Autotrophic CO2 fixation in Chlorobium limicola. Evidence against the operation of the Calvin cycle in growing cells

Chlorobium limicola has been proposed to assimilate CO₂ autotrophically via a reductive tricarboxylic acid cycle rather than via the Calvin cycle. This proposal has been a matter of considerable controversy. In order to determine which pathway is operative, the bacterium was grown on a mineral salts medium with CO₂ as the main carbon source supplemented with specifically labeled ¹⁴C-pyruvate, and the incorporation of ¹⁴C into alanine (intracellular pyruvate), aspartate (oxaloacetate), glutamate (-ketoglutarate), and glucose (hexosephosphate) was measured in exponentially growing cells in long term labeling experiments. During growth in presence of pyruvate, 20% of the cell carbon were derived from pyruvate in the medium, 80% from CO₂. Since pyruvate was not oxidized to CO₂, only those compounds should become labeled which were synthesized from CO₂ via pyruvate.The three amino acids and glucose were found to be labeled. Alanine had one fifth the specific radioactivity of the extracellular pyruvate, indicating that 20% of the intracellular pyruvate pool were derived from pyruvate in the medium, 80% were synthesized from CO₂. Glucose had twice the specific radioactivity of alanine, showing that hexosephosphate synthesis from CO₂ proceeded via the pyruvate pool. The latter finding is not consistent with the operation of the Calvin cycle, in which pyruvate is not an intermediate. The specific radioactivities of aspartate (oxaloacetate) and of glutamate (-ketoglutarate) were practically identical but considerably lower than that of alanine ( intracellular pyruvate). These findings are compatible with the operation of a reductive tricarboxylic acid cycle as mechanism of autotrophic CO₂ fixation. Degradation studies of the cell components support this interpretation. Offprint requests to: G. Fuchs     

Short-term CO2 exchange response to temperature,irradiance, and CO2 concentration in strawberry

Relative importance of short-term environmental interaction and preconditioning to CO₂ exchange response was examined in Fragaria ananasa (strawberry, cv. Quinault). Tests included an orthogonal comparison of 15 to 60-min and 6 to 7-h exposures to different levels of temperature (16 to 32°C), photosynthetically active radiation (PAR, 200 to 800 E m² s^-1), and CO₂ (300 to 600 l/l) on successive days of study. Plants were otherwise maintained at 21°C, 300 E m² s^-1 PAR and 300–360 l/l CO₂ as standard conditions. Treatment was restricted to the mean interval of 14 h daily illumination and the first 3–4 days of each test week over a 12-week cultivation period. CO₂ exchange rates were followed with each step-change in environmental level including ascending/descending temperature/PAR within a test period, initial response at standard conditions on successive days of testing, and measurement at reduced O₂. Response generally supported prior concepts of leaf biochemical modeling in identifying CO₂ fixation as the major site of environmental influence, while overall patterns of whole plant CO₂ exchange suggested additional effects for combined environmental factors and preconditioning. These included a positive interaction between temperature and CO₂ concentration on photosynthesis at high irradiance and a greater contribution by dark respiration at lower PAR than previously indicated. The further importance of estimating whole plant CO₂ exchange from repetitive tests and measurements was evidenced by a high correlation of response to prior treatment both during the daily test period and on consecutive days of testing.Abbreviations C₃ plant a plant in which the product of CO₂ fixation is a 3-carbon acid (3-phosphoglyceric acid) - IRGA intra-red gas analyzer - PAR photosynthetically active radiation - RH relative humidity - RuBisCO ribulose-1,5-bisphosphate carboxylase/oxygenase Reference to a company and/or product named by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.     

