Effect of the vibrational excitation of CO molecules on the parameters of an RF discharge

A one-dimensional model of an RF discharge in CO-containing gas mixtures is developed. The model takes into account the effect of the degree of vibrational excitation of CO molecules on the structure of the discharge and on its parameters. Experimental data are presented from measurements of the voltage-power characteristics of RF discharges in gas mixtures with different CO contents in the pressure range of 10–100 torr. The model developed is used to calculate the dependence of the root-mean-square discharge voltage on the specific power deposition in an RF discharge under our experimental conditions. The experimental data are compared to the results of numerical simulations. For working gas pressures of about 100 torr, which are typical of the operation of slab CO lasers, the calculated voltage-power characteristics of an RF discharge agree satisfactorily with those obtained experimentally. The theoretical model predicts that the vibrational excitation of CO molecules leads to a redistribution of the RF field in the discharge gap and to an increase in the laser efficiency.     

Balance of CO molecules in the plasma of a sealed-off CO laser

Abstrac The processes of dissociation and recombination of CO molecules in the plasmas of discharges in He/CO and He/CO/Xe mixtures under conditions characteristic of sealed-off CO lasers are investigated. The concentrations of CO molecules and the main products of their dissociation—O and C atoms and CO₂ molecules—are measured simultaneously for the first time, and the time evolution of the initial working mixture composition in the discharge is calculated. It is shown that the main channel for the regeneration of CO molecules in a sealed-off discharge is the heterogeneous recombination of C and O atoms. The rate constants for this process are estimated. __________ Translated from Fizika Plazmy, Vol. 30, No. 9, 2004, pp. 845–854. Original Russian Text Copyright ? 2004 by Grigorian, Kochetov.     

Recent observations of interstellar molecules: Detection of CCO and a limit on H2C3O

In order to test gas-phase reaction schemes for the production of small oxides of carbon in cold, dense interstellar clouds, we have searched for the radical CCO and for propadienone (H₂C₃O) in Taurus Molecular Cloud 1, a nearby cloud which exhibits a rich organic chemistry. The radical CCO has been detected with a fractional abundance some two orders of magnitude less than that of CCS, about one order of magnitude less than that of H₂CCO, and slightly less than that of C₃O. An upper limit has been obtained on the abundance of propadienone which is slightly less than that of its isomer propynal (HC₂CHO).     

Structure and function of LCI1: a plasma membrane CO2 channel in the Chlamydomonas CO2 concentrating mechanism

Microalgae and cyanobacteria contribute roughly half of the global photosynthetic carbon assimilation. Faced with limited access to CO₂ in aquatic environments, which can vary daily or hourly, these microorganisms have evolved use of an efficient CO₂ concentrating mechanism (CCM) to accumulate high internal concentrations of inorganic carbon (C_i) to maintain photosynthetic performance. For eukaryotic algae, a combination of molecular, genetic and physiological studies using the model organism Chlamydomonas reinhardtii, have revealed the function and molecular characteristics of many CCM components, including active C_i uptake systems. Fundamental to eukaryotic C_i uptake systems are C_i transporters/channels located in membranes of various cell compartments, which together facilitate the movement of C_i from the environment into the chloroplast, where primary CO₂ assimilation occurs. Two putative plasma membrane C_i transporters, HLA3 and LCI1, are reportedly involved in active C_i uptake. Based on previous studies, HLA3 clearly plays a meaningful role in HCO₃^? transport, but the function of LCI1 has not yet been thoroughly investigated so remains somewhat obscure. Here we report a crystal structure of the full‐length LCI1 membrane protein to reveal LCI1 structural characteristics, as well as in vivo physiological studies in an LCI1 loss‐of‐function mutant to reveal the C_i species preference for LCI1. Together, these new studies demonstrate LCI1 plays an important role in active CO₂ uptake and that LCI1 likely functions as a plasma membrane CO₂ channel, possibly a gated channel.     

