Responses of stomata of senescing and nonsenescing leaves of Nicotians glauca to changes in intercellular concentrations of leaf carbon dioxide

Abstract. Gas exchange measurements were performed to test the hypothesis that failure of stomata to open in senescing leaves of Nicotiana glauca is caused by elevated concentrations of carbon dioxide in the intercellular spaces of leaf mesophyll tissue (c_i). Senescing leaves selected for experiments were completely chlorotic and lacked positive rates of photosynthesis. When stomata in detached epidermis from senescing leaves were illuminated in CO2-free air, they opened to similar apertures as those in detached epidermis from nonsenescing leaves. To compare the effects of changes in c_i on stomatal responses of the two leaf types, leaf 'flags' of either nonsenescing or senescing leaves were illuminated at a photosynthetic photon flux density of 500 μmol m⁻² s⁻¹ in a gas exchange cuvette. Leaf temperatures were maintained at 23.5 ± 0.5°C, and vapour pressure differences between leaves and the air were maintained between 0.70 and 0.75kPa. C_i was adjusted by changing external concentrations of carbon dioxide in air circulating through the cuvette. Conductances and photosynthetic rates of nonsenescing leaves changed in response to changes in c_i, but neither the conductances nor the photosynthetic rates of senescing leaves were affected significantly by changes in q. We conclude that guard cells of senescing leaves of Nicotiana glauca do not lose the capacity to respond to changes in carbon dioxide concentration and that increases in c_i resulting from declining rates of mesophyll photosynthesis are not the sole cause of maintenance of stomatal closure during leaf senescence. The data suggest that factors external to guard cells may prevent them from responding to changes in carbon dioxide concentrations in intact senescing leaves.     

Effect of elevated CO2 on the stomatal distribution and leaf physiology of Alnus glutinosa

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 μmol mol⁻¹ CO₂) and double ambient (720 μmol mol⁻¹ CO₂) carbon dioxide (CO₂) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO₂ concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO₂ concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO₂ concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation ( V _cmax) and the light saturated rate of electron transport ( J _max) between the control and elevated CO₂ treatment.     

Effects of boundary layer conductance on substomatal pressures of carbon dioxide

Abstract. Gas exchange measurements were made on single leaves of three C₃ and one C₄ species at air speeds of 0.4 and 4.0 m s⁻¹ to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m⁻² s⁻¹ at the lower air speed, and 1.2 to 1.5 mol m⁻² s⁻¹ at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C₃ species, and about 3 Pa lower in the C₄ species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C₃ species. The commonly reported values of substomatal carbon dioxide pressure for C₃ and C₄ species were found to occur only when measurements were made at the higher air speed.     

Relationship of environmental pCO2 to selected blood parameters of Oncorhynchus kisutch (Walbaum)

Blood samples from sub-adult coho salmon ( Oncorhynchus kisutch ) were correlated with environmental conditions. Carbon dioxide tensions, pH and bicarbonate levels were determined in the blood for fish acclimated to environmental pCO₂ levels of 2.49 and 2.74 mmHg. Fish were removed from the high pCO₂ environment and placed in one with a low pCO₂. Their blood pH and pCO₂ were monitored during the course of acclimation. After 27 days of acclimation to a low pCO₂ environment, a group of fish was sampled and compared to a group of fish acclimated to a high pCO₂ environment. It was found that pCO₂ in the environment affects the rate of diffusion of carbon dioxide from the blood to the water. Under the environmental conditions prescribed in these experiments no significant change in bicarbonate was noticed. It is postulated that a bicarbonate chloride exchange is not a major pathway for the removal of carbon dioxide from the blood of O. kisutch .     

Variation in growth stimulation by elevated carbon dioxide in seedlings of some C3 crop and weed species

Seven C₃ crop and three C₃ weed species were grown from seed at 360 and at 700 cm³ m^–3 carbon dioxide concentrations in a controlled environment chamber to compare dry mass, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and photosynthetic acclimation at ambient and elevated carbon dioxide. The dry mass at the final harvest at elevated carbon dioxide relative to that at ambient carbon dioxide was highly correlated with the RGR at the lower carbon dioxide concentration. This relationship could be quite common, because it does not require that species differ in the response of RGR or photosynthesis to elevated carbon dioxide, and holds even when species differ moderately in these responses. RGR was also measured for a limited period at the end of the experiment to determine relationships with leaf gas exchange measured at this time. Relative increases in RGR at elevated carbon dioxide at this time were more highly correlated with the relative increase in NAR at elevated carbon dioxide than with the response of LAR. The amount of acclimation of photosynthesis was a good predictor of the relative increase in NAR at elevated carbon dioxide, and the long-term increase in photosynthesis in the growth environment. No differences between crops and weeds or between cool and warm climate species were found in the responses of growth or photosynthetic acclimation to elevated carbon dioxide.     

