Calibration of Infra-red CO(2) Gas Analyzers

Precision gas mixing pumps produce CO₂ gas mixtures for the calibration of infra-red CO₂ gas analyzers equivalent in accuracy to the standard CO₂ gas mixtures (± 1%) supplied by the National Bureau of Standards, Washington, D. C.     

Development of a system for the on‐line measurement of carbon dioxide production in microbioreactors: Application to aerobic batch cultivations of Candida utilis

We developed and applied a conductometric method for the quantitative online measurement of the carbon dioxide (CO₂) production during batch cultivations of Candida utilis on a 100‐μL scale. The applied method for the CO₂ measurement consisted of absorption of the produced CO₂ from the exhaust gas of the microbioreactor in an alkali solution, of which the conductivity was measured on‐line. The measured conductivity change of the alkali solution showed a linear relation with the total amount of CO₂ absorbed. After calibration of the CO₂ measurement system, it was connected to a well of a 96‐well microtiter plate. The mixing in the well was achieved by a magnetic stirrer. Using online measurement of the CO₂ production during the cultivation, we show reproducible exponential batch growth of C. utilis on a 100‐μL scale. The CO₂ production measurements obtained from the microcultivation were compared with the CO₂ production measurement in a 4‐L bioreactor equipped with a conventional off‐gas analyzer. The measurements showed that on‐line measurement of the CO₂ production rate in microbioreactors can provide essential data for quantitative physiological studies and provide better understanding of microscale cultivations. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

A new method for measuring 13carbon abundance in tracer experiments

Abstract. A new technique for the precise measurement of ¹³C-abundance and concentration is described. It is based on the differences in infra-red spectra between ¹²CO₂ and ¹³CO₂ and can be applied to gas mixtures or organic materials which have been oxidized to CO₂. The gas mixture is first dried and then passed through two infra-red gas analysers (IRGAs) connected in parallel. The two IRGAs are fitted with different optical filters so they differ in their relative sensitivities to ¹²CO₂ and ¹³CO₂. Once these sensitivities are known then simple algebra allows the concentrations of ¹²CO₂ and ¹³CO₂ to be calculated from the two readings. Two variants of this basic system have been tested. In both, one IRGA was a normal commercial instrument with a narrow band pass interference filter making it highly specific for ¹²CO₂; the second instrument was fitted with either a wide-band pass filter covering both the ¹²CO₂ and ¹³CO₂ absorption bands, or a narrow band pass filter specific for ¹³CO₂. These variations convey different advantages in operation. The wide-band system can be easily calibrated using a single natural abundance ¹²CO₂ standard but is only moderately precise at low abundances. It is particularly valuable for continuous monitoring of the relatively high abundance sources used in plant photosynthesis experiments. The narrow-band system gives high precision but requires a more complex standardization procedure. It is recommended for measurements on low-abundance samples resulting from tracer experiments. Here, its high sensitivity permits measurements on samples as small as 3 μmole C, thus enabling plant fractions and individual metabolites to be investigated. While the wide-band system can be manually operated under field conditions, it is necessary for highest precision to use computerized data collection and linearization. These processes are described, as are novel techniques for standardization, the preparation of small quantities of CO₂ of known abundance, and the transfer of gas samples from oxidizer to analyser. Determinations by the wide band system of % abundance in standard gas mixtures gave a standard error of ±0.03% but this increased to over ±0.1% for abundances below 20%. Corresponding values for the narrow-band system were ±0.01% over the whole abundance range an accuracy almost identical to that observed with an organic mass spectrometer. Two pulse-chase experiment with ¹³CO₂ are described in which the technique was used for studies on growth and metabolism of Lemna minor. The first demonstrated that ¹³C-accumulation within the plants matched closely the predictions from the net assimilation rate and measurements of ¹³C-abundance in the gas phase. The second revealed the rapid changes in the ¹³C-labelling of some plant components during pulse and chase phases. These examples demonstrate the potential of the method for studies in plant physiology and biochemistry. In view of its relative cheapness, ease of maintenance and operation, accuracy, and sensitivity, it is suggested that this new method may encourage a wider use of the safe stable ¹³C for biological and medical applications.     

