Accumulation of eicosapentaenoic acid in <Emphasis Type="Italic">Nannochloropsis</Emphasis> sp. in response to elevated CO<Subscript>2</Subscript> concentrations

To increase eicosapentaenoic acid (EPA, 20:5, n-3) content in the marine alga Nannochloropsis sp., the effect of CO₂ concentration during cultivation has been investigated. In a batch culture under normal atmospheric conditions (0.037% CO₂), the EPA content per cell increased during the first 1.5 days and then decreased immediately even though the cells were in an exponential growth phase. Increasing the CO₂ concentration to 0.3% and 2% over day 1.5 retained the EPA content at the higher concentration for another 1 and 2 days, respectively, suggesting that the EPA accumulation is enhanced by elevated concentrations of CO₂. EPA accumulation in response to elevated CO₂ concentrations was also observed during a later growth phase when CO₂ was introduced after the decrease of EPA content. The addition of CO₂ caused a slight decrease in the pH of the medium though this was not the cause of the observed EPA accumulation as addition of acidic buffer did not affect the EPA content. The maximum EPA production was obtained when 2% CO₂ was supplied 12 h prior to the end of the exponential growth. The total EPA production during 4-day cultivation was about twice that obtained with ambient air. These results suggest that the available CO₂ concentration affects the EPA content in Nannochloropsis sp.     

Immersion in CO<Subscript>2</Subscript>-rich water containing NaCl diminishes blood pressure fluctuation in anesthetized rats

Remarkably, bathing in hot springs containing high concentrations of carbon dioxide (CO₂) influences cardiovascular function more than bathing in fresh water. The CO₂-enriched water in hot springs generally contains many salts, whose interactions remain unknown. We separately evaluated the actions of individual factors in CO₂-enriched water and confirmed that CO₂ and NaCl have combined effects on blood pressure fluctuations in anesthetized rats. Animals equipped with sensor probes to monitor body temperature, skin blood flow and arterial blood pressure were immersed in bathwater (35°C) containing CO₂ with NaCl, KCl or sucrose. The effects of these factors on cardiovascular function were evaluated using power-spectral analysis of fluctuations in blood pressure and heart rate. Compared with immersion in tap water, heart rate and skin vascular resistance were reduced during immersion in CO₂-enriched water irrespective of the presence of other components. In terms of the very low frequency range (0.02–0.195 Hz), the power of blood pressure fluctuation during immersion was significantly reduced when the CO₂-enriched water contained more than 1.5% NaCl but was not influenced by other components of similar osmotic pressure and the same specific gravity. The results indicated that the coexistence of CO₂ and sodium ions in bathwater reduce blood pressure fluctuations, and suggested that this combination effect of CO₂ and salt contributes to the sedative effect on human cardiovascular functions while bathing in CO₂-hot springs.     

The interacting effects of elevated atmospheric CO<Subscript>2</Subscript> concentration,drought and leaf-to-air vapour pressure deficit on ecosystem isoprene fluxes

Isoprene is the most abundant biogenic hydrocarbon released from vegetation and it plays a major role in tropospheric chemistry. Because of its link to climate change, there is interest in understanding the relationship between CO₂, water availability and isoprene emission. We explored the effect of atmospheric elevated CO₂ concentration and its interaction with vapour pressure deficit (VPD) and water stress, on gross isoprene production (GIP) and net ecosystem exchange of CO₂ (NEE) in two Populus deltoides plantations grown at ambient and elevated atmospheric CO₂ concentration in the Biosphere 2 Laboratory facility. Although GIP and NEE showed a similar response to light and temperature, their responses to CO₂ and VPD were opposite; NEE was stimulated by elevated CO₂ and depressed by high VPD, while GIP was inhibited by elevated CO₂ and stimulated by high VPD. The difference in response between isoprene production and photosynthesis was also evident during water stress. GIP was stimulated in the short term and declined only when the stress was severe, whereas NEE started to decrease from the beginning of the experiment. This contrasting response led the carbon lost as isoprene in both the ambient and the elevated CO₂ treatments to increase as water stress progressed. Our results suggest that water limitation can override the inhibitory effect of elevated CO₂ leading to increased global isoprene emissions in a climate change scenario with warmer and drier climate.     