Determination of dissolved carbon dioxide by coulometric titration in modified atmosphere systems

The solubility of carbon dioxide (CO₂) in microbiological media at different pH values, water activities ( a_w ), temperatures, buffering capacities and ratios of headspace to media volumes was determined by using a coulometer. Buffering capacity and ratio of headspace to media volume were shown to be the major factors influencing the solubility of CO₂ in modified atmosphere model systems. The growth inhibitory effects of different dissolved CO₂ concentrations (0–50 μmol ml^-1) were determined for Pseudomonas fragi at 8°C and 22 C. Pseudomonas fragi was shown to be strongly affected by the CO₂ concentration in the media. A carbon dioxide concentration of 40 μmol ml^-1 was needed to inhibit Ps. fragi at 8°C. The importance of measuring dissolved CO₂ concentrations in modified atmosphere packaging applications was shown and the coulometer proved to be an excellent tool for this purpose.     

Assimilation of methane and inorganic carbon by microbial communities mediating the anaerobic oxidation of methane

The anaerobic oxidation of methane (AOM) is a major sink for methane on Earth and is performed by consortia of methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). Here we present a comparative study using in vitro stable isotope probing to examine methane and carbon dioxide assimilation into microbial biomass. Three sediment types comprising different methane-oxidizing communities (ANME-1 and -2 mixture from the Black Sea, ANME-2a from Hydrate Ridge and ANME-2c from the Gullfaks oil field) were incubated in replicate flow-through systems with methane-enriched anaerobic seawater medium for 5–6 months amended with either ¹³CH₄ or H¹³CO₃^-. In all three sediment types methane was anaerobically oxidized in a 1:1 stoichiometric ratio compared with sulfate reduction. Similar amounts of ¹³CH₄ or ¹³CO₂ were assimilated into characteristic archaeal lipids, indicating a direct assimilation of both carbon sources into ANME biomass. Specific bacterial fatty acids assigned to the partner SRB were almost exclusively labelled by ¹³CO₂, but only in the presence of methane as energy source and not during control incubations without methane. This indicates an autotrophic growth of the ANME-associated SRB and supports previous hypotheses of an electron shuttle between the consortium partners. Carbon assimilation efficiencies of the methanotrophic consortia were low, with only 0.25–1.3 mol% of the methane oxidized.     

Physiological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strain

Abstract. The metabolic rates, as expressed by oxygen (O₂) consumption, carbon dioxide (CO₂) production, and losses in wet and dry weights, were examined for adults of three strains of the red flour beetle Tribolium castaneum (Herbst), during exposure to two modified atmospheres (MAs). Exposure of a strain selected for resistance over twenty-one generations to an atmosphere of 65% CO₂, 20% O₂ and the balance nitrogen (N₂), termed a high carbon dioxide concentration atmosphere (HCC) and exposure of an unselected strain to HCC, showed considerable levels of aerobic metabolism during exposure. For the unselected strain water loss and mobilization of energy reserves were rapid and mortality was followed by rapid desiccation. For the HCC-resistant strain water balance was maintained and energy reserves were utilized more slowly over a prolonged period. Exposure of a strain selected for resistance over twenty-one generations to a low oxygen concentration atmosphere (LOC) of 0.5% O₂ in N₂, and an unselected strain to LOC, revealed that even at 0.5% O₂, metabolism was largely aerobic in both strains. Maintenance of water balance was not a major factor causing mortality of either strain during exposure to LOC. In air, metabolic rates of both the resistant strains were lower than that of the unselected strain.     

