CO2 Uptake Efficiency Research Articles

Synthesis of [3 + 3] β-ketoenamine-tethered covalent organic frameworks (COFs) for high-performance supercapacitance and CO2 storage

Abstract We report three new β-ketoenamine-linked covalent organic frameworks (COFs) prepared through Schiff-base [3 + 3] polycondensations of 1,3,5-triformylphloroglucinol (TFP-3OHCHO) with three tris(aminophenyl)-presenting derivatives—featuring amino, carbazole, and pyridine units, respectively under solvothermal conditions. The resultant TFP-COFs possessed high BET specific surface area up to 686 m2 g–1 and excellent crystallinity, which showed excellent electrochemical specific capacitances (up to 291.1 F g–1) and CO2 uptake efficiency up to 200 mg g–1 at 273 K. We propose the enhanced performance in supercapacitor and gas storage is owing to the conjugated enamine structures with redox-active triphenyl amino, carbazole, and pyridine moieties. In addition, we further investigate the formation mechanism of the spherical TFP-TPA COF by studying the morphological changes over time. The presence of more highly planar monomer units in the hexagonal structures of the resultant COFs led to stronger quadrupolar interaction with the included CO2 molecules.

The ideal percentage of K substitution by Na in Eucalyptus seedlings: Evidences from leaf carbon isotopic composition, leaf gas exchanges and plant growth

Potassium (K) is the most required macronutrient by Eucalyptus, while sodium (Na) can partially substitute some physiological functions of K and have a positive response on plant growth in K-depleted tropical soils. However, the right percentage of K substitution by Na is not yet known for Eucalyptus seedlings, since a few experiments have only compared treatments receiving K or Na. This study evaluated five levels of Na supply (0, 0.45, 0.90, 1.35 and 1.80 mM) as substitution for K in Eucalyptus seedlings grown in nutrient solution. Plants growth, biomass, K-nutritional status, leaf gas exchange, leaf carbon isotopic composition (δ13C ‰), leaf water potential (Ψw), leaf area (LA), stomatal density (SD) and water use efficiency (WUE) were measured. The highest total biomass yield was achieved by the Na estimated rate of 0.25 mM, corresponding to a leaf K: Na ratio of 3.41, and having the lowest δ13C values. Conversely, the highest Na rate (1.8 mM) induced K deficiency symptoms, lower growth, reduced total dry matter yield, leaf gas exchange, LA, SD and a higher δ13C, which presented a trend to an inverse correlation with CO2 assimilation rate (A), WUE and shoot dry matter. Collectively, our results conclude that substitution of 25% of K by Na (0.45 mM of Na) provided significant gains in nutritional status and positive plant physiological responses by increasing WUE, stomatal diffusion, and by augmenting CO2 uptake efficiency. This nutritional management can therefore be an alternative option to optimize yields and resource use efficiencies in Eucalyptus cultivation.

Potential of a liquid foam-bed photobioreactor for microalgae cultivation

The liquid foam-bed photobioreactor is a novel photobioreactor for microalgae cultivation. A mathematical model was developed to evaluate its potential, and to optimize the design and operation of a large-scale unit. This model describes light limited microalgal growth in a rising foam column in a foam-bed photobioreactor, which is continuously operated at constant biomass density. The microalgae-containing liquid is recirculated from the bottom of the reactor and dispersed equally on the top of the foam column, in order to ensure homogenous microalgae distribution and a wet and stable foam. The model combines calculations of liquid fraction gradient, light penetration, microalgal growth, and gas transfer in the foam-bed. The liquid fraction and light model was experimentally validated. The areal productivity of a 5 cm deep foam-bed photobioreactor operated at 30 g L−1 microalgae and 1500 μmol photons m−2 s−1 was estimated to be 67.7 g m−2 d−1. This productivity is slightly lower compared to what is achievable in flat panels, which is related to light scattering in the foam-bed. Nevertheless, the advantages of the foam-bed photobioreactor, such as high gas transfer rate and high biomass densities, were confirmed with the simulations. In addition, it was calculated that a CO2 uptake efficiency of 97% can be obtained ensuring minimal CO2 loss. These benefits result in reduced gas supply requirement and reduced energy required for downstream processing. The total energy required for the production and separation of 1 g biomass in liquid foam-beds is only 8.5% of what is required in flat panels with suspended biomass. These results highlight the potential of foam-bed photobioreactors for large scale application for microalgae production.