Soil CO<Subscript>2</Subscript> flux affected by <Emphasis Type="Italic">Aporrectodea caliginosa</Emphasis> earthworms

The effects of Aporrectodea caliginosa earthworms on both carbon dioxide (CO₂) accumulation in and emissions from soil, as well as the simultaneous impact of earthworms on soil microbiological properties were investigated in a microcosm experiment carried out over 5.5 months. Concentration of CO₂ in soil air was greater at a depth of 15 cm when compared with a depth of 5 cm, but varied during the season both in control and earthworm-inhabited chambers. Peaks of CO₂ concentrations at both depths occurred in both treatments during August, approximately 80 days after the experiment started. Generally, the presence of earthworms increased the CO₂ concentration at 15-cm depth. Larger CO₂ emissions were consistently recorded in conjunction with higher amounts of CO₂ in soil air when chambers were inhabited by earthworms. The total CO₂ emissions during the experimental period covering 161 days were estimated at 118 g CO₂-C m⁻² and 99 g CO₂-C m⁻² from chambers with and without earthworms respectively. Moreover, the presence of earthworms increased microbial biomass in the centre and at the bottom of chambers, and enhanced both dehydrogenase activity and nitrifying enzyme activity in the soils. We suggest that the effect of earthworms on both the enhanced soil accumulation of CO₂ as well as emissions of CO₂ was mostly indirect, due to the impacts of earthworms on soil microbial community.     

CO2‐metabolism in early tetrapods revisited: inferences from osteological correlates of gills,skin and lung ventilation in the fossil record

One of the most important physiological changes during the conquest of land by vertebrates was the increasing reliance on lung breathing, with the concomitant decrease in importance of gill breathing. The main problem involved here was to cope with the excessive accumulation of CO₂ in the body and to avoid respiratory acidosis. In the past, several often mutually contradicting hypotheses of CO₂‐elimination via skin, lungs and gills in early tetrapods have been proposed, based on theoretical physiological considerations and comparison with extant air‐breathing fishes and amphibians. This study proposes a revised scenario of CO₂‐elimination in early tetrapods based on fossil evidence, that is recently identified osteological correlates of gills, skin structure and mode of lung ventilation. In stem tetrapods of the Devonian and Carboniferous, O₂‐uptake via the lungs by buccal pumping was decoupled from CO₂‐release via internal gills, and the rather gas‐impermeable skin played a minor role in gaseous exchange. The two main lineages of crown‐group tetrapods, the amphibian and amniote lineage, used different strategies of CO₂‐elimination. As in stem tetrapods, O₂‐uptake and CO₂‐release remained always largely decoupled in temnospondyls, which ventilated their lungs via buccal pumping and relied mainly on their internal gills for CO₂‐release. Temnospondyls were not able to reduce their internal gills before their skin became more gas permeable and their body size was reduced, to shift from internal gills to the skin as the major site of CO₂‐elimination, a pattern that is retained in most lissamphibians. In contrast, internal gills were lost very early in stem amniote evolution. This was associated with the evolution of the more effective aspiration pump that allowed the elimination of the bulk of CO₂ via the lungs, leading to a coupled O₂‐uptake and CO₂‐loss in stem amniotes and later in amniotes.     