Productivity and community structure of ectomycorrhizal fungal sporocarps under increased atmospheric CO2 and O3

Sporocarp production is essential for ectomycorrhizal fungal recombination and dispersal, which influences fungal community dynamics. Increasing atmospheric carbon dioxide (CO₂) and ozone (O₃) affect host plant carbon gain and allocation, which may in turn influence ectomycorrhizal sporocarp production if the carbon available to the ectomycorrhizal fungus is dependant upon the quantity of carbon assimilated by the host. We measured sporocarp production of ectomycorrhizal fungi over 4 years at the Aspen FACE (free air CO₂ enrichment) site, which corresponded to stand ages seven to 10 years. Total mean sporocarp biomass was greatest under elevated CO₂, regardless of O₃ concentration, while it was generally lowest under elevated O₃ with ambient CO₂. Community composition differed significantly among the treatments, with less difference in the final year of the study. Whether this convergence was due to succession or environmental factors is uncertain. CO₂ and O₃ affect ectomycorrhizal sporocarp productivity and community composition, with likely effects on dispersal, colonization and sporocarp-dependent food webs.     

Photoinhibition of respiratory CO2 release in the green alga Scenedesmus

¹⁴CO₂ evolution of prelabeled Scenedesmus obliquus Kütz, has been followed in the dark and in the light. In the light, no carbon dioxide is evolved. Addition of unlabeled NaHCO, leads to ¹⁴CO₂ release attaining 20 to 30% of the dark rate. Double-reciprocal plots of NaHCO₃ concentrations vs ¹⁴CO₂ release results in a straight line, indicative of competition between exogenously supplied bicarbonate and endogenously evolved carbon dioxide. With this method, it is possible to measure CO₂ evolved by respiration in the light and to show that true photoinhibition of respiration occurs in Scenedesmus . In the light. DCMU substantially increases ¹⁴CO₂ evolution; in the presence of the uncoupler carbonyl cyanide- m -chlorophenylhydrazone. ¹⁴CO₂ evolution is comparable to that in the dark. ¹⁴CO₂ release and oxygen uptake in the dark are only slightly affected by cyanide, indicative of a cyanide-resistant respiration and/or fermentation as the essential CO₂-yielding processes in the presence of cyanide. These results, compared with concurrent ATP levels, lead us to assume that energy charge is not the only factor responsible for photoinhibition of respiration.     

Photosynthesis and photoassimilation of glucose during photomixotrophic growth of Marchantia polymorpha cells in suspension culture

Even in the presence of glucose the growth of Marchantia polymorpha L. (cell line HYH-2F) requires light, and growth is more sensitive to 10⁻⁶ M 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea than to 10⁻⁴ Antimycin A. The inability of the cells to grow in the dark is due to the low level of respiration. The respiration rate under light increased to four times the dark value. The values of the compensation ratio (the photosyntehtic rate/the respiration rate) for the oxygen exchange were below 1.0 daring the growth period, although oxygen evolution was found. At the early exponential phase, oxygen evolution was 0.373 μmol (mg cell dry weight)⁻¹ h⁻¹ [61.7 μmol (mg chlorophyll)⁻¹ h⁻¹]. M. polymorpha cells are unable to grow anaerobically in the light without a supply of carbon dioxide. When 1% carbon dioxide in nitrogen is supplied, photochemically produced oxygen and energy are sufficient for sustained growth although at significantly reduced yields in both cell dry weight and chlorophyll. Photosyntehtic CO₂ assimilation rate was 0.13 μmol (mg cell dry weight)⁻¹ h⁻¹[11.3 μmol (mg chlorophyll)⁻¹ h⁻¹]. At least one-third of the carbon atoms in cellular constituents seem to be derived from atmospheric carbon dioxide, which indicates that M. polymorpha cells grow photomixotrophicaily.     

Elevated concentrations of atmospheric CO2 protect against and compensate for O3 damage to photosynthetic tissues of field-grown wheat

The effects of elevated concentrations of atmospheric carbon dioxide and ozone on diurnal patterns of photosynthesis have been investigated in field-grown spring wheat ( Triticum aestivum ). Plants cultivated under realistic agronomic conditions, in open-top chambers, were exposed from emergence to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at ambient (380 μmol mol⁻¹, seasonal mean) or elevated (692 μmol mol⁻¹) levels, [O₃] at ambient (27 nmol mol⁻¹, 7 hr seasonal mean) or elevated (61 nmol mol⁻¹) levels. After anthesis, diurnal measurements were made of flag-leaf gas-exchange and in vitro Rubisco activity and content. Elevated [CO₂] resulted in an increase in photoassimilation rate and a loss of excess Rubisco activity. Elevated [O₃] caused a loss of Rubisco and a decline in photoassimilation rate late in flag-leaf development. Elevated [CO₂] ameliorated O₃ damage. The mechanisms of amelioration included a protective stomatal restriction of O₃ flux to the mesophyll, and a compensatory effect of increased substrate on photoassimilation and photosynthetic control. However, the degree of protection and compensation appeared to be affected by the natural seasonal and diurnal variations in light, temperature and water status.     