Reversible carbon dioxide capture by aqueous and non-aqueous amine-based absorbents: A comparative analysis carried out by 13C NMR spectroscopy

The efficiency of CO2 uptake by the amines 2-(2-aminoethoxy)ethanol (DGA), 2-amino-2-methyl-1,3-propanediol (AMPD), 2-amino-2-methyl-1-propanol (AMP), 2,2′-iminodiethanol (DEA) and 2-(butylamino)ethanol (BUMEA) has been investigated either in aqueous and in 2-(2-methoxyethoxy)ethanol (DEGMME) solutions and compared with 30% aqueous 2-aminoethanol (MEA). Batch experiments were carried out to measure the CO2 loading capacity of the different amine solutions and the rate of CO2 absorption. The 13C analysis has been applied to identify and quantify the carbonated species in solution upon CO2 uptake. The efficiency of CO2 (15% in air) capture was measured in continuous cycles of absorption (40 °C) and desorption (110 °C) carried out in packed columns at room pressure. The efficiency of the aqueous absorbents is greater than 90% and overcomes that in 2-(2-methoxyethoxy)ethanol. The CO2 absorption heat of aqueous BUMEA and DGA in DEGMME calculated using Gibbs–Helmholtz equation was found to be lower than that of conventional 30% aqueous MEA: the possible advantages of these systems with respect to aqueous MEA as CO2 absorbents have been discussed.

Increasing microalgal lipid productivity for conversion into biodiesel by using a non-energy consuming light guide

Mass cultivation of photosynthetic microalgae combined with mitigation of carbon dioxide (CO2) emissions from industrial off-gases to produce lipids as a biodiesel feedstock can help environmental sustainability. However, traditional open microalgae mass cultivation systems that use sunlight are typically no more than 30 cm deep due to light attenuation and self-shading by the mircroalgae and, therefore, have low CO2 uptake efficiency due to their shallow depth. To address this issue, a non-energy consuming light guide was employed to diffuse light deep into a top-lit, 120 cm deep open gas-lift cultivation system. This gas-lift system has been already shown to increase areal biomass productivity by 60%. Without any increase in supplied light energy, the light guide enhanced light penetration into the bioreactor and resulted in further increases in biomass and lipid productivities per unit area of 33% and 16%, respectively. The factors influencing light and CO2 absorption rates were investigated with a Plackett-Burman experimental design. Mathematical models for predicting biomass and lipid production as well as optimal bioreactor configurations for maximizing lipid production and minimizing production costs were then determined by applying response surface methodology. The optimum configuration of operational parameters identified by the optimization function was then verified in the gas-lift bioreactor equipped with the light guide and resulted in areal biomass productivity of 34.4 gdw/m2day and areal lipid production of 223.9 gLipid/m2.

Influence of the functionalization of imidazole on its CO2 uptake efficiency. A theoretical contribution

New capture and sequestration technologies have been proposed to mitigate CO2 emissions motivating the search for new materials such as MOF’s, ZIF’s and other porous solids. In this paper, the influence of the substitution of imidazole by different donor and acceptor groups on the CO2 uptake efficiency is analyzed. Imidazoles are important organic units of the ZIF’s.Geometries and energies of the different complexes have been optimized using the Density Functional (DFT) and Möller–Plesset (MP2) theories with cc-pVTZ and aug-cc-pVTZ atomic orbitals basis sets. For DFT calculations, the WB97XD functional, suitable for the description of dispersion forces and Van der Waals interactions, has been used. The preferred configurations of the substituted imidazoles are planar, favoring the CO2 approach to the sp2 type nitrogen. Binding energies are determined minimizing the basis set superposition error and taking into account the zero point energies. The interaction between imidazole and different greenhouse effect gases such as H2O, N2, CH4, NH3 and SO2 are also studied in order to demonstrate the selectivity of imidazole for CO2 capture. The imidazole molecules (or the ZIF’s) can then be used for selective separation of CO2 in gas mixture containing CO2, N2, and CH4 of industrial flues. However, it can be noticed that imidazoles are not adequate for gas mixture containing H2O and CO2 or NH3 and CO2. The behavior of imidazolates in dry or humid environments is predicted to be very different. The effect of the substitution of the imidazole hydrogens by one, two, or three active groups on the CO2 capture and storage is also analyzed. The selected groups are OH, CN, CH3, NH2, COH, Cl, CF3, OCH3 and C(CH3)3.