Effect of elevated CO<Subscript>2</Subscript> levels on leaf starch,nitrogen and photosynthesis of plants growing at three natural CO<Subscript>2</Subscript> springs in Japan

Plant communities around natural CO₂ springs have been exposed to elevated CO₂ levels over many generations and give us a unique opportunity to investigate the effects of long-term elevated CO₂ levels on wild plants. We searched for natural CO₂ springs in cool temperate climate regions in Japan and found three springs that were suitable for studying long-term responses of plants to elevated levels of CO₂: Ryuzin-numa, Yuno-kawa and Nyuu. At these CO₂ springs, the surrounding air was at high CO₂ concentration with no toxic gas emissions throughout the growth season, and there was natural vegetation around the springs. At each site, high-CO₂ (HC) and low-CO₂ (LC) plots were established, and three dominant species at the shrub layers were used for physiological analyses. Although the microenvironments were different among the springs, dicotyledonous species growing at the HC plots tended to have more starch and less nitrogen per unit dry mass in the leaves than those growing at the LC plots. In contrast, monocotyledonous species growing in the HC and LC plots had similar starch and nitrogen concentrations. Photosynthetic rates at the mean growth CO₂ concentration were higher in HC plants than LC plants, but photosynthetic rates at a common CO₂ concentration were lower in HC plants. Efficiency of water and nitrogen use of leaves at growth CO₂ concentration was greatly increased in HC plants. These results suggest that natural plants growing in elevated CO₂ levels under cool temperate climate conditions have down-regulated their photosynthetic capacity but that they increased photosynthetic rates and resource use efficiencies due to the direct effect of elevated CO₂ concentration.     

The effects of elevated atmospheric CO<Subscript>2</Subscript> and nitrogen amendments on subsurface CO<Subscript>2</Subscript> production and concentration dynamics in a maturing pine forest

Profiles of subsurface soil CO₂ concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and 2006 in 16 locations at the free air CO₂ enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO₂ concentration levels (ambient [CO₂]^a, ambient + 200 ppmv, [CO₂]^e) and two soil nitrogen (N) deposition levels (ambient, ambient + fertilization at 11.2 g_N m⁻² year⁻¹). The combination of these measurements permitted indirect estimation of belowground CO₂ production and flux profiles in the mineral soil. Adjacent to the soil CO₂ profiles, direct (chamber-based) measurements of CO₂ fluxes from the soil–litter complex were simultaneously conducted using the automated carbon efflux system. Based on the measured soil CO₂ profiles, neither [CO₂]^e nor N fertilization had a statistically significant effect on seasonal soil CO₂, CO₂ production, and effluxes from the mineral soil over the study period. Soil moisture and temperature had different effects on CO₂ concentration depending on the depth. Variations in CO₂ were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface (within the first 10 cm), where CO₂ pulses were induced by rainfall events. The soil effluxes were equal to the CO₂ production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from the CO₂ profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests that a better parameterization of the soil CO₂ diffusivity is required for these soil moisture extremes.     

Long-term effects of elevated atmospheric CO<Subscript>2</Subscript> on species composition and productivity of a southern African C<Subscript>4</Subscript> dominated grassland in the vicinity of a CO<Subscript>2</Subscript> exhalation

We describe the long-term effects of a CO₂ exhalation, created more than 70 years ago, on a natural C₄ dominated sub-tropical grassland in terms of ecosystem structure and functioning. We tested whether long-term CO₂ enrichment changes the competitive balance between plants with C₃ and C₄ photosynthetic pathways and how CO₂ enrichment has affected species composition, plant growth responses, leaf properties and soil nutrient, carbon and water dynamics. Long-term effects of elevated CO₂ on plant community composition and system processes in this sub-tropical grassland indicate very subtle changes in ecosystem functioning and no changes in species composition and dominance which could be ascribed to elevated CO₂ alone. Species compositional data and soil δ¹³C isotopic evidence suggest no detectable effect of CO₂ enrichment on C₃:C₄ plant mixtures and individual species dominance. Contrary to many general predictions C₃ grasses did not become more abundant and C₃ shrubs and trees did not invade the site. No season length stimulation of plant growth was found even after 5 years of exposure to CO₂ concentrations averaging 610 μmol mol⁻¹. Leaf properties such as total N decreased in the C₃ but not C₄ grass under elevated CO₂ while total non-structural carbohydrate accumulation was not affected. Elevated CO₂ possibly lead to increased end-of-season soil water contents and this result agrees with earlier studies despite the topographic water gradient being a confounding problem at our research site. Long-term CO₂ enrichment also had little effect on soil carbon storage with no detectable changes in soil organic matter found. There were indications that potential soil respiration and N mineralization rates could be higher in soils close to the CO₂ source. The conservative response of this grassland suggests that many of the reported effects of elevated CO₂ on similar ecosystems could be short duration experimental artefacts that disappear under long-term elevated CO₂ conditions.     