Effects of cucumber mosaic virus infection on electron transport and antioxidant system in chloroplasts and mitochondria of cucumber and tomato leaves

We examined the responses of the photosynthetic and respiratory electron transport and antioxidant systems in cell organelles of cucumber ( Cucumis sativus L.) and tomato ( Lycopersicon esculentum Mill.) leaves to infection of cucumber mosaic virus (CMV) by comparing the gas exchange, Chl fluorescence, respiratory electron transport, superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate–glutathione (AsA–GSH) cycle enzymes and the production of H₂O₂ in chloroplasts, mitochondria and soluble fraction in virus-infected and non-infected leaves. Long-term CMV infection resulted in decreased photosynthesis and respiration rates. Photosynthetic electron flux to carbon reduction, respiratory electron transport via both complex I and complex II and also the Cyt respiration rate all significantly decreased, while photosynthetic alternative electron flux and alternative respiration significantly increased. These changes in electron transport were accompanied by a general increase in the activities of SOD/AsA–GSH cycle enzymes followed by an increased H₂O₂ accumulation in chloroplasts and mitochondria. These results demonstrated that disturbance of photosynthetic and respiratory electron transport by CMV also affected the antioxidative systems, thereby leading to oxidative stress in various organelles.     

The comparative effects of nitrogen and oxygen on the microflora of beef steaks in carbon dioxide-containing modified atmosphere vacuum skin-packaging (MA-VSP) systems

The effects of 80% oxygen–20% carbon dioxide (O₂–CO₂) and 80% nitrogen–20% carbon dioxide (N₂–CO₂) atmospheres were compared with respect to the microbial and sensory characteristics of vacuum skin-packaged grain-fed beef steaks stored at −1 and 4 °C. In both N₂–CO₂ and O₂–CO₂ atmospheres, lactobacilli were predominant over Brochothrix , pseudomonads, enterobacteria and yeasts and moulds. The results of the current investigation showed that the O₂–CO₂ atmospheres did not yield total viable counts in excess of 10⁵ cfu cm⁻² on beef steaks after 4 weeks of storage. However, the sensory analysis and thiobarbituric acid (TBA) values (as a measure of oxidative rancidity) of the products were unacceptable at this time. In contrast, the N₂–CO₂ atmospheres yielded maximum total viable counts of approximately 10⁷ cfu cm⁻² and the sensory analysis and TBA values of the product were judged to be acceptable after 4 weeks of storage at −1 °C. These results indicate that sensory effects of the product were influenced to a greater extent by the chemical effects of high concentration of O₂ on rancidity than by the high levels of lactobacilli.     

On the participation of chloride in bicarbonate-induced reversal of anion inhibition of photosystem II electron transport in spinach thylakoids

Inhibition of electron transport through photosystem II (PS II) by formate (HCO⁻₂) or nitrite (NO⁻₂) in the presence or absence of chloride ions was studied. The inhibition induced by HCO⁻₂ or NO⁻₂ is overcome by HCO⁻₃ more in the presence, than in the absence of Cl⁻. The data on electron transport are supported by chlorophyll a fluorescence measurements. In experiments. In experiments in which water oxidation was blocked. Cl⁻ was found to facilitate electron transport between bound quinone A (Q⁻_A) and the plastoquinone (PQ) pool. It can thus be concluded that in addition to the well known site of action of Cl⁻ on water oxidation, another site of Cl⁻ action is between Q⁻_A and the PQ pool.     

Estimation of parameters of a biochemically based model of photosynthesis using a genetic algorithm

Photosynthesis response to carbon dioxide concentration can provide data on a number of important parameters related to leaf physiology. The genetic algorithm (GA), which is a robust stochastic evolutionary computational algorithm inspired by both natural selection and natural genetics, is proposed to simultaneously estimate the parameters [including maximum carboxylation rate allowed by ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate ( V _cmax), potential light-saturated electron transport rate ( J _max), triose-phosphate utilization (TPU), leaf dark respiration in the light ( R _d) and mesophyll conductance ( g _m)] of the photosynthesis models presented by Farquhar, von Caemmerer and Berry, and Ethier and Livingston. The results show that by properly constraining the parameter bounds the GA-based estimate methods can effectively and efficiently obtain globally (or, at least near globally) optimal solutions, which are as good as or better than those obtained by non-linear curve fitting methods used in previous studies. More complicated problems such as taking the g _m variation response to CO₂ into account can be easily formulated and solved by using GA. The influence of the crossover probability ( P _c), mutation probability ( P _m), population size and generation on the performance of GA was also investigated.     

