Stomatal conductance, photosynthesis and respiration of temperate deciduous tree seedlings grown outdoors at an elevated concentration of carbon dioxide

Seedlings of temperate deciduous tree species were grown outdoors at ambient and at an elevated concentration of carbon dioxide to examine how aspects of their gas exchange would be altered by growth at elevated carbon dioxide concentration. Leaf conductances to water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole-plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm³ m^?3 carbon dioxide did not differ from that of plants grown and measured at 350 cm³ m^?3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33°C. Photo-synthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of mass when grown and measured at elevated carbon dioxide concentration.     

Isotopic and chemical investigations of Fe (III) reduction by Shewanella putrefaciens strain 200R

Experiments were conducted using the Fe⁺³‐reducing bacterium Shewanella putrefaciens strain 200R to determine the stable carbon isotope fractionation during dissimilatory Fe (III) reduction and associated lactate oxidation at circum‐neutral pH. Previous studies used equilibrium fractionation factors (~14.3‰) between bacterial biomass and synthesized fatty acids to identify the predominant carbon fixation pathways for some of the most frequently isolated microbes including Shewanella under anaerobic conditions. We investigated the carbon isotope disproportionation among organic carbon substrate (lactate), biomass and respired carbon dioxide at the lag to stationary phase of the growth curve. Ferric citrate and sodium lactate were used as electron acceptor and donor, respectively. Sodium bicarbonate or potassium phosphate was used as buffering agent. Iron (II), iron (III), dissolved inorganic carbon (DIC) and carbon isotope ratios were measured for both bicarbonate‐ and phosphate‐buffered systems. Carbon isotope ratio measurements were made on the respired CO₂ (as DIC) and microbial biomass for both buffering conditions. The fraction of lactate consumed was estimated using DIC as a proxy and was verified by direct measurement using HPLC. Our result showed that bicarbonate‐buffered system has an enhancing effect in the reduction process compared to the phosphate system. Both systems resulted in carbon isotope fractionations between the lactate substrate and DIC that could be modelled as a Rayleigh process. The biomass produced under both buffer conditions was depleted on average by ~2‰ relative to the substrate and enriched by ~5‰ relative to the DIC. This translates to an overall isotopic fractionation of 10–12‰ between the biomass and respired CO₂ in both buffering systems.     

Ternary effects on the gas exchange of isotopologues of carbon dioxide

The ternary effects of transpiration rate on the rate of assimilation of carbon dioxide through stomata, and on the calculation of the intercellular concentration of carbon dioxide, are now included in standard gas exchange studies. However, the equations for carbon isotope discrimination and for the exchange of oxygen isotopologues of carbon dioxide ignore ternary effects. Here we introduce equations to take them into account. The ternary effect is greatest when the leaf-to-air vapour mole fraction difference is greatest, and its impact is greatest on parameters derived by difference, such as the mesophyll resistance to CO(2) assimilation, r(m) . We show that the mesophyll resistance to CO(2) assimilation has been underestimated in the past. The impact is also large when there is a large difference in isotopic composition between the CO(2) inside the leaf and that in the air. We show that this partially reconciles estimates of the oxygen isotopic composition of CO(2) in the chloroplast and mitochondria in the light and in the dark, with values close to equilibrium with the estimated oxygen isotopic composition of water at the sites of evaporation within the leaf.     

The Diffusion of Oxygen, Carbon Dioxide, and Inert Gas in Flowing Blood

Measurements were made of exchange rates of oxygen, carbon dioxide, and krypton-85 with blood at 37.5°C. Gas transfer took place across a 1 mil silicone rubber membrane. The blood was in a rotating disk boundary layer flow, and the controlling resistance to transfer was the concentration boundary layer. Measured rates were compared with rates predicted from the equation of convective diffusion using velocities derived from the Navier-Stokes equations and diffusivities calculated from the theory for conduction in a heterogeneous medium. The measured absorption rate of krypton-85 was closely predicted by this model. Significant deposition of material onto the membrane surface, resulting in an increased transfer resistance, occurred in one experiment with blood previously used in a nonmembrane type artificial lung. The desorption rate of oxygen from blood at low P_o2¹ was up to four times the corresponding transfer rate of inert gas. This effect is described somewhat conservatively by a local equilibrium form of the convective diffusion equation. The carbon dioxide transfer rate in blood near venous conditions was about twice that of inert gas, a rate significantly greater than predicted by the local equilibrium theory. It should be possible to apply these theoretical methods to predict exchange rates with blood flowing in systems of other geometries.     