Elevated CO<Subscript>2</Subscript> influences host plant defense response in chickpea against <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

Global atmospheric concentration of CO₂ is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO₂ on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteen-day-old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO₂. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO₂ concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO₂ than in plants kept under ambient conditions. The H. armigera-infested plants had higher H₂O₂ content; amounts of oxalic and malic acids were greater at 750 ppm CO₂ than at 350 ppm CO₂. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO₂. This information will be useful for understanding effects of increased levels of CO₂ on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change.     

CO<Subscript>2</Subscript> enrichment increases element concentrations in grass mixtures by changing species abundances

Atmospheric carbon dioxide (CO₂) enrichment may increase plant growth more than the uptake of chemical elements from soil. Increased CO₂ also may alter element levels in biomass from multi-species vegetation by changing plant species abundances. We measured concentrations of ten elements in aboveground tissues of three C₄ grasses that had been exposed for 2–3 growing seasons to a continuous gradient in CO₂ from 250 to 500 μmol mol⁻¹. The grasses, Bouteloua curtipendula, Schizachyrium scoparium, and Sorghastrum nutans, are competitive dominants in assemblages of tallgrass prairie vegetation growing on each of three soil types along a field CO₂ gradient in central Texas, USA. Our objective was to determine whether CO₂ influences element concentrations in grass mixtures by changing concentrations in individual species or shifting species abundances. Increased CO₂ had little effect on element concentrations in grasses compared to differences observed among grass species and soils. Increasing CO₂ from the pre-Industrial to elevated levels reduced the phosphorus concentration in grasses grown on a clay and sandy loam soil. Concentrations of most other elements did not respond to CO₂ treatment. Cover of the mid-grass Bouteloua declined at higher CO₂ levels as cover of the taller grass Sorghastrum increased. Concentrations of several elements were lower in Bouteloua than Sorghastrum; hence, this exchange of species at higher CO₂ increased element concentrations in grass assemblages. Potential consequences include an improvement in the nutritional quality of plants for herbivores. Results highlight the underappreciated impact that CO₂ enrichment may have on ecosystem functioning by changing plant composition.     

Leaf senescence in response to elevated atmospheric CO<Subscript>2</Subscript> concentration and low nitrogen supply

This review reports the physiological and metabolic changes in plants during development under elevated atmospheric carbon dioxide concentration and/or limited-nitrogen supply in order to establish their effects on leaf senescence induction. Elevated CO₂ concentration and nitrogen supply modify gene expression, protein content and composition, various aspects of photosynthesis, sugar metabolism, nitrogen metabolism, and redox state in plants. Elevated CO₂ usually causes sugar accumulation and decreased nitrogen content in plant leaves, leading to imbalanced C/N ratio in mature leaves, which is one of the main factors behind premature senescence in leaves. Elevated CO₂ and low nitrogen decrease activities of some antioxidant enzymes and thus increase H₂O₂ production. These changes lead to oxidative stress that results in the degradation of photosynthetic pigments and eventually induce senescence. However, this accelerated leaf senescence under conditions of elevated CO₂ and limited nitrogen can mobilize nutrients to growing organs and thus ensure their functionality.     

