gravity process generally is limited to the recovery of light-gravity oil. Application of CO2 miscible flood to heavy-gravity oil has been hampered by the complex phase behavior, including the possible deposition of asphaltene, a solid phase, which could be detrimental to the permeability of phase, which could be detrimental to the permeability of the reservoir. In the immiscible aspect of CO2 injection, the viscosity reduction effect of CO2, generally unimportant in light-oil reservoirs, could play a significant role in the recovery of heavy oil. For all heavy-oil reservoirs, the major mechanism of enhanced recovery methods, which include steam injection and in-situ combustion process, is the reduction of reservoir oil viscosity to allow oil mobilization and to improve the mobility ratio between the reservoir oil and the displacement fluid. A study of the significant viscosity reduction effect of CO2 on high-viscosity crude oil was published as early as 1963. Welker and Dunlop showed that the viscosity reduction could be up to 98 % for a 4,800-cp (4.8-Pas) heavy crude oil at 80 deg. F (27 deg. C) and 800-psi (5515-kPa) carbonation pressure. A proposed field application of CO2 injection was reported to take advantage of this significant viscosity reduction aspect. It was also reported that supercritical CO2 was used to achieve solvent-reduced oil viscosity in some U.S. reservoirs in 1977. A study on the effect of normal reservoir parameters on a CO2 huff ‘n’ puff process was reported parameters on a CO2 huff ‘n’ puff process was reported in 1979. However, no field data have been published. In 1981, the first CO2 cyclic stimulation was conducted in Canada with interesting results. The experiment of solvent addition to steam process has been carried out in the field since probably as early as steam was applied successfully in oil recovery. No systematic evaluation was presented or published. Laboratory physical models were used to evaluate the benefit of solvent addition to steam and the results were reported by Redford. JPT P. 1591

Cat carotid body: oxygen consumption and other parameters.

Cats were anesthetized with pentobarbital, pump ventilated with air, and given heparin, and the carotid body (CB) was vascularly isolated except for the supplying artery. The CB could be normally blood perfused, or alternatively, perfused with Locke's solution; flow of either could be stopped suddenly. Sinus nerve discharge was measured. Tissue oxygen tension (TPO2) in the CB was measured with an O2 microelectrode. Oxygen consumption rates (VO2) calculated from the disappearance curve of O2 during stopped flow were PO2 dependent. When TPO2 was high (100-130 Torr), VO2 (ml.100 g-1.min-1) averaged 1.9 +/- 0.18 (SE) during blood perfusion and either 1.9 +/- 0.1 during perfusion with Locke's solution equilibrated with 25% O2-5% CO2-70% N2 or 1.4 +/- 0.08 when the Locke's solution was equilibrated with air. This significant effect of CO2 could have been due to the delayed onset of sinus nerve discharge when CO2 was not added to the perfusion solution. The number of red blood cells in histological sections from CB frozen during stopped flow of blood was significantly below normal. We concluded that the similarity of the disappearance curves during stopped flow of blood and Locke's solutions was primarily due to the extrusion of red blood cells. In five experiments the broken-off tip of the O2 microelectrode was found in the core of the CB.