Leaf cavity CO2 concentrations and CO2 exchange in onion,Allium cepa L.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO₂ that accumulates within their leaf cavities. Leaf cavity CO₂ concentrations ranged from 2250 L L^–1 near the leaf base to below atmospheric (<350 L L^–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO₂ concentrations with minimum values near midday and maximum values at night. Conductance to CO₂ from the leaf cavity ranged from 24 to 202 mol m^–2 s^–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO₂ was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO₂ concentrations and conductance values or as measured directly by ¹⁴CO₂ labeling experiments. The photosynthetic responses to CO₂ and O₂ were measured to determine whether onion leaves exhibited a typical C₃-type response. A linear increase in CO₂ uptake was observed in intact leaves up to 315 L L^–1 of external CO₂ and, at this external CO₂ concentration, uptake was inhibited 35.4±0.9% by 210 mL L^–1 O₂ compared to 20 mL L^–1 O₂. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO₂ and greatly restrict the refixation of leaf cavity CO₂ by photosynthetic tissue.Abbreviations C_a external CO₂ concentration - C_i intercellular CO₂ concentration - CO₂ compensation concentration - PPFR photosynthetic photon fluence rate     

Structural and Functional Features of the Escherichia coli F 1 -ATPase

The structural organization and overall dimensions of the Escherichia coli F₁-ATPase in solutionhas been analyzed by synchroton X-ray scattering. Using an independent ab initio approach,the low-resolution shape of the hydrated enzyme was determined at 3.2 nm resolution. Theshape permitted unequivocal identification of the volume occupied by the _{3 3} complex ofthe atomic model of the ECF₁-ATPase. The position of the ^ and subunits were found byinteractive fitting of the solution scattering data and by cross-linking studies. Laser-inducedcovalent incorporation of 2-azido-ATP established a direct relationship between nucleotidebinding affinity and the different interactions between the stalk subunits and with the threecatalytic subunits () of the F₁-ATPase. Mutants of the ECF₁-ATPase with the introductionof Trp-for-Tyr replacement in the catalytic site of the complex made it possible to monitorthe activated state for ATP synthesis (ATP conformation) in which the and subunits arein close proximity to the subunits and the ADP conformation, with the stalk subunits arelinked to the subunit.     

Effect of CO2 enrichment and nitrogen availability on resource acquisition and resource allocation in a grass,Bromus mollis

Summary The effects of CO₂ enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C₃), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO₂ enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 l/l for the CO₂-enriched plants, compared to photosynthetic rates measured at 350 l/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 l/l were greater than photosynthetic rates of the non-enriched plants measured at 350 l/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO₂ enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO₂ treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO₂ tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen.     

Competition between electron acceptors in photosynthesis: Regulation of the malate valve during CO2 fixation and nitrite reduction

For maximal rates of CO₂ assimilation in isolated intact spinach chloroplasts the generation of the adequate NADPH/ATP ratio is achieved either by cyclic electron flow around photosystem I or by linear electron transport to oxaloacetate, nitrite or oxygen (Mehler-reaction). The interrelationships between these poising mechanisms turn out to be strictly hierarchical. In the presence of antimycin A, an inhibitor of ferredoxin-dependent cyclic electron transport, the reduction of both, oxaloacetate and nitrite, but not that of oxygen restores CO₂ fixation. When oxaloacetate and nitrite are added at low concentrations simultaneously during steady-state CO₂ fixation, the reduction of nitrite is clearly preferred over the reduction of oxaloacetate, but CO₂ fixation is not influenced. Nitrite reduction is not decreased upon addition of oxaloacetate, but vice versa. This is due to the regulation of NADP-malate dehydrogenase activation by electron pressure via the ferredoxin/thioredoxin system on the one hand, and by the NADPH/(NADP+NADPH) ratio (anabolic reduction charge, ARC) on the other hand. Thus the closing of the malate valve prevents drainage of reducing equivalents from the chloroplast (1) when a low ARC indicates a high demand for NADPH in the stroma and (2) when nitrite reduction reduces the electron pressure at ferredoxin. The malate valve is opened when cyclic electron transport is inhibited by antimycin A. Under these conditions the rate of malate formation is higher than in the absence of the inhibitor even in the presence of oxaloacetate, thus indicating that the regulation of the malate valve functions at various redox states of the acceptor side of Photosystem I.Abbreviations ARC anabolic reduction charge (NADPH/(NADP+NADPH)) - Chl chlorophyll - DTT dithiothreitol; Fd-ferredoxin - NADP-MDH NADP-malate dehydrogenase - OAA oxaloacetate - PS photosystem - qN non-photochemical quenching - qP photochemical quenching - _E quantum efficiency of PS II Dedicated to Prof. Dr. Hans Walter Heldt on the occasion of his 60th birthday.     

Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves

Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO₂ assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO₂ assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO₂ assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C₃ leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO₂ assimilation.Abbreviations Fm, Fo, Fv maximal, minimal and variable fluorescence yields - Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_P photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - _{PS I}, _{PS II} relative quantum efficiencies of PS I and PS II photochemistry - _{CO 2} quantum yield of CO₂ assimilation     

The electrochemical H+ gradient in the yeastRhodotorula glutinis

The electrochemical gradient of protons, , was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH₀ range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP⁺) for negative above pH₀ 4.5, and thiocyanate (SCN^–) for positive below pH₀ 4.5. The chemical gradient of H⁺ was determined by measuring the chemical shift of intracellular P_i by³¹P-NMR at given pH₀ values. The values of pH_i increased almost linearly from 7.3 at pH₀ 3 to 7.8 at pH₀ 8.5. In the physiological pH₀ range from 3.5 to 6, was fairly constant at values between 17–18 KJ mol^–1, gradually decreasing at pH₀ above 6. In deenergized cells, the intracellular pH_i decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH₀ 4.5 or 7.5. There was no membrane potential detectable in deenergized cells.     

The carbon isotope ratio of plant organic material reflects temporal and spatial variations in CO2 within tropical forest formations in Trinidad

Summary A method of monitoring and collecting CO₂ samples in the field has been developed which has been used to study both temporal and spatial variations in canopy CO₂ isotopic signatures in two contrasting tropical forest formations in Trinidad. These have been related to vertical gradients in the carbon isotope ratio (¹³C) of organic material in conjunction with measurements of other environmental parameters. The ¹³C of leaf material from two canopies showed a gradient with respect to height, more negative values being found low in the understorey. The deciduous secondary forest, (Simla) showed a difference of 4.6 and the semi-evergreen seasonal canopy (Aripo), 2.8. The range of ¹³C values at Simla was 4 less negative than those at Aripo. In order to relate these measurements to the interaction between diffusion or carboxylation limitation, and source CO₂ effects, variations in environmental parameters through the canopy have been compared with changes in CO₂ partial pressure (P _a) and isotopic composition ¹³C throughout the day during the dry season. Values of P _a20 m above the ground at Aripo varied from 380 vpm at dawn to 340 vpm at midday, at which time the partial pressure 15 cm above the ground was 375 vpm. The CO₂ partial pressure did not stabilise during the course of the day, and there was good correlation (r ²=0.82) between _a and P _a, with more negative values of _a occuring in the understorey. Diuraal changes of 2 were evident at all canopy positions. In the more open canopy at Simla, these gradients were similar, but less marked. Leaf-air vapour pressure deficit (VPD) showed no relationship with height, possibly as a result of minimal water flux from both the soil and the canopy due to low soil water content; VPD was 1.5 kPa higher at midday than dawn. A 3° C temperature gradient between the understorey and upper canopy was observed at Aripo but not in the more open Simla canopy. CO₂ partial pressure stabilised for only 4 h in the middle of the day, while other parameters showed no stable period. The proportion of floor respired CO₂ reassimilated at Aripo has been calculated as 26%, 19%, and 8% for the periods 0600–1000, 1000–1400, and 1400–1800 hours. In order to quantify source CO₂ effects, measurements of the environmental parameters and assimilation rate must be made at all canopy positions and throughout the day.     