Enhanced gas sorption properties of a new sulfone functionalized aluminum metal-organic framework: Synthesis, characterization, and DFT studies

A new sulfone-functionalized analogue of DUT-5 ([Al(OH) (BPDC)], BPDC = 4,4′-biphenyldicarboxylate) microporous metal-organic framework, [Al(OH) (SBPDC)] (1) (H2SBPDC = 2,2′-sulfone-4,4′-biphenyldicarboxylate), has been synthesized in order to achieve better gas sorption properties over DUT-5. The compound was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, variable temperature PXRD, thermogravimetric analysis, FT-IR spectroscopy, NMR spectroscopy and gas adsorption measurements. The new MOF forms a 3D porous framework containing 1D inorganic chains which are formed by corner-sharing octahedral AlO6 connected through SBPDC linkers. As determined by gas sorption measurements, the compound 1 exhibits high porosity with the H2 uptake capacity of 8.58 mmol g−1 at 77 K (1 atm) and CO2 uptake of 2.51 mmol g−1 at 298 K (1 atm) or 4.40 mmol g−1 at 273 K (1 atm). The gas sorption experimental results suggested that compound 1 with sulfone functionalized ligand showed higher CO2 and H2 gas uptake than that of isoreticular MOF, DUT-5. The CO2 gas sorption behavior of 1 and DUT-5 has been analyzed with the aid of DFT studies which explained that the sulfone group can enhance the efficiency of CO2 uptake.

Decadal (1994–2008) change in the carbon isotope ratio in the eastern South Pacific Ocean

AbstractWe determined the 14 year change in the anthropogenic CO2 inventory in the eastern South Pacific Ocean along the 110°W meridian from 67°S to 21°N, using seawater δ13C data sets collected in 1994 and 2008. The vertical integral of the 14 year δ13C change was assessed in five latitude bands and found to be greatest (−14.7‰ m yr−1) in the subpolar band (38°S–55°S) and smallest (−3.0‰ m yr−1) in the tropical band (21°N–18°S). The δ13C change in each of the latitudinal bands was primarily caused by inputs of anthropogenic CO2 via air‐sea exchange and transport. More than 50% of the total anthropogenic CO2 was added to the subpolar band via the northward movement of Antarctic Intermediate Water (AAIW) from the south, and the remaining 50% was added via air‐sea exchange. We also calculated the ratio of the temporal change in δ13C to the change in dissolved inorganic carbon, which is a measure of the efficiency of oceanic uptake of anthropogenic CO2. The ratio for AAIW in 1994 (−0.017‰ (µmol kg−1) −1) was greater than that in 2008 (−0.010‰ (µmol kg−1) −1) based on the change in preformed δ13C and dissolved inorganic carbon (DIC), indicating reduced efficiency of CO2 uptake by the Southern Ocean in 2008 relative to that in 1994. AAIW remained at the surface for a shorter period in 2008 relative to 1994, and thus would have taken up less atmospheric CO2 prior to subduction. The projected reduction in this ratio indicates a weakening of CO2 uptake by the Southern Ocean in the future.

CO2 Capture by CaO in Molten CaF2–CaCl2: Optimization of the Process and Cyclability of CO2 Capture

CO2 capture by CaO dissolved or partly dissolved in a molten salt shows high, reversible CO2 sorption because of rapid gas–liquid interactions. Using previously obtained data on CaO reactivity with CO2 in a CaCl2 melt, we describe here the application of the CaF2–CaCl2 molten salt for CaO dissolution or partly dissolution in a CO2 capture process. The effects of the CaO concentration in CaF2–CaCl2 (ratio fixed to the eutectic composition), temperature, and gas composition (CO2–N2) on the carbonation/decarbonation reactions in a one-chamber atmospheric pressure reactor were established by means of a Fourier transform infrared (FTIR) gas detector and gravimetric analysis. The CO2 uptake efficiency by CaO dissolved or partly dissolved in the metal halides was found to enhance and stabilize with concentrations of CaO exceeding 10 wt % in CaF2–CaCl2 in the temperature range of 670–710 °C. Desorption of CO2, performed by a thermal swing technique, proceeded rapidly and completely at 927–946 °C. The CaO activity...