Biological fractionation of stable carbon isotopes at the aerobic/anaerobic water interface of meromictic water bodies

Mass-spectrometric investigation of carbon isotope composition (δ¹³C) was carried out for suspended organic matter and dissolved mineral compounds for the water column of some meromictic water bodies differing in salinity and trophic state. As a rule, a more pronounced carbon isotope fractionation (resulting from the metabolism of phytoplankton and anoxygenic phototrophic bacteria) was revealed in the zones of enhanced oxygenic and anoxygenic photosynthesis. Carbon isotope fractionation at the border between oxidized and reduced waters depends both on the activity of microbial communities and on the dominant species of phototrophic microorganisms. Analysis of the distribution profiles of the isotopic composition of suspended organic matter and dissolved mineral carbon revealed active mineralization of the organic matter newly formed via anoxygenic photosynthesis in the monimolimnion by microbial communities, resulting in the release of isotopically light carbon dioxide. Mineral carbon in the anaerobic zones of highly productive meromictic water bodies is therefore enriched with the light ¹²C isotope.     

Ecosystem-atmosphere CO(2) exchange: interpreting signals of change using stable isotope ratios

Changes in the concentration and stable isotope ratio of atmospheric CO(2) can be used to study variations in the net exchange of carbon dioxide in terrestrial ecosystems (net difference between total photosynthesis and respiration). Changes in the timing of seasonal fluctuations in atmospheric CO(2) concentration have suggested that net uptake of carbon dioxide has been increasing in northern latitude ecosystems in association with warmer temperatures and a lengthening of the growing season. Stable isotope techniques allow a more detailed separation of differences between ecosystem photosynthesis and respiration because these two processes have contrasting effects on both the carbon and oxygen isotope ratio of atmospheric CO(2). Future applications of stable isotope analyses include documenting and monitoring the influence of global environmental change on ecosystem CO(2) exchange at regional scales (10-1000km(2)).     

Subsurface characterization of methane production and oxidation from a New Hampshire wetland

We measured the carbon isotopic composition of pore water carbon dioxide from Sallie’s Fen, a New Hampshire poor fen. The isotope profiles are used in combination with a one‐dimensional diffusion–reaction model to calculate rates of methane production, oxidation and transport over an annual cycle. We show how the rates vary with depth over a seasonal cycle, with methane produced deeper during the winter months and at progressively shallower depths into the summer season. The rates of methane production, constrained by the measured δ¹³C_dic profiles, cannot explain high methane emission during the summer. We suggest that much of the methane produced during this time comes either from the unsaturated peat, or from the top 1–3 cm of saturated peat where episodic exchange with the atmosphere makes it invisible to our method.     

Fractionation of Stable Carbon Isotopes during Chemoautotrophic Growth of Sulfur-Oxidizing Bacteria

Laboratory-grown strains of chemoautotrophic Thiomicrospira sp. strain L-12 and Thiobacillus neapolitanus produced cell carbon that was 24.6 to 25.1 ppt (24.6 to 25.1 mg/g) lower in ¹³C isotope abundance than the ambient source of carbon dioxide and bicarbonate. This degree of ¹³C isotope depletion was comparable to that found in organic material produced in deep-sea hydrothermal-vent communities.     

Isotope exchange reactions with radiolabeled sulfur compounds in anoxic seawater

The isotope exchange between³⁵S-labeled sulfur compounds of sulfate (SO₄ ^2–), elemental sulfur (S⁰), polysulfide (S_n ^2–), hydrogen sulfide (HS^–: H₂S + HS^– + S^2–), iron sulfide (FeS), and pyrite (FeS₂) was studied at pH 7.6 and 20 °C in anoxic, sterile seawater. Isotope exchange was observed between S⁰, S₂ ^2– HS^–, and FeS, but not between³⁵S labeled SO₄ ^2– or FeS₂ and the other sulfur compounds. Polysulfide mediated the isotope exchange between S⁰ and bisulfide (HS^–). The isotope exchange between S⁰ and S_n ^2–) reached 50% of equilibrium within < 2 min while exchange between S₂ ^2– and HS^– approached equilibrium within 0.5-1 h. In all the experiments HS^–, revealed a fraction exchange from 0.79 to 1.00. Isotope exchange between S^2– and FeS took place only via S₂ ^2– and/or HS^–. The isotope exchange between iron sulfide and the other sulfur compounds was not complete within 24 h as shown by a fraction exchange of 0.07–0.83. This lack of equilibrium (fraction exchange < 1) was due to the isotope exchange between dissolved compounds and surfaces of sulfur particles. The isotopic exchange reactions limit the usefulness of radiotracers in process studies of the inorganic sulfur species. Exchange reactions will also affect the stable isotope distribution among the sulfur species. The kinetics of the isotopic exchange reactions, however, depend on both pH and temperature.     