Expression of Bradyrhizobium japonicum cbb3 terminal oxidase under denitrifying conditions is subjected to redox control

Bradyrhizobium japonicum utilizes cytochrome cbb ₃ oxidase encoded by the fixNOQP operon to support microaerobic respiration under free-living and symbiotic conditions. It has been previously shown that, under denitrifying conditions, inactivation of the cycA gene encoding cytochrome c ₅₅₀, the electron donor to the Cu-containing nitrite reductase, reduces cbb ₃ expression. In order to establish the role of c ₅₅₀ in electron transport to the cbb ₃ oxidase, in this work, we have analyzed cbb ₃ expression and activity in the cycA mutant grown under microaerobic or denitrifying conditions. Under denitrifying conditions, mutation of cycA had a negative effect on cytochrome c oxidase activity, heme c (FixP and FixO) and heme b cytochromes as well as expression of a fixP '–' lacZ fusion. Similarly, cbb ₃ oxidase was expressed very weakly in a napC mutant lacking the c -type cytochrome, which transfers electrons to the NapAB structural subunit of the periplasmic nitrate reductase. These results suggest that a change in the electron flow through the denitrification pathway may affect the cellular redox state, leading to alterations in cbb ₃ expression. In fact, levels of fixP '–' lacZ expression were largely dependent on the oxidized or reduced nature of the carbon source in the medium. Maximal expression observed in cells grown under denitrifying conditions with an oxidized carbon source required the regulatory protein RegR.     

Protonmotive force-driven synthesis of ATP during methane formation from molecular hydrogen and formaldehyde or carbon dioxide in Methanosarcina barkeri

Abstract Methane formation from formaldehyde and H₂ or from carbon dioxide and H₂, as performed by cell suspensions of Methanosarcina barkeri , was coupled to ATP synthesis. In correspondence with this, methane formation was inhibited by N , N '-dicyclohexylcarbodiimide (DCCD), which at the same time, caused a decrease of the intracellular ATP concentration but only a slow decrease of the membrane potential. Addition of the uncoupler tetrachlorosalicylanilide (TCS) led to a relief of the inhibition of methane formation from CH₂O + H₂, but not from CO₂+ H₂.     

Species-specific responses to atmospheric carbon dioxide and tropospheric ozone mediate changes in soil carbon

We repeatedly sampled the surface mineral soil (0–20 cm depth) in three northern temperate forest communities over an 11-year experimental fumigation to understand the effects of elevated carbon dioxide (CO₂) and/or elevated phyto-toxic ozone (O₃) on soil carbon (C). After 11 years, there was no significant main effect of CO₂ or O₃ on soil C. However, within the community containing only aspen ( Populus tremuloides Michx.), elevated CO₂ caused a significant decrease in soil C content. Together with the observations of increased litter inputs, this result strongly suggests accelerated decomposition under elevated CO_2. In addition, an initial reduction in the formation of new (fumigation-derived) soil C by O₃ under elevated CO₂ proved to be only a temporary effect, mirroring trends in fine root biomass. Our results contradict predictions of increased soil C under elevated CO₂ and decreased soil C under elevated O₃ and should be considered in models simulating the effects of Earth's altered atmosphere.     

Relationship between photosystem II activity and CO2 fixation in leaves

There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO₂ fixed. A measure of the quantum yield of photosystem II, Φ_II (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals Φ_II times incident light intensity times the fraction of incident light absorbed by PSII. In C₄ plants, there is a linear relationship between PSII activity and CO₂ fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C₄ species. In C₃ plants, both CO₂ fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO₂, or per O₂ reacting with RuBP). The rates of PSII activity associated with photosynthesis in C₃ plants, based on estimates of the rates of carboxylation (v_o) and oxygenation (v_o) at various levels of CO₂ and O₂, largely account for the PSII activity determined from fluorescence measurements. Thus, in C₃ plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO₂ fixation.