CO2和O3浓度倍增及其复合作用对大豆叶绿素含量的影响

利用开顶箱(OTC)法研究了在CO2和O3浓度倍增及其复合作用下,大豆叶片叶绿素含量及叶绿素a／b值的变化规律。结果表明,不同生育时期大豆叶片中叶绿素含量不同,Chla、Chlb和ChlT都表现出低．高一低的趋势,而且不同处理间变化不同步。不同处理间比较,O3处理的植株叶绿素含量下降最为明显,其次是复合处理的影响,而CO2浓度倍增对提高叶片叶绿素含量有一定的作用。Chla/b呈下降趋势,受CO2倍增影响最明显,有利于提高作物的光合性能。     

Effect of Elevated CO2 on Stomatal Density and Distribution in a C4 Grass and a C3 Forb under Field Conditions

Two common tallgrass prairie species, Andropogon gerardii, thedominant C₄ grass in this North American grassland, and Salviapitcheri, a C₃ forb, were exposed to ambient and elevated (twiceambient) CO₂ within open-top chambers throughout the 1993 growingseason. After full canopy development, stomatal density on abaxialand adaxial surfaces, guard cell length and specific leaf mass(SLM; mg cm^-2) were determined for plants in the chambers aswell as in adjacent unchambered plots. Record high rainfallamounts during the 1993 growing season minimized water stressin these plants (leaf xylem pressure potential was usually >-1·5 MPa in A. gerardii) and also minimized differencesin water status among treatments. In A. gerardii, stomatal densitywas significantly higher (190 ± 7 mm^-2; mean ±s.e.) in plants grown outside of the chambers compared to plantsthat developed inside the ambient CO₂ chambers (161 ±5 mm^-2). Thus, there was a significant 'chamber effect' on stomataldensity. At elevated levels of CO₂, stomatal density was evenlower (P < 0·05; 121 ± 5 mm^-2). Most stomatawere on abaxial leaf surfaces in this grass, but the ratio ofadaxial to abaxial stomatal density was greater at elevatedlevels of CO₂. In S. pitcheri, stomatal density was also significantlylower when plants were grown in the open-top chambers (235 ±10 mm^-2 outside vs. 140 ± 6 mm^-2 in the ambient CO₂ chamber).However, stomatal density was greater at elevated CO₂ (218 ±12 mm^-2) compared to plants from the ambient CO₂ chamber. Theratio of stomata on adaxial vs. abaxial surfaces did not varysignificantly in this herb. Guard cell lengths were not significantlyaffected by growth in the chambers or by elevated CO₂ for eitherspecies. Growth within the chambers resulted in lower SLM inS. pitcheri, but CO₂ concentration had no effect. In A. gerardii,SLM was lower at elevated CO₂. These results indicate that stomataland leaf responses to elevated CO₂ are species specific, andreinforce the need to assess chamber effects along with treatmenteffects (CO₂) when using open-top chambers.Copyright 1994, 1999Academic Press Andropogon gerardii, elevated CO₂, Salvia pitcheri, stomatal density, tallgrass prairie     

Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

CO2 and O2 dependence of PS II activity in C4 plants having genetically produced deficiencies in the C3 or C4 cycle

The CO2 dependence of rates of CO2 fixation (A) and photochemistry of PS II at 5, 15 and 30% O2 were analyzed in the C4 plant Amaranthus edulis having a C4 cycle deficiency [phosphoenolpyruvate carboxylase (PEPC) mutants], and in the C4 plant Flaveria bidentis having a C3 cycle deficiency [Rubisco small subunit antisense (SSU)]. In the wild type (WT) A. edulis and its heterozygous mutant having less than 50% WT PEPC activity there was a similar dependence of A and PS II photochemistry on varying CO2, although the CO2 saturated rates were 25% lower in heterozygous plants. The homozygous plants having less than 2% PEPC of the WT had significant levels of photorespiration at ambient levels of CO2 and required about 30 times ambient levels for maximum rates of A. Despite variation in the capacity of the C4 cycle, more than 91% of PS II activity was linearly associated with A under varying CO2 at 5, 15 and 30% O2. However, the WT plant had a higher PS II activity per CO2 fixed under saturating CO2 than the homozygous mutant, which is suggested to be due to elimination of the C4 cycle and its associated requirement for ATP from a Mehler reaction. In the SSU F. bidentis plants, a decreased rate of A (35%) and PS II activity (33%) accompanied a decrease in Rubisco capacity. There was some increase in alternative electron sinks at high CO2 when the C3 cycle was constrained, which may be due to increased flux through the C4 cycle via an ATP generating Mehler reaction. Nevertheless, even with constraints on the function of the C4 or C3 cycle by genetic modifications, analyses of CO2 response curves under varying levels of O2 indicate that CO2 assimilation is the main determinant of PS II activity in C4 plants.     