Soil properties differently influence estimates of soil CO2 efflux from three chamber-based measurement systems

Soil CO₂ efflux is a major component of net ecosystem productivity (NEP) of forest systems. Combining data from multiple researchers for larger-scale modeling and assessment will only be valid if their methodologies provide directly comparable results. We conducted a series of laboratory and field tests to assess the presence and magnitude of soil CO₂ efflux measurement system × environment interactions. Laboratory comparisons were made with a dynamic, steady-state CO₂ flux generation apparatus, wherein gas diffusion drove flux without creating pressure differentials through three artificial soil media of varying air-filled porosity. Under these conditions, two closed systems (Li-6400-09 and SRC-1) exhibited errors that were dependent on physical properties of the artificial media. The open system (ACES) underestimated CO₂ flux. However, unlike the two other systems, the ACES results could be corrected with a single calibration equation that was unaffected by physical differences in artificial media. Both scale and rank changes occurred among the measurement systems across four sites. Our work clearly shows that soil CO₂ efflux measurement system × environment interactions do occur and can substantially impact estimates of soil CO₂ efflux. Until reliable calibration techniques are developed and applied, such interactions make direct comparison of published rates, and C budgets estimated using such rates, difficult.     

Measurement of breath-by-breath gas exchange during general anaesthesia using a single pneumotachograph

A breath-by-breath gas exchange measurement system using a single pneumotachograph suitable for use during general anaesthesia is described. The system's accuracy has been assessed by a combination of error sensitivity analysis, laboratory testing of the component measurements used to calculate gas exchange and measurements on volunteers and patients. The system is shown to have a mean accuracy of ± 2.6 ml breath⁻¹ for V_CO2 measurements, ± 7.12 ml breath⁻¹ for V_O2 and ± 5.55 ml breath⁻¹ for V_N2O measurement. The application of a lung gas stores correction using argon improved between breath variability by 50%.     

Effect of CO2 on succinate production in dual-phase Escherichia coli fermentations

Succinate production under different concentrations of carbon dioxide (CO₂) was studied in Escherichia coli AFP111, which contains mutations in pyruvate formate lyase (pfl), lactate dehydrogenase (ldhA) and the phosphotransferase system glucosephosphotransferase enzyme II (ptsG). A series of two-phase fermentations were conducted in which an aerobic cell growth phase was followed by an anaerobic succinate production phase using several constant concentrations of CO₂. As the concentration of CO₂ in the gas phase increased from 0% to 50%, the succinate specific productivity increased from 1.9 mg/g h to 225 mg/g h, and the succinate yield increased from 0.04 g/g to 0.75 g/g. Above 50% CO₂, succinate production did not increase further. Intracellular fluxes were determined at three different CO₂ concentrations (3%, 10%, and 50%) using ¹³C-label tracing coupled with LC–MS analysis. The fraction of carbon flux into the pentose phosphate pathway increased from 0.04 at 3% CO₂ to 0.17 at 50% CO₂. Also, the fractional flux through anaplerotic carboxylation at the phosphoenolpyruvate (PEP) node increased slightly from 0.53 at 3% CO₂ to 0.63 at 50% CO₂. The increased flux into the pentose phosphate pathway is attributed to an increased demand for reduced cofactors with elevated CO₂. A four-process explicit model to describe the CO₂ transfer and utilization was proposed. The model predicted that at CO₂ concentrations below about 30–40% the system becomes limited by gas phase CO₂, while at higher CO₂ concentrations the system is limited by PEP carboxylase enzyme kinetics.     