Elevated CO2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an Endoaquept soil

Effects of elevated CO₂ (700 L L^–1) and a control (350 L L^–1 CO₂) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 L L^–1 CO₂ and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the 700 L L^–1 CO₂ treatment were ca. 7% greater than in the control at the end of the summer period. Root mass (to ca 25 cm depth) in the 700 L L^–1 CO₂ treatment was then about 50% greater than in the control, but in the 700 L L^–1 CO₂+6°C treatment it was 6% lower than in the control. Based on decomposition results, herbage from the 700 L L^–1+6°C treatment probably contained the highest proportion of readily decomposable components.Elevated CO₂ had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO₂-C production) and invertase activity. The effects of elevated CO₂ on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO₂, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO₂ enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO₂ on the soil C balance.     

Hormone-induced protection of sunflower photosynthetic apparatus against copper toxicity

The effects of excess Cu as affected by the application of exogenous hormones (gibberellic acid - GA₃ and indole-3-acetic acid - IAA) with respect to sunflower (Helianthus annuus L.) growth, physiology, and metabolism were studied. Application of 100 M IAA lessened the toxic effects of 80 M Cu in roots indicating greater root length and root hair formation, while addition of 100 M GA₃ ameliorated the toxic effect mainly to the shoot. The content of photosynthetic pigments significantly declined under Cu stress, whereas application of hormones led to a substantial preservation of chlorophylls and carotenoids. Under Cu stress, the rate constant of energy trapping by photosystem 2 (PS2) reaction centres (RCs) was reduced as a result of physical dissociation of the light-harvesting complex (LHC) from PS2 core, while application of IAA and especially GA₃ resulted in stability of the LHC of PS2 RCs. The drop in net photosynthetic (PN) and transpiration (E) rates with preserved or slightly reduced variable to maximum fluorescence ratio (F_v/F_m) in the presence of 80 M Cu could be explained by a possible inhibition of the enzymatic processes in the Calvin cycle. Application of 100 M IAA and 100 M GA₃ lessened Cu effects mainly on P _N. Water use efficiency was also improved under hormone exposure.     

Photosynthetic CO2 Fixation in the Second Leaf of Wheat Seedlings Grown at Different Conditions of Nitrogen Nutrition

The rates of photosynthetic ₂ assimilation were determined in fully expanded second leaves of 21-day-old wheat (Triticum aestivum L.) seedlings grown on media supplied with nitrate or ammonia and on a nitrogen-free medium (NO₃ ^–- or NH₄ ⁺-treatments and N-deficit treatment, respectively). The maximal quantum efficiency of photosynthesis was independent on conditions of nitrogen nutrition. When leaves were exposed to 0.03% ₂ and high-intensity light, the lowest photosynthetic rate was noted for N-deficit treatment and the highest rate was characteristic of NH₄ ⁺ treatment. The elevation of the ₂ concentration in the gas phase to 0.1% stimulated photosynthesis at high-intensity light in all treatments. The rate of ₂ uptake by the leaf of N-deficient seedlings increased with ₂ concentration to a larger extent than in other treatments and approached the ₂ uptake rate characteristic of the NO₃ ^– treatment. In plants grown on a nitrogen-free medium, the leaf accumulated lesser amounts of reduced nitrogen and higher amounts of starch, but the content of chloroplast protein corresponded to that of NO₃ ^– treatment. In the leaf of NH₄ ⁺-treated seedlings, the rate of ₂ assimilation was higher than in the leaf of NO₃ ^– treated plants, regardless of the composition of the gas mixture. The ammonium-type nutrition, as compared to the nitrate-type nutrition, elevated the amount of reduced nitrogen in the leaf and promoted accumulation of chlorophyll and protein, the chloroplast protein in particular.     