Photosynthetic CO<Subscript>2</Subscript> uptake in seedlings of two tropical tree species exposed to oscillating elevated concentrations of CO<Subscript>2</Subscript>

Do short-term fluctuations in CO₂ concentrations at elevated CO₂ levels affect net CO₂ uptake rates of plants? When exposed to 600 μl CO₂ l^?1, net CO₂ uptake rates in shoots or leaves of seedlings of two tropical C₃ tree species, teak (Tectona grandis L. f.) and barrigon [Pseudobombax septenatum (Jacq.) Dug.], increased by 28 and 52% respectively. In the presence of oscillations with half-cycles of 20 s, amplitude of ca. 170 μl CO₂ l^?1 and mean of 600 μl CO₂ l^?1, the stimulation in net CO₂ uptake by the two species was reduced to 19 and 36%, respectively, i.e. the CO₂ stimulation in photosynthesis associated with a change in exposure from 370 to 600 μl CO₂ l^?1 was reduced by a third in both species. Similar reductions in CO₂-stimulated net CO₂ uptake were observed in T. grandis exposed to 40-s oscillations. Rates of CO₂ efflux in the dark by whole shoots of T. grandis decreased by 4.8% upon exposure of plants grown at 370 μl CO₂ l^?1 to 600 μl CO₂ l^?1. The potential implications of the observations on CO₂ oscillations and dark respiration are discussed in the context of free-air CO₂ enrichment (FACE) systems in which short-term fluctuations of CO₂ concentration are a common feature.     

RETRACTED ARTICLE: CO<Subscript>2</Subscript> effects on plant nutrient concentration depend on plant functional group and available nitrogen: a meta-analysis

Elevated CO₂ is expected to lower plant nutrient concentrations via carbohydrate dilution and increased nutrient use efficiency. Elevated CO₂ consistently lowers plant foliar nitrogen, but there is no consensus on CO₂ effects across the range of plant nutrients. We used meta-analysis to quantify elevated CO₂ effects on leaf, stem, root, and seed concentrations of B, Ca, Cu, Fe, K, Mg, Mn, P, S, and Zn among four plant functional groups and two levels of N fertilization. CO₂ effects on plant nutrient concentration depended on the nutrient, plant group, tissue, and N status. CO₂ reduced B, Cu, Fe, and Mg, but increased Mn concentration in the leaves of N₂ fixers. Elevated CO₂ increased Cu, Fe, and Zn, but lowered Mn concentration in grass leaves. Tree leaf responses were strongly related to N status: CO₂ significantly decreased Cu, Fe, Mg, and S at high N, but only Fe at low N. Elevated CO₂ decreased Mg and Zn in crop leaves grown with high N, and Mn at low N. Nutrient concentrations in crop roots were not affected by CO₂ enrichment, but CO₂ decreased Ca, K, Mg and P in tree roots. Crop seeds had lower S under elevated CO₂. We also tested the validity of a “dilution model.” CO₂ reduced the concentration of plant nutrients 6.6% across nutrients and plant groups, but the reduction is less than expected (18.4%) from carbohydrate accumulation alone. We found that elevated CO₂ impacts plant nutrient status differently among the nutrient elements, plant functional groups, and among plant tissues. Our synthesis suggests that differences between plant groups and plant organs, N status, and differences in nutrient chemistry in soils preclude a universal hypothesis strictly related to carbohydrate dilution regarding plant nutrient response to elevated CO₂.     

Experimental validation of a nonequilibrium model of CO<Subscript>2</Subscript> fluxes between gas,liquid medium,and algae in a flat-panel photobioreactor

Carbon dioxide (CO₂) availability strongly affects the productivity of algal photobioreactors, where it is dynamically exchanged between different compartments, phases, and chemical forms. To understand the underlying processes, we constructed a nonequilibrium mathematical model of CO₂ dynamics in a flat-panel algal photobioreactor. The model includes mass transfer to the algal suspension from a stream of bubbles of CO₂-enriched air and from the photobioreactor headspace. Also included are the hydration of dissolved CO₂ to bicarbonate ion (HCO₃⁻) as well as uptake and/or cycling of these two chemical forms by the cells. The model was validated in experiments using a laboratory-scale flat-panel photobioreactor that controls light, temperature, and pH and where the concentration of dissolved CO₂, and partial pressure of CO₂ in the photobioreactor exhaust are measured. First, the model prediction was compared with measured CO₂ dynamics that occurred in response to a stepwise change in the CO₂ partial pressure in the gas sparger. Furthermore, the model was used to predict CO₂ dynamics in photobioreactors with unicellular, nitrogen-fixing cyanobacterium Cyanothece sp. The metabolism changes dramatically during a day, and the distribution of CO₂ is expected to exhibit a pronounced diurnal modulation that significantly deviates from chemical equilibrium.     