A field portable gas-exchange system for measuring carbon dioxide and water vapour exchange rates of leaves during fumigation with SO2

Abstract A field portable, steady-state gas-exchange system which measures both CO₂ and water vapour exchange of single intact leaves during fumigations with SO₂ is described. Within the leaf cuvette temperature, light, humidity and both CO₂ and SO₂ concentrations are controlled to preset levels. Gas flow and concentrations are controlled by mass flow controllers. Photosynthetic uptake of CO₂ can be determined either by differential depletion or null balance measurement. Water vapour exchange is measured differentially and transpiration and conductance to water vapour determined. Sulphur dioxide is measured directly within the cuvette exhaust gas line by UV-pulse fluorescence. The performance of this system under field conditions is described and the physiological measurements compared with those obtained with other systems.     

A sensitive technique for the rapid measurement of carbon dioxide concentrations

A method has been developed to measure concentrations of CO₂ in gases rapidly. A gas sample is injected into a flowing carrier gas that passes through an infrared CO₂ analyzer. A strip chart recorded peak response is obtained which is proportional to the CO₂ concentration. A resolution of better than 2 microliters of CO₂ per liter of gas was obtained. Seven to 10 seconds were required for sample analysis once the sample was obtained. Sorghum bicolor plant respiration was determined at different temperatures by measuring CO₂ using this system and by using a conventional system. The correlation between techniques was 0.996, and about the same variation occurred within each method. This technique greatly increased the efficiency of the infrared CO₂ analyzer in our laboratory for use in plant respiration and photosynthetic studies.     

A gas phase chromatography method for determination of low dissolved CO2 concentration and/or CO2 solubility in microbial culture media

CO₂ concentration in aqueous samples was derived from determination of the CO₂ content in the gas phase at equilibrium with the liquid by gas chromatography. This technique was used to measure low dissolved CO₂ concentrations, down to 10^–6 mol/L, and CO₂ solubility in microbial culture media. The method gave results with an accuracy within 10%, and appeared thus as reliable and sensitive. It could be considered as a valuable tool to study CO₂ mass transfer in bio-processes.     

Evaluation of photoacoustic infrared spectroscopy for simultaneous measurement of N2O and CO2 gas concentrations and fluxes at the soil surface

Simultaneous measurement of N₂O and CO₂ flux at the soil surface with photoacoustic infrared spectroscopy (PAS) is gaining popularity due to portability, low maintenance, and ease‐of‐operation. However, the ability of PAS to measure N₂O with accuracy and precision similar to gas chromatography (GC) is uncertain due to overlap in N₂O, CO₂, and H₂O absorbance spectra combined with the large range in analyte concentrations. We tested the ability of six PAS units to simultaneously measure N₂O and CO₂ gas concentrations and fluxes with accuracy and precision similar to two GC units. We also evaluated H₂O vapor and CO₂ interferences with N₂O measurement. The accuracy and precision of standard gas concentration measurements with PAS and GC were similar. High water vapor (~26 600 ppm) and CO₂ concentrations (~4500 ppm) did not interfere with N₂O measurement across the concentration range typically observed in static flux chambers at the soil surface (~0.5–3.0 ppm N₂O). On average, N₂O fluxes measured with the six PAS were 4.7% higher than one GC and 9.9% lower than the second GC.     

On-line measurements of C enrichments in rat breath: Non-invasive method for in vivo study of drug enzymatic induction

A differential kinetic study of ¹³CO₂ enrichment of breath after the intake of specific ¹³C-labelled substrates and co-administration of a drug allows the drug's ability for enzyme induction to be evaluated in vivo. A method and a gas chromatograph—isotope ratio mass spectrometer device for on-line measurements of ¹³CO₂ enrichment in the breath of small animals are described. This system allows on-line breath sample collection from a metabolic cage, purification by gas chromatography, determination of CO₂ by thermal conductivity detection and measurement of ¹³CO₂ enrichment by isotope ratio mass spectrometry. Two protocols for phenobarbital-inducible P450 and 3-methylcholanthrene-inducible P1-450 isoenzymes are described.     