Temperature effects on the photosynthetic response of C3 plants to long-term CO2 enrichment

To assess the long-term effect of increased CO₂ and temperature on plants possessing the C₃ photosynthetic pathway, Chenopodium album plants were grown at one of three treatment conditions: (1) 23 °C mean day temperature and a mean ambient partial pressure of CO₂ equal to 350 bar; (2) 34 °C and 350 bar CO₂; and (3) 34 °C and 750 bar CO₂. No effect of the growth treatments was observed on the CO₂ reponse of photosynthesis, the temperature response of photosynthesis, the content of Ribulose-1,5-bisphosphate carboxylase (Rubisco), or the activity of whole chain electron transport when measurements were made under identical conditions. This indicated a lack of photosynthetic acclimation in C. album to the range of temperature and CO₂ used in the growth treatments. Plants from every treatment exhibited similar interactions between temperature and CO₂ on photosynthetic activity. At low CO₂ (< 300 bar), an increase in temperature from 25 to 35 °C was inhibitory for photosynthesis, while at elevated CO₂ (> 400 bar), the same increase in temperature enhanced photosynthesis by up to 40%. In turn, the stimulation of photosynthesis by CO₂ enrichment increased as temperature increased. Rubisco capacity was the primary limitation on photosynthetic activity at low CO₂ (195 bar). As a consequence, the temperature response of A was relatively flat, reflecting a low temperature response of Rubisco at CO₂ levels below its k_m for CO₂. At elevated CO₂ (750 bar), the temperature response of electron transport appeared to control the temperature dependency of photosynthesis above 18 °C. These results indicate that increasing CO₂ and temperature could substantially enhance the carbon gain potential in tropical and subtropical habitats, unless feedbacks at the whole plant or ecosystem level limit the long-term response of photosynthesis to an increase in CO₂ and temperature.Abbreviations A net CO₂ assimilation rate - C _a ambient partial pressure of CO₂ - C _i intercellular partial pressure of CO₂ - Rubisco Ribulose-1,5-bisphosphate carboxylase - VPD vapor pressure difference between leaf and air     

Spatial and temporal variation in soil CO2 efflux in an old-growth neotropical rain forest, La Selva, Costa Rica

Our objectives were to quantify and compare soil CO₂ efflux of two dominant soil types in an old-growth neotropical rain forest in the Atlantic zone of Costa Rica, and to evaluate the control of environmental factors on CO₂ release. We measured soil CO₂ efflux from eight permanent soil chambers on six Oxisol sites. Three sites were developed on old river terraces (old alluvium) and the other three were developed on old lava flows (residual). At the same time we measured soil CO₂ concentrations, soil water content and soil temperature at various depths in 6 soil shafts (3 m deep). Between old alluvium sites, the two-year average CO₂ flux rates ranged from 117.3 to 128.9 mg C m^–2 h^–1. Significantly higher soil CO₂ flux occurred on the residual sites (141.1 to 184.2 mg C m^–2 h^–1). Spatial differences in CO₂ efflux were related to fine root biomass, soil carbon and phosphorus concentration but also to soil water content. Spatial variability in CO₂ storage was high and the amount of CO₂ stored in the upper and lower soil profile was different between old alluvial and residual sites. The major factor identified for explaining temporal variations in soil CO₂ efflux was soil water content. During periods of high soil water content CO₂ emission decreased, probably due to lower diffusion and CO₂ production rates. During the 2-year study period inter-annual variation in soil CO₂ efflux was not detected.     

N-andO-alkylation of glycoconjugates and polysaccharides by solid base in dimethyl sulphoxide/alkyl lodide

O-Methylation of simple neutral oligosaccharides is readily accomplished in dimethyl sulphoxide containing solid sodium hydroxide and methyl iodide [Cincanu I, Kerek F (1984) Carbohydr Res 131209-17]. This procedure has been extended to 2-acetamido-2-deoxy sugars and sialic acid-containing oligosaccharides. CompleteO-andN-methylation was in most cases achieved in 15 min. Esterification of carboxylic groups in uronic acids was fast and resulted in concomitant -elimination. The method is also suitable for methylation of glycoproteins and glycosphingolipids. Polysaccharides can also be methylated by this technique. Analysis of the products by gas-liquid chromatography and mass spectrometry showed no degradation products.Abbreviations lacto-N-tetraose LcOse₄, Gal3GlcNAc3Gal4Glc - lacto-N-fucopentaose III III³Fuc-nLcOse₄, Gal4[Fuc3]GlcNAc3Gal4Glc - trihexosylceramide GbOse₃Cer, Gal4Gal4Glc1-1Cer - globoside GbOse₄Cer, GalNAc3Gal4Glc1-1Cer - FAB-MS fas atom bombardment mass spectrometry     