Foliar quality influences tree-herbivore-parasitoid interactions: effects of elevated CO<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and plant genotype

This study examined the effects of carbon dioxide (CO₂)-, ozone (O₃)-, and genotype-mediated changes in quaking aspen (Populus tremuloides) chemistry on performance of the forest tent caterpillar (Malacosoma disstria) and its dipteran parasitoid (Compsilura concinnata) at the Aspen Free-Air CO₂ Enrichment (FACE) site. Parasitized and non-parasitized forest tent caterpillars were reared on two aspen genotypes under elevated levels of CO₂ and O₃, alone and in combination. Foliage was collected for determination of the chemical composition of leaves fed upon by forest tent caterpillars during the period of endoparasitoid larval development. Elevated CO₂ decreased nitrogen levels but had no effect on concentrations of carbon-based compounds. In contrast, elevated O₃ decreased nitrogen and phenolic glycoside levels, but increased concentrations of starch and condensed tannins. Foliar chemistry also differed between aspen genotypes. CO₂, O₃, genotype, and their interactions altered forest tent caterpillar performance, and differentially so between sexes. In general, enriched CO₂ had little effect on forest tent caterpillar performance under ambient O₃, but reduced performance (for insects on one aspen genotype) under elevated O₃. Conversely, elevated O₃ improved forest tent caterpillar performance under ambient, but not elevated, CO₂. Parasitoid larval survivorship decreased under elevated O₃, depending upon levels of CO₂ and aspen genotype. Additionally, larval performance and masses of mature female parasitoids differed between aspen genotypes. These results suggest that host-parasitoid interactions in forest systems may be altered by atmospheric conditions anticipated for the future, and that the degree of change may be influenced by plant genotype.     

Respective and interactive effects of doubled CO<Subscript>2</Subscript> and O<Subscript>3</Subscript> concentration on membrane lipid peroxidation and antioxidative ability of soybean

Effects of doubled CO₂ and O₃ concentration on Soybean were studied in open-top chambers (OTC). Under doubled CO₂ concentration, grain yield and biomass increased, the SOD activity, vitamin C (Vc) and carotenoid (Car) content also increased; Superoxide (O₂ ^?) generating rate decreased, relative conductivity and malondialdehyde (MDA) content significantly declined. But under doubled O₃ concentration, the SOD activity, Vc and Car contents declined, resulting in imbalance of activated-oxygen production, enhanced O₂ ^? generating rate and accelerated process of lipid peroxidation and increase in MDA content and ion leakage of leaves. The final result was decreased grain yield and plant biomass. Interactive effects of doubled CO₂ and O₃ concentrations on soybean were mostly counteractive. However, the beneficial effects of concentration-doubled CO₂ are more than compensate the negative effects imposed by doubled O₃, and the latter in its turn partly counteracted the positive effects of the former.     

Effects of elevated CO<Subscript>2</Subscript> applied to potato roots on the anatomy and ultrastructure of leaves

The root system of potato (Solanum tuberosum L. cv. Favorita) plants was treated with different O₂ and CO₂ concentrations for 35 d in aeroponic culture. Under 21 or 5 % O₂ in the root zones, the thickness of leaves and palisade parenchyma significantly increased at 3 600 μmol(CO₂) mol⁻¹ in the root zone, compared with CO₂ concentration 380 μmol mol⁻¹ or low CO₂ concentration (100 μmol mol⁻¹). In addition, smaller cells of palisade tissue, more intercellular air spaces and partially two layers of palisade cells were observed in the leaves with root-zone CO₂ enrichment. Furthermore, there was a significant increase in the size of chloroplasts and starch grains, and the number of starch grains per chloroplast due to elevated CO₂ only under 21 % O₂. In addition, a significant decline in the thickness of grana and the number of lamellas, but no significant differences in the number of grana per chloroplast were observed under elevated CO₂ concentration. The accumulation of starch grains in the chloroplast under elevated CO₂ concentration could change the arrangement of grana thylakoids and consequently inhibited the absorption of sun radiation and photosynthesis of potato plants.     