A simple procedure for the synthesis of [32P]phosphoenolpyruvate via the pyruvate kinase exchange reaction at equilibrium

A one step procedure is presented for the preparation of [³²P]phosphoenolpyruvate from [γ-³²P]ATP using pyruvate kinase. The reaction is carried out at chemical equilibrium and involves only an exchange of isotope between ATP and phosphoenolpyruvate. The initial phosphoenolpyruvate/ATP ratio in the reaction mixture determines the degree of ³²P incorporation into phosphoenolpyruvate when isotopic equilibrium is achieved.     

The role of <Emphasis Type="Italic">Salvelinus</Emphasis> in contemporary studies of evolution,trophic ecology and anthropogenic change

The aim of this study was to better understand the relations between carbon and oxygen stable isotope values of ambient water, mollusc shells, macrophytes and their carbonate encrustations, commonly used in palaeolimnological studies. Water, molluscs and macrophytes were sampled from the littoral zone in Lake Lednica, NW Poland. The influence of carbon species assimilated during photosynthesis and the net intensity of photosynthesis resulting from the size of charophyte species and the density of their stands were postulated to be the most important factors causing the species-specific δ¹³C values of charophyte thalli and encrustations. It was suggested that photosynthetic activity of charophytes affected not only the δ¹³C values of charophyte encrustations but also mollusc shells by changing δ¹³C values of DIC within charophyte stands. In addition, incorporation of metabolic carbon into the shell was proposed as the main cause of both the ¹³C depletion of mollusc shells relative to δ¹³C values of DIC and the species-specific δ¹³C values of shells. Mollusc shells were precipitated at the isotope equilibrium or close to the equilibrium with δ¹⁸O values of lake water. Charophyte encrustations were found to be ¹⁸O depleted due to the kinetic isotope effects during intense photosynthesis and thus fast precipitation of the calcite.     

Carbon dioxide exchange in a high-arctic fen estimated by eddy covariance measurements and modelling

The high-arctic environment is an environment where the consequences of global warming may be significant. In this paper we report on findings on carbon dioxide and water vapour fluxes above a sedge-dominated fen at Zackenberg (74°28′N, 20°34′ W) in The National Park of North and East Greenland. Eddy covariance measurements were initiated at the start of the growing season and terminated shortly before its end lasting 45 days. The net CO₂ flux during daytime reaches a high of 10 μmol m^–2s^–1, and around the summer solstice, net CO₂ assimilation occurred at midnight, resulting in net carbon gain during the night. The measured carbon dioxide fluxes compare well to estimates based on the photosynthesis model by Collatz et al. (1991 ). The total growing-season net ecosystem CO₂ exchange was estimated to be 96 g C m^–2 based on the carbon dioxide model and micrometeorological data. Finally, the combined CO₂ assimilation and soil respiration models are used for examining the dependence of the carbon dioxide budget on temperature. The ecosystem is found to function optimally given the present temperature conditions whereas either an increase or a decrease in temperature would reduce the ecosystem CO₂ accumulation. An increase in temperature by 5 °C would turn the ecosystem into a carbon dioxide source.     

Use of Carbon Isotope Composition for Characterization of Microbial Activity in Arable Soils

The effect of glucose on microbial mineralization of soil organic matter (SOM) was studied in arable soil specimens. The fluxes of carbon dioxide generated during this degradation were deduced from differences in the carbon isotope abundance ratios of glucose δ¹³C = –11.4 per mil) and SOM δ¹³C = –27.01 per mil). The priming effect of glucose and respiratory quotient (RQ) were taken as indices of activation of SOM-consuming microbiota. The data on microbial mineralization of organic matter in soil obtained in this study show that the addition of a readily consumable substance (glucose) to soil favors SOM degradation and increases the release of carbon dioxide from soil to atmosphere.     