Lactate conversion to acetate,CO2 and H2 in cell suspensions of Desulfovibrio vulgaris (Marburg): indications for the involvement of an energy driven reaction

Cell suspensions of Desulfovibrio vulgaris were found to catalyze, in the absence of sulfate, the complete conversion of 1 lactate to 1 acetate, 1 CO₂, and 2 H₂ (G₀=-8.8 kJ/mol) and of 1 pyruvate to 1 acetate, 1 CO₂, and 1 H₂ (G₀=-52 kJ/mol). Protonophores, the proton translocating ATPase inhibitor N,N-dicyclohexylcarbodiimide, and arsenate specifically inhibited H₂ formation from lactate but not from pyruvate. The results suggest that lactate oxidation to pyruvate and H₂ (G ₀=+43.2 kJ/mol) is energy driven.     

Variability in the 11S globulin fraction of seed storage proteins ofHelianthus (Asteraceae)

The seed storage globulins from sixHelianthus and four hybrids were studied using mono and bidimensional gel SDS electrophoresis (+ 2 mercaptoethanol). The polypeptide composition of each subunit was determined. Different pairs are specifically expressed according to the species studied. Three typical patterns were discriminated. All the studied species exhibit five subunits: two of them are expressed in all the species (₁₁ and ₂₂). The subunit corresponding to the ₁₁ pair is present inH. petiolaris and in the three populations ofH. annuus studied. The _2b2 pair is common toH. annuus andH. argophyllus. H. petiolaris presents two specific _2a2 and ₄₄ pairs andH. annuus a specific ₃₃ pair. InH. argophyllus _{11 33} or ₄₄ are never observed but are replaced by ₁₃ and ₃₁ pairs. Some globulins, poorly represented, are of forms but present chains of higher molecular weights (in the range 54–56 kDa). Expressing variations in the banding patterns between these species by the use of a similarity index reveals complete identity between the three populations ofH. annuus. Identity between the twoH. petiolaris studied is also observed.H. annuus andH. argophyllus appear to be closer to each other thanH. petiolaris concerning the seed storage globulins.     

Elevated CO2 effects on carbon and nitrogen cycling in grass/clover turves of a Psammaquent soil

Effects of elevated CO₂ (525 and 700 L L^–1), and a control (350 L L^–1 CO₂), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further spring period, half of the turves under 350 and 700 L L^–1 were subjected to summer drying and were then re-wetted before a further autumn period; the remaining turves were kept continuously moist throughout these additional three consecutive seasons. The continuously moist turves were then pulse-labelled with ¹⁴C-CO₂ to follow C pathways in the plant/soil system during 35 days.Growth rates of herbage during the first four seasons averaged 4.6 g m^–2 day^–1 under 700 L L^–1 CO₂ and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these seasons averaged 465, 800 and 824 g m^–2 in the control, 525 and 700 L L^–1 treatments, respectively.in continuously moist soil, elevated CO₂ had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO₂-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO₂ produced h^–1 mg^–1 microbial C was about 10% higher in the 700 L L^–1 CO₂ treatment than in the other two treatments. Elevated CO₂ had no clearly defined effects on N availability, or on the net N mineralization of added herbage.In the labelling experiment, relatively more ¹⁴C in the plant/soil system occurred below ground under elevated CO₂, with enhanced turnover of ¹⁴C also being suggested.Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously summer-dried, CO₂ production was again higher, but net N mineralization was lower, under elevated CO₂ than in the control after autumn pasture growth.Over the trial period of 422 days, elevated CO₂ generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.