Mineral carbonation by blowing incineration gas containing CO2 into the solution of fly ash and ammonia for ex situ carbon capture and storage

The feasibility study on the accelerated mineral carbonation reveals that the addition of ammonia was important in the simplified two-step carbonation reaction, and that micro-bubbling and gas inflow speed were main factors for the reactions. The efficiency of CO2 uptake was 33.9% in the first step of carbonation process and increased to 58.6% in the second step. Calcium carbonate was obtained as product of Ca conversion up to 56.6% as a maximum conversion, through first and second carbonations. In the mineralogical analysis of ash, XRD pattern showed that, as carbonation proceed, the peaks of Ca(OH)2 and CaClOH disappeared, and intensity of CaCO3 peaks increased. Finally, scanning electron microscopy analysis also indicated that the fly ash particles became more crystalline with agglomeration by further carbonation using ammonia. The process suggested in this study could be applied in the eco-industrial parks.

CO2 uptake performance and life cycle assessment of CaO-based sorbents prepared from waste oyster shells blended with PMMA nanosphere scaffolds

In this paper, we demonstrate a means of simultaneously solving two serious environmental issues by reutilization of calcinated mixture of pulverized waste oyster shells blending with poly(methyl methacrylate) (PMMA) nanospheres to prepare CaO-based sorbents for CO2 capture. After 10 cycles of isothermal carbonation/calcination at 750°C, the greatest CO2 uptake (0.19g CO2/g sorbent) was that for the sorbent featuring 70wt% of PMMA, which was almost three times higher than that (0.07g CO2/g sorbent) of untreated waste oyster shell. The greater CO2 uptake was likely a result of particle size reduction and afterwards surface basicity enhancement and an increase in the volume of mesopores and macropores. Following simplified life cycle assessment, whose all input values were collected from our experimental results, suggested that a significant CO2 emission reduction along with lesser human health and ecosystems impacts would be achieved immediately once waste is reutilized. Most importantly, the CO2 uptake efficiency must be greater than 20% or sorbents prepared from limestone mining would eventually produce a net positive CO2 emission.

CO<sub>2</sub> sequestration in plants: lesson from divergent strategies

Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis, which at the current atmospheric CO2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last half a century has shown that several plant species developed CO2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to algae, cyanobacteria and diatoms. Plants with C4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism (CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved efficiency of CO2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO2 could be an important approach to develop plants with efficient photosynthetic capacity.

Altitudinal variation of ecosystem CO2 fluxes in an alpine grassland from 3600 to 4200 m

Recent studies have recognized the alpine grasslands on the Qinghai–Tibetan plateau as a significant sink for atmospheric CO2. The carbon-sink strength may differ among grassland ecosystems at various altitudes because of contrasting biotic and physical environments. This study aims (i) to clarify the altitudinal pattern of ecosystem CO2 fluxes, including gross primary production (GPP), daytime ecosystem respiration (Redaytime) and net ecosystem production (NEP), during the period with peak above-ground biomass; and (ii) to elucidate the effects of biotic and abiotic factors on the altitudinal variation of ecosystem CO2 fluxes. Ecosystem CO2 fluxes and abiotic and biotic environmental factors were measured in an alpine grassland at four altitudes from 3600 to 4200 m along a slope of the Qilian Mountains on the northwestern Qinghai–Tibetan Plateau during the growing season of 2007. We used a closed-chamber method combined with shade screens and an opaque cloth to measure several carbon fluxes, GPP, Redaytime and NEP, and factors, light-response curve for GPP and temperature sensitivity of Redaytime. Above- and below-ground biomasses and soil C and N contents at each measurement point were also measured. (i) Altitudinal pattern of ecosystem CO2 fluxes: The maximum net ecosystem CO2 flux (NEPmax), i.e. the potential ecosystem CO2 sink strength, was markedly different among the four altitudes. NEPmax was higher at the highest and lowest sites, approximately −7.4 ± 0.9 and −6.7 ± 0.6 μmol CO2 m−2 s−1 (mean ± standard error), respectively, but smaller at the intermediate altitude sites (3800 and 4000 m). The altitudinal pattern of maximum gross primary production was similar to that of NEPmax. The Redaytime, however, was significantly higher at the lowest altitude (3.4 ± 0.3 μmol CO2 m−2 s−1) than at the other three altitudes. (ii) Altitudinal variation of vegetation biomass: The above-ground biomass was higher at the highest altitude (154 ± 27 g DW m−2) than at the other altitudes, which we attribute mainly to the large biomass in cushion plants at the highest altitude. The small above-ground biomass at the lower altitudes was probably due to heavy grazing during the growing season. (iii) Features of ecosystem CO2 fluxes: Redaytime and GPP were positively correlated with above-ground biomass. The low ratio of Redaytime to GPP at either the measurement point or the site level suggests that CO2 uptake efficiency tends to be higher at higher altitudes, which indicates a high potential sink strength for atmospheric CO2 despite the low temperature at high altitudes. The results suggest that the effect of grazing intensity on ecosystem carbon dynamics, partly by decreasing vegetation biomass, should be clarified further.