Effect of O2 and CO2 on net CO2 exchange in a high-CO2-requiring mutant of Chlamydomonas reinhardtii during dark-light-dark transitions

Net CO₂ exchange was monitored through a dark-light-dark transition, under 2% and 21% O₂ in the presence and absence of CO₂, in Chlamydomonas reinhardtii wild type and the high-CO₂-requiring mutant ca-1-12-1C. Upon illumination at 350 l/l CO₂, ca-1-12-1C cell exhibited a large decrease in net CO₂ uptake following an initial surge of CO₂ uptake. Net CO₂ uptake subsequently attained a steady-state rate substantially lower than the maximum. A large, O₂-enchanced post-illumination burst of CO₂ efflux was observed after a 10-min illumination period, corresponding to a minimum in the net CO₂ uptake rate. A smaller, but O₂-insensitive post-illumination burst was observed following a 30-min illumination period, when net CO₂ uptake was at a steady-state rate. These post-illumination bursts appeared to reflect the release of an intracellular pool of inorganic carbon, which was much larger following the initial surge of net CO₂ uptake than during the subsequent steady-state CO₂ uptake period.With the mutant in CO₂-free gas, O₂-stimulated, net CO₂ efflux was observed in the light, and a small, O₂-dependent post-illumination burst was observed. With wild-type cells no CO₂ efflux was observed in the light in CO₂-free gas under either 2% or 21% O₂, but a small, O₂-dependent post-illumination burst was observed. These results were interpreted as indicating that photorespiratory rates were similar in the mutant and wild-type cells in the absence of CO₂, but that the wild-type cells were better able to scavenge the photorespiratory CO₂.     

Biochemistry of C3-photosynthesis in high CO2

The short-term responses of C₃ photosynthesis to high CO₂ are described first. Regulation of photosynthesis in the short term is determined by interaction among the capacities of light harvesting, electron transport, ribulose-1, 5-bisphosphate carboxylase (Rubisco) and orthophosphate (Pi) regeneration during starch and sucrose synthesis. Photosynthesis under high CO₂ conditions is limited by either electron transport or Pi regeneration capacities, and Rubisco is deactivated to maintain a balance between each step in the photosynthetic pathway. Subsequently, the long-term effects on, photosynthesis are discussed. Long-term CO₂ enhancement leads to carbohydrate accumulation. Accumulation of carbohydrates is not associated with a Pi-regeneration limitation on photosynthesis, and this limitation is apparently removed during long-term exposure to high CO₂. Enhanced CO₂ does not affect Rubisco content and electron transport capacity for a given leaf-nitrogen content. In addition, the deactivated Rubisco immediately after exposure to high CO₂ does not recover during the subsequent prolonged exposure. Such evidence may indicate that plants do not necessarily have an ideal acclimation response to high CO₂ at the biochemical level.     

Effects of elevated CO2 and O3 on N-cycling and N2O emissions: a short-term laboratory assessment

Background and aims

Elevated atmospheric CO₂ (eCO₂) and tropospheric O₃ (eO₃) can alter soil microbial processes, including those underlying N₂O emissions, as an indirect result of changes in plant inputs. In this study, effects of eCO₂ and eO₃ on sources of N₂O in a soybean (Glycine max (L.) Merr.) agroecosystem in Illinois (SoyFACE) were investigated. We hypothesized that increases in available C and anaerobic microhabitat under eCO₂ would stimulate N₂O emissions, with a proportionally larger increase in denitrification derived N₂O (N₂O_D) compared to nitrification plus nitrifier denitrification derived N₂O (N₂O_N+ND). We expected opposite effects under eO₃.

Methods

Isotopically labeled ¹⁵NH ₄ ¹⁴ NO₃ and ¹⁴NH ₄ ¹⁵ NO₃ were used to evaluate mineral N transformations, N₂O_D, and N₂O_N+ND in a 12-day incubation experiment.

Results

We observed minimal effects of eCO₂ and eO₃ on N₂O emissions, movement of ¹⁵?N through mineral N pools, soil moisture content and C availability. Possibly, altered C and N inputs by eCO₂ and eO₃ were small relative to the high soil organic C content and N-inputs via biological N₂-fixation, minimizing potential effects of eCO₂ and eO₃ on N-cycling.