Down-regulation of Rubisco activity under combined increases of CO<Subscript>2</Subscript> and temperature minimized by changes in Rubisco k<Subscript>cat</Subscript> in wheat

Increases in growth temperature have been observed to affect photosynthesis differently under long-term exposure to ambient- and twice ambient-air CO₂ concentrations. This study investigates the causes of this interaction in wheat (Triticum aestivum L.) grown in the field over two consecutive years under temperature gradient chambers in ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂ concentrations and at ambient or ambient +4°C temperatures, with either a low or a high nitrogen supply. The photosynthesis-internal CO₂ response curves and the activity, activation state, k_cat and amount of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were measured, as well as the soluble protein concentration in flag leaves at ear emergence and 8–15 days after anthesis. A high nitrogen supply increased V_cmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco k_cat. Both elevated CO₂ and above ambient temperatures had negative effects on V_cmax and Rubisco activity, but at elevated CO₂, an increase in temperature did not decrease V_cmax or Rubisco activity in relation to ambient temperature. The amounts of Rubisco and soluble protein decreased with elevated CO₂ and temperature. The negative impact of elevated CO₂ on Rubisco properties was somewhat counteracted at elevated temperatures by an increase in k_cat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO₂ and temperature.     

The stomatal CO<Subscript>2</Subscript> proxy does not saturate at high atmospheric CO<Subscript>2</Subscript> concentrations: evidence from stomatal index responses of Araucariaceae conifers

The inverse relationship between the number of stomata on a leaf surface and the atmospheric carbon dioxide concentration ([CO₂]) in which the leaf developed allows plants to optimise water-use efficiency (WUE), but it also permits the use of fossil plants as proxies of palaeoatmospheric [CO₂]. The ancient conifer family Araucariaceae is often represented in fossil floras and may act as a suitable proxy of palaeo-[CO₂], yet little is known regarding the stomatal index (SI) responses of extant Araucariaceae to [CO₂]. Four Araucaria species (Araucaria columnaris, A. heterophylla, A. angustifolia and A. bidwillii) and Agathis australis displayed no significant relationship in SI to [CO₂] below current ambient levels (~380 ppm). However, representatives of the three extant genera within the Araucariaceae (A. bidwillii, A. australis and Wollemia nobilis) all exhibited significant reductions in SI when grown in atmospheres of elevated [CO₂] (1,500 ppm). Stomatal conductance was reduced and WUE increased when grown under elevated [CO₂]. Stomatal pore length did not increase alongside reduced stomatal density (SD) and SI in the three araucariacean conifers when grown at elevated [CO₂]. These pronounced SD and SI reductions occur at higher [CO₂] levels than in other species with more recent evolutionary origins, and may reflect an evolutionary legacy of the Araucariaceae in the high [CO₂] world of the Mesozoic Era. Araucariacean conifers may therefore be suitable stomatal proxies of palaeo-[CO₂] during periods of “greenhouse” climates and high [CO₂] in the Earth’s history.     

Mass Spectrometric Analysis of the Antinociceptive Effect of Lidocaine

Relative measurements of the concentration of CO₂ released through the skin in rats in response to thermal stimulation were performed using a mass spectrometer with a membrane interface. It is demonstrated that the antinociceptive response to a pain stimulus during intraperitoneal propofol–lidocaine and propofol–ketamine anesthesia can be monitored using a mass spectrometer with a membrane interface. Lidocaine exerts direct action on the central nervous system and induces an antinociceptive effect in response to thermal stimulation.