High Inorganic Carbon Concentrations Research Articles

Revisiting the Yudongzi microbialites (basal Triassic, northwestern Sichuan, South China): Fabric textures and paleoenvironmental implication

Unusual sedimentary deposits such as stromatolites, thrombolites, dendrolites, and giant ooids are widely distributed in the Permian–Triassic boundary (PTB) successions of shallow platform facies worldwide. These microbial fabrics, however, are rarely present in the same section. The genesis of these PTB microbialites and the oceanographic conditions linking to the end-Permian mass extinction still remain disputed despite intense study. Here, we report a stromatolite-dendrolite-thrombolite-giant ooid association from the PTB beds of the Yudongzi section on the northwestern margin of the Yangtze Platform, South China, which was situated in low latitudes during the Permian-Triassic (P-Tr) transition. The Yudongzi microbialites rest on an irregular contact with underlying Permian bioclastic limestone and are comprised of lower bedded stromatolite, digitate dendrolite, upper bedded stromatolite, and thrombolite units. The bedded stromatolite is characterized by undulating laminated structures and various amalgamated and layered clots. The digitate dendrolite is made up of digitate-like branches, formed by clots distributed in an arched arrangement, and characterized by abundant branching dendroids. The thrombolite displays distinct clotted textures that comprise a mixture of dark-colored microbial fabric and light-colored interstitial sediment. In microbialite, columnar structures identified as Gakhumella-like calcimicrobe are very abundant. Each individual of Gakhumella-like structure has densely arranged segments forming a columnar- to fan-shaped micro-structure. Single segments are arch-shaped and form a thin chamber between segments. Coccoid-like, bacterial clump-like, and other spheroidal aggregates are also commonly present and suggestive of a biogenetic origin for the Yudongzi microbialites. Moreover, distinct aragonite crystal fans are also for the first time found in the PTB microbialites in South China, suggesting that the fans may have resulted from high inorganic carbon concentrations, and thus high levels of carbonate dioxide in the seawater. The Yudongzi microbialites are capped by shelly grainstone and a massive giant oolite, implying that the demise of the Yudongzi microbialites may be due to destruction by strong wave currents in a high energy setting. Some ooids are coated unevenly by micritic laminae (or envelopes) indicating the possibility of a microbe-related origin. These microbial-coated giant ooids, together with the massive microbialites, may imply the long-term