Conclusion

We conclude that eCO₂ and eO₃ did not affect N₂O emissions in the short term. However, it remains to be tested whether N₂O emissions in SoyFACE will be unaltered by eCO₂ and eO₃ on a larger temporal scale under field conditions.     

Aspen-associated mycorrhizal fungal production and respiration as a function of changing CO2, O3 and climatic variables

The relationships of mycorrhizal fungal respiration and productivity to climate and atmospheric chemistry remain under characterized. We quantified mycorrhizal sporocarp and hyphal respiration, as well as growing season net hyphal production, under ambient and elevated carbon dioxide (CO₂) and ozone (O₃) in relation to natural temperature and moisture variation. Hyphal respiration did not respond significantly to elevated CO₂ and O₃. Sporocarp respiration was affected by temperature and moisture content while hyphal respiratory response to temperature was undetected over the narrower range of soil temperatures captured. Hyphal respiration comprised 31 % of soil respiration, and the ratio of hyphal respiration to soil respiration declined with elevated CO₂. Hyphal biomass was reduced under all treatments though not statistically significant. Given the large fraction of soil respiration represented by mycorrhizal fungi and its sensitivity to climate, a small change in fungal respiration could strongly affect carbon budgets and cycling under climate change.     

Effect of O2:CO2 ratio on the primary metabolism of Chlamydomonas reinhardtii

High oxygen:carbon dioxide ratios may have a negative effect on growth and productivity of microalgae. To investigate the effect of O₂ and CO₂ concentrations and the ratio between these on the metabolism of Chlamydomonas reinhardtii we performed turbidostat experiments at different O₂:CO₂ ratios. These experiments showed that elevated O₂ concentrations and the corresponding increase in the ratio of O₂:CO₂ common in photobioreactors led to a reduction of growth and biomass yield on light with 20–30%. This is most probably related to the oxygenase activity of Rubisco and the resulting process of photorespiration. Using metabolic flux modeling with measured rates for each experiment we were able to quantify the ratio of the oxygenase reaction to the carboxylase reaction of Rubisco and could demonstrate that photorespiration indeed can cause the reduction in biomass yield on light. The calculated ratio of the oxygenase reaction to the carboxylase reaction was 16.6% and 20.5% for air with 2% CO₂ and 1% CO₂, respectively. Thus photorespiration has a significant impact on the biomass yield on light already at conditions common in photobioreactors (air with 2% CO₂). Biotechnol. Bioeng. 2011;108: 2390–2402. © 2011 Wiley Periodicals, Inc.     

Elevated CO2 reduces O3 flux and O3-induced yield losses in soybeans: possible implications for elevated CO2 studies

Soybeans were grown for three seasons in open-top field chambersto determine (1) whether elevated CO₂ (360 versus 700 µmolmol^–1) alleviates some of the yield loss due to pollutantO₃, (2) whether the partial stomatal closure resulting fromchronic O₃ exposure (charcoal-filtered air versus 1.5 ambientconcentrations) is a cause or result of decreased photosynthesis,and (3) possible implications of CO₂/O₃ interactions to climatechange studies using elevated CO₂. Leaf conductance was reducedby elevated CO₂, regardless of O₃ level, or by exposure to O₃alone. As.a result of these effects on conductance, high CO₂reduced estimated midday O₃ flux into the leaf by an averageof 50% in charcoal-filtered air and 35% in the high O₃ treatment.However, while exposure to O₃ reduced seed yields by 41% atambient CO₂ levels, the yield reduction was completely amelioratedby elevated CO₂. The threshold midday O₃ flux for yield lossappears to be 20–30 nmol m^–2 s^–1 in this study.Although elevated CO₂ increased total biomass production, itdid not increase seed yields. A/C_i curves show a large reductionin the stomatal limitation to photosynthesis due to elevatedCO₂ but no effect of O₃. These data demonstrate that (1) reducedconductance due to O₃ is the result, and not the cause, of reducedphotosynthesis, (2) 700 µmol mol^–1 CO₂ can completelyameliorate yield losses due to O₃ within the limits of theseexperiments, and (3) some reports of increased yields underelevated CO₂ treatments may, at least in part, reflect the ameliorationof unrecognized suppression of yield by O₃ or other stresses. Key words: Stomatal limitation, elevated CO₂, O₃ flux, Glycine max, yield suppression