Impacts of aerosols and clouds on forest‐atmosphere carbon exchange

The impact of aerosols and clouds on CO2 uptake and water use efficiency at Harvard Forest has been studied by using collocated turbulent flux and radiation measurements. Measurements of a multifilter narrowband radiometer provide both direct and diffuse components of photosynthetically active radiation (PAR) by product integrals of synthesized spectra, with a normalized action spectrum for canopy photosynthesis. Optical properties of aerosols and clouds are also retrieved from the radiometer data. Optical properties of aerosols and clouds have significant impacts on photosynthesis not only through changes of the total amount of PAR but also through changes of its spectral distribution (or light quality) and its partitioning between direct and diffuse components. The diffuse PAR is much greater under patchy/thin cloud conditions than under aerosol conditions for a given optical depth. The “diffuse radiation use efficiency” coefficients are 3.40 and 1.95 for patchy/thin clouds and aerosols, respectively. Furthermore, the radiation use efficiency of CO2 uptake under clouds which completely block direct beam solar (optically thick clouds) is approximately 57 and 13% higher than under aerosol and patchy/thin clouds, respectively. The water use efficiency also showed significant enhancement as atmospheric conditions changed from aerosols, to patchy/thin clouds, and then to clouds opaque to direct solar radiation. Under optically thick cloud conditions the water use efficiency is almost 5 and 3 times greater than under aerosol and patchy/thin cloud conditions, respectively. These indicate that an increase of diffuse radiation may not be the only factor responsible for the enhancement of carbon assimilation under cloudy conditions. Changes in many other factors, such as temperature, moisture, latent heating, and precipitation, in the presence of clouds may have both direct and indirect influences on carbon assimilation.

Responses of Photosynthesis, Carbohydrates and Antioxidants in Needles of Norway Spruce to Slow and Rapid Changes in Ozone

Abstract:The goal of the present study was to examine the effects of slow and rapid changes of ozone (O3) concentrations on the physiological behaviour of current‐year needles of Norway spruce (Picea abies (L.) Karst.). For this purpose five‐year‐old spruce seedlings were exposed in growth chambers for 49 days to either charcoal‐filtered air, slowly increasing O3 concentrations from zero up to 100 nl I−1 in weekly steps of 25 nl I−1, or immediately to 100 nl I−1 of O3. During the investigation period gas exchange, carbohydrate and antioxidant contents of the current flush were measured. In needles which experienced slowly increasing O3 concentrations, cumulative O3 uptake was approximately 30 % lower than in needles continuously fumigated with 100 nl I−1 of O3. The higher 03 uptake in the permanent 100 nl I−1 O3 treatment caused a pronounced decline in net photosynthesis, in the efficiency of CO2 uptake and in the starch content of the seedlings. Initially the ascorbate pool increased, but after 5 weeks of exposure ascorbate concentrations declined and were comparable to values obtained in charcoal‐filtered controls, while the thiol contents were enhanced during fumigation with permanent 100 nl I‐−1 O3. On the contrary, slowly increasing O3 caused a significant increase in total needle ascorbate throughout the fumigation period, which probably prevented an O3‐induced decline in the photosynthetic machinery as photosynthesis was not affected although the thiol contents were not enhanced. Furthermore, starch content was slightly higher than in O3‐free controls. These results suggest that seedlings of Norway spruce have the possibility to acclimate to O3 stress, as slowly increasing O3 concentrations seemed to increase resistance and the seedlings were able to compensate.

Photosynthesis and photoinhibition in a tropical alpine giant rosette plant, Lobelia rhynchopetalum.