Variation and inheritance of carbon isotope discrimination in wheat (Triticum aestivum)

Significant small variations exist in the proportion of the heavy isotope (¹³C) in organic and inorganic materials. The amounts of variations depend on the discrimination against or (in favor of) the heavy isotope through equilibrium reactions or kinetic processes particularly during CO₂ fixation in plants. These variations have also paved the way to measure carbon isotope discrimination in plant materials as a surrogate for water-use efficiency. Thus looking for variation and understanding the inheritance of this character is a prerequisite for improving wheat genotypes showing high water use efficiency and tolerance to drought. The main objectives of this review is to provide an overview of various aspects in which inheritance of ? is documented and of variation for carbon isotope discrimination reported in wheat under different circumstances. The relationship between carbon isotope discrimination and drought tolerance is also discussed exclusively in wheat.     

Effect of high atmospheric CO2 concentration on δ13 of algae

Precambrian reduced carbon is more depleted in¹³C than what would be expected from the carbon isotopic composition of modern marine algae and algal mats. Since the photosynthetic carbon fixation by algae is the most likely source of the reduced carbon, the depletion has been considered an anomaly.We examined factors that might have contributed to the carbon isotope fractionation from inorganic sources through algae to organic matter in a sedimentary rock, and related laboratory obtainable data to those from Precambrian rocks. Laboratory culture experiments were then performed with nine strains of algae at various concentrations of carbon dioxide, and the result was interpreted according to the relationship.It indicated that the depletion could be understood in terms of a combined effect of fractionation factors, most depletion occurring at the fractionation during the photosynthetic carbon fixation. It also suggested that all but one algal strain incorporated bicarbonate as the source of carbon for its growth. The exception was a thermophilic, acidophilic alga, which must have used carbon dioxide as the carbon source.The present study suggests that Precambrian atmosphere was enriched in carbon dioxide roughly two orders of magnitude more than its present atmospheric level.     

Fluxes of carbon dioxide and water vapor above paddy fields

Atmospheric fluxes of carbon dioxide and water vapor were measured by the eddy correlation technique over a paddy field in 1989. The carbon dioxide was transported downward during daylight hours due to photosynthesis of the paddy crop. The downward flux of carbon dioxide increased with increasing net radiation. Maximum values of downward flux varied with the growing stage of the paddy crop: ca. 0.3 mg m^–2 s^–1 at early vegetative growth stage and ca. 1.3 mg m^–2 s^–1 at ear formation stage. The daytime totals of downward flux of carbon dioxide also showed seasonal variation reflecting the photosynthetic activity of the paddy crop: ca. 6 g m^–2 at early vegetative growth stage in June and 40 g m^–2 at ear formation stage in September. The seasonal variation of daily totals of carbon dioxide flux shows that carbon dioxide of about 28 t ha^–1 is fixed by the paddy crop from transplanting to harvesting. Taking into account the water use efficiency, the paddy crop requires water in amounts at least 100 times that of carbon dioxide fixed by photosynthesis. It is noted that the correlation coefficients between carbon dioxide, water vapor and vertical wind velocity have constant values under near neutral and free convective regimes.     

Comparison of water-use efficiency and internal leaf carbon dioxide concentration in juvenile leaves and phyllodes of Acacia koa (leguminosae) from Hawaii,estimated by two methods

To gain further insight into comparative ecophysiology of different leaf types, water-use efficiency (WUE) and internal leaf carbon dioxide concentration (C_i) were estimated in the field for juvenile leaves and phyllodes of Acacia koa by carbon dioxide and water vapor exchange using a closed system infrared gas analyzer and humidity sensor, and by δ¹³C measurements. Both methods indicate that phyllodes possessed higher WUE and lower C_i than juvenile leaves. However, C_i predicted by δ¹³C for juvenile leaves and phyllodes was lower than the average gas exchange estimated values of C_i and closer to minimal gas exchange estimated values of C_i. It is suggested that δ¹³C may be influenced more during times of maximal assimilation and leaf expansion than during maintenance.     

Measurement of Distribution of Photosynthesis in Plant Canopies

ATTEMPTS have been made to measure or calculate photosyn-thetic activity in various morphological parts or height layers of plant canopies. This has been done by measuring dry weight changes in relation to removal of the parts¹, carbon dioxide exchange when the parts were enclosed in assimilation chambers² and a combination of progressive defoliation and whole canopy carbon dioxide uptake measurement^3,4. To study the activity in layers of the canopy, Leach and Watson⁵ placed phytometers at various points in the canopy to stimulate the photosynthesis of adjacent plant parts and aerodynamic methods have since been used to estimate the distribution of photosynthesis in canopies⁶. By using photosynthesis response data for leaves and information about the environment in the profile, Monsi and Saeki⁷ and others^8,9 have estimated localized photosynthesis.     