The concentration and efflux of tree stem CO2 and the role of xylem sap flow

The accurate assessment of actual tree stem respiration and its relation with temperature plays a considerable role in investigating the forest carbon cycle. An increasing number of research reports have indicated that tree stem respiration determined with the commonlyapplied chamber gas exchange measuring system does not follow expectations regarding temperature relationships. This method is based on the nowadays widely-accepted theory that the respired CO₂ in a tree stem would all diffuse outward into the atmosphere. However, it neglects partial CO₂ that is dissolved in the xylem sap and is carried away by the transpirational stream. Scientists have started to realize that the respired CO₂ measured with the chamber gas exchange method is only a portion of the total stem respiration (CO₂ efflux), while the other portion, which is sometimes very substantial in quantity (thought to occupy maybe 15%–75% of the total stem respiration), is transported to the upper part of the stem and to the canopy by sap flow. This suggests that the CO₂ produced by respiration is re-allocated within the stem. Accordingly, the change in CO₂ efflux could be reflected in the rates of sap flow in addition to its dependence on temperature. Proper methods and instruments are required to quantify the internal and external CO₂ fluxes in the trunk and their interaction with related environmental factors.     

Carbon dioxide capture using covalent organic frameworks (COFs) type material—a theoretical investigation

The present work deals with a density functional theory (DFT) study of porous organic framework materials containing – groups for CO₂ capture. In this study, first principle calculations were performed for CO₂ adsorption using N-containing covalent organic framework (COFs) models. Ab initio and DFT-based methods were used to characterize the N-containing porous model system based on their interaction energies upon complexing with CO₂ and nitrogen gas. Binding energies (BEs) of CO₂ and N₂ molecules with the polymer framework were calculated with DFT methods. Hybrid B3LYP and second order MP2 methods combined with of Pople 6-31G(d,p) and correlation consistent basis sets cc-pVDZ, cc-pVTZ and aug-ccVDZ were used to calculate BEs. The effect of linker groups in the designed covalent organic framework model system on the CO₂ and N₂ interactions was studied using quantum calculations.     

Impacts of climate change on paddy rice yield in a temperate climate

The crop simulation model is a suitable tool for evaluating the potential impacts of climate change on crop production and on the environment. This study investigates the effects of climate change on paddy rice production in the temperate climate regions under the East Asian monsoon system using the CERES‐Rice 4.0 crop simulation model. This model was first calibrated and validated for crop production under elevated CO₂ and various temperature conditions. Data were obtained from experiments performed using a temperature gradient field chamber (TGFC) with a CO₂ enrichment system installed at Chonnam National University in Gwangju, Korea in 2009 and 2010. Based on the empirical calibration and validation, the model was applied to deliver a simulated forecast of paddy rice production for the region, as well as for the other Japonica rice growing regions in East Asia, projecting for years 2050 and 2100. In these climate change projection simulations in Gwangju, Korea, the yield increases (+12.6 and + 22.0%) due to CO₂ elevation were adjusted according to temperature increases showing variation dependent upon the cultivars, which resulted in significant yield decreases (?22.1% and ?35.0%). The projected yields were determined to increase as latitude increases due to reduced temperature effects, showing the highest increase for any of the study locations (+24%) in Harbin, China. It appears that the potential negative impact on crop production may be mediated by appropriate cultivar selection and cultivation changes such as alteration of the planting date. Results reported in this study using the CERES‐Rice 4.0 model demonstrate the promising potential for its further application in simulating the impacts of climate change on rice production from a local to a regional scale under the monsoon climate system.     

Enhancement of CO2 tolerance of Chlorella vulgaris by gradual increase of CO2 concentration

Summary Chlorella vulgaris UTEX259 was cultivated using two different methods of gas supply. In one method the CO₂ concentration in bubbled gas was held constant and in the other method it was increased gradually. Algal growth was almost linear after a short period of lag phase in both methods. With the constant CO₂ concentration, the CO₂ fixation rate in the linear growth phase decreased over 10%(v/v) CO₂, while the rate increased up to 6% CO₂. However, the rate was enhanced by using the latter incremental increase method, especially under a higher concentration of CO₂. The maximum rate of CO₂ fixation was 52 mg CO₂/l·h at 20% CO₂ during the gradual increase of CO₂ concentration.     

A method for measuring whole plant photosynthesis in Arabidopsis thaliana

Measurement of photosynthesis of intact leaves of Arabidopsis thaliana has been prohibitive due to the small leaf size and prostrate growth habit. Because of the widespread use of Arabidopsis for plant science research it is important to have a procedure for accurate, nondestructive measurement of its photosynthesis. We developed and tested a method for analysis of photosynthesis in whole plants of Arabidopsis. Net carbon assimilation and stomatal conductance were measured with an open gas exchange system and photosynthetic oxygen evolution was determined from chlorophyll fluorescence parameters. Individual plants were grown in 50 cubic centimeter tubes that were attached with an air tight seal to an enclosed gas exchange chamber for measurement of carbon dioxide and water exchange by the whole plant. Chlorophyll fluorescence from intact leaves was simultaneously measured with a pulse modulated fluorometer. Photosynthetic CO₂ assimilation and stomatal conductance rates were calculated with established gas exchange procedures and O₂ evolution was determined from chlorophyll fluorescence measurement of Photosystem II yield. Carbon assimilation and oxygen evolution in response to light intensity and ambient CO₂ concentration was measured and is presented here to demonstrate the potential use of this method for investigation of photosynthesis of Arabidopsis plants in controlled environment conditions.     

Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplar

It is a matter of debate if there is a direct (short‐term) effect of elevated atmospheric CO₂ concentration (C_a) on plant respiration in the dark. When C_a doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15–20%. The present study shows that the measurement artefacts – particularly leaks between leaf chamber gaskets and leaf surface, CO₂ memory and leakage effects of gas exchange systems as well as the water vapour (‘water dilution’) effect on DCO₂ measurement caused by transpiration – may result in larger errors than generally discussed. A gas exchange system that was used in three different ways – as a closed system in which C_a increased continuously from 200 to 4200 mmol (CO₂) mol^‐1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during C_a periods of either 350 or 2000 mmol mol^‐1, and as an open system in which C_a varied between 350 and 2000 mmol mol^‐1– is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short‐term changes in CO₂ on dark CO₂ efflux of bean and poplar leaves were found, even when C_a increased to 4200 mmol mol^‐1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO₂.     

Soil respiration response to three years of elevated CO2 and N fertilization in ponderosa pine (Pinus ponderosa Doug. ex Laws.)

We measured growing season soil CO₂ evolution under elevated atmospheric [CO₂] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO₂] treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO₂ (ambient, + 175, and +350 L L^–1 CO₂) and N (0, 10, and 20 g m^–2 N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO₂ evolution was measured over diurnal periods (20–22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow-through, infrared gas analyzer measurement system and corresponding pCO₂ measurements were made with gas wells. Significantly higher soil CO₂ evolution was observed in the elevated CO₂ treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO₂, and +350 CO₂ respectively).Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO₂ evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18°C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001; n = 56) with the pCO₂ measurement method.     

Whole Plant CO(2) Exchange Measurements for Nondestructive Estimation of Growth

A computer controlled semiclosed net CO₂ exchange measurement system, employing an infrared gas analyzer and mass flow controllers to inject pure CO₂ at preset rates, has been developed for measuring whole plant net CO₂ exchange and net C gain in a controlled environment (i.e. CO₂, light, and temperature). Data for tomato (Lycoperscicon esculentum cv Campbell 19 VF) and rose (Rosa hybrida cv Samantha) plants grown for 4 and 17 day periods, respectively, clearly show that net C gain measured and computed using nondestructive CO₂ analysis equaled the increase in C content determined by chemical analysis following destruction of the test plants. The analysis of C gain based on CO₂ exchange allows estimation of biomass production and growth of a single population of plants under varying light and CO₂ conditions without physically handling the test plants.