Carbodioxide uptake, oxygen evolution and chlorophyll fluorescence of leaves of Lobelia Lobelia rhynchopetalum Hemsl., a giant rosette plant of the tropical alpine regions of Ethiopia, were studied under field conditions at 4000 m above sea level. Our objective was to investigate the photosynthetic adaptation to the combination of wide fluctuation in diurnal temperature, high photon flux densities (PFD) and low CO2 partial pressure encountered in these regions. At an ambient CO2 partial pressure of c. 17 Pa, maximal rates of CO2 uptake were low, ranging between 4 and 6 μmol m-2 s-1 . Such rates, however, required high PFDs and were observed only at levels of 1500 μmol photons m-2 s-2 . Carbon dioxide uptake was significantly inhibited when PFD was ≤ 2000 μmol photons m-2 s-1 . On the other hand, at saturating CO2 levels, maximal photosynthetic oxygen evolution was higher (30 μmol C2 m-2 s-1 ). saturating at the same PFD as CO2 uptake. Quantum efficiency of CO2 uptake (0.006 mol CO2 mol photons-1 , at high altitude and a low CO, partial pressure of 17 Pa) and even of oxygen evolution under CO2 -saturating conditions in the leaf O2 electrode (0.05 mol O2 mo) photons-1 ) indicated reduced photosynthetic efficiency. Electron transport rate (ETR) was strongly correlated with the leaf temperature. Non-photochemical quenching (NPQ) responded inversely to leaf temperature and stomatal conductance. The results indicated that in the morning, when the sun irradiates the partly frozen leaves with closed stomata, NPQ is the principal mechanism by which Lobelia leaves protect their photosynthetic apparatus. However, during the day, the predominant upright inclination of the leaves significantly contributes to protecting the leaves from excess light absorption. A comparison of the chlorophyll fluorescence of young and old leaves revealed that the former had high ETR and quantum efficiency of photosynthetic electron transport but a lower capacity for NPQ. Extremely high NPQ values but low ETR and low quantum efficiency were recorded for the old leaves. Thus, in the course of maturation the leaves apparently lose photosynthetic efficiency but increase their capability for protective non-photochemical quenching.

Evidence that Plants from High Altitudes Retain their Greater Photosyntheti Efficiency Under Elevated CO 2

Herbaceous plant species native to low and high altitudes in the Alps evolved under CO 2 partial pressures (P a ) that differ as much as pre-industrial P a differs from present day P a at low altitude (e.g. 21% for a 2000-m difference in altitude). In a previous study we showed that the efficiency of CO 2 uptake (ECU) in typical high-altitude species is generally greater than in low-altitude species. Here we investigate whether this difference prevails under longer-term exposure to altered P a . Alpine and lowland species (mainly Ranunculus glacialis/R. acris and Geum reptans/G. rivale) were grown under various CO 2 regimes in full daylight growth chambers at their respective natural growth temperature and photoperiod (...)

Exposure of mature Norway spruce to ozone in twig-chambers: effects on gas exchange

SynopsisLittle is known about ozone (O3) effects on adult trees in the field, where ecophysiological parameters control pollutant uptake. It was the goal of this study to examine how ambient and above ambient O3 concentrations affect gas exchange of mature Norway spruce (Picea abies (L.) Karst.). Therefore, twigs were enclosed in chambers and exposed to different O3 concentrations for one and two seasons over three years. During winter periods twigs were maintained under ambient conditions. Data from the shade crown of spruce trees at 1000 m a.s.l. are presented. After one and two fumigation periods no clear treatment effects on gas exchange were observed in twigs fumigated with O3 concentrations ranging from zero up to ambient (A) + 60 ppb. However, O3 at 90 ppb reduced photosynthesis and conductance. CO2 response curves indicated that in A + 90 twigs the efficiency of CO2 uptake was diminished. Observed losses in Pn of A + 90 twigs were greater than reductions in conductance indicating that stomatal closure alone did not limit CO2 uptake. We conclude that ambient and slightly above ambient O3 concentrations do not alter gas exchange of mature Norway spruce. Therefore, suppositions on O3 damage on mature spruce trees should be critically questioned.

Carbon Isotopes in Photosynthesis

he efficiency of photosynthesis continues to interest biochemists, biologists, and plant physiologists. Scientists interested in CO2 uptake are concerned about the extent to which the uptake rate is limited by such factors as stomatal diffusion and the chemistry of the CO2 absorption process. The fractionation of carbon isotopes that occurs during photosynthesis is one of the most useful techniques for investigating the efficiency of CO2 uptake. Atmospheric carbon dioxide contains approximately 1.1% of the nonradioactive isotope carbon-13 and 98.9% of carbon-12. During photosynthesis, plants discriminate against C because of small differences in chemical and physical properties imparted by the difference in mass. This discrimination can be used to assign plants to various photosynthetic groups. The isotope fractionation also reflects limitations on photosynthetic efficiency imposed by the various diffusional and chemical components of CO2 uptake. When analyzed in detail, this fractionation provides information .about water use efficiency and indicates that different strategies are needed for improving wateruse efficiency in different kinds of plants. Isotope fractionation in simple physical and chemical processes is well understood and is commonly Current studies include