Exchange of CO2, CH4 and N2O between the atmosphere and two northern boreal ponds with catchments dominated by peatlands or forests

Concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the water column and their exchange at the water/air interface were studied during the open water period in two freshwater ponds with different catchment characteristics in the northern boreal zone in Finland; either peatlands or coniferous upland forests dominated the catchment of the ponds. Both ponds were supersaturated with dissolved CO₂ and CH₄ with respect to the equilibrium with the atmosphere, but were close to the equilibrium with N₂O. The mean CO₂ efflux from the pond was higher in the peatland-dominated catchment (22 mg m^–2 h^–1) than in the forested catchment (0.7 mg m^–2 h^–1), whereas the mean CH₄ emissions were similar (7.6 and 3.5 mg m^–2 d^–1, respectively). The fluxes of N₂O were generally negligible. The higher CO₂ concentrations and efflux in the pond with the peatland-dominated catchment were attributed to a greater input of allochthonous carbon to that pond from its catchment due to its higher water colour and higher total organic carbon (TOC) concentration. The water pH, which also differed between the ponds, could additionally affect the CO₂ dynamics. Since the catchment characteristics can regulate aquatic carbon cycles, catchment-scale studies are needed to attain a deeper understanding of the aquatic greenhouse gas dynamics.     

CO2 in large-scale and high-density CHO cell perfusion culture

Productivity in a CHO perfusion culture reactor was maximized when pCO₂ was maintained in the range of 30–76 mm Hg. Higher levels of pCO₂ (> 150 mm Hg) resulted in CHO cell growth inhibition and dramatic reduction in productivity. We measured the oxygen utilization and CO₂ production rates for CHO cells in perfusion culture at 5.55×10^-17 mol cell^-1 sec^-1 and 5.36×10^-17 mol cell^-1 sec^-1 respectively. A simple method to directly measure the mass transfer coefficients for oxygen and carbon dioxide was also developed. For a 500 L bioreactor using pure oxygen sparge at 0.002 VVM from a microporous frit sparger, the overall apparent transfer rates (k_La+k_AA) for oxygen and carbon dioxide were 0.07264 min^-1 and 0.002962 min^-1 respectively. Thus, while a very low flow rate of pure oxygen microbubbles would be adequate to meet oxygen supply requirements for up to 2.1×10⁷ cells/mL, the low CO₂ removal efficiency would limit culture density to only 2.4×10⁶ cells/mL. An additional model was developed to predict the effect of bubble size on oxygen and CO₂ transfer rates. If pure oxygen is used in both the headspace and sparge, then the sparging rate can be minimized by the use of bubbles in the size range of 2–3 mm. For bubbles in this size range, the ratio of oxygen supply to carbon dioxide removal rates is matched to the ratio of metabolic oxygen utilization and carbon dioxide generation rates. Using this strategy in the 500 L reactor, we predict that dissolved oxygen and CO₂ levels can be maintained in the range to support maximum productivity (40% DO, 76 mm Hg pCO₂) for a culture at 10⁷ cells/mL, and with a minimum sparge rate of 0.006 vessel volumes per minute.A = volumetric agitated gas-liquid interfacial area at the top of the liquid, 1/mB = cell broth bleeding rate from the vessel, L/minCER = carbon dioxide evolution rate in the bioreactor, mol/min[CO₂] = dissolved CO₂ concentration in liquid, M[CO₂]^* = CO₂ concentration in equilibrium with sparger gas, M[CO₂]^** = CO₂ concentration in equilibrium with headspace gas, MCO₂(1) = dissolved carbon dioxide molecule in water[C_T] = total carbonic species concentration in bioreactor medium, M[C_T]_F = total carbonic species concentration in feed medium, MD = bioreactor diameter, mD_I = impeller diameter, mD_b = the initial delivered bubble diameter, mF = fresh medium feeding rate, L/minH_L = liquid height in the vessel, mk_A = carbon dioxide transfer coefficient at liquid surface, m/mink _infA ^supO = oxygen transfer coefficient at liquid surface, m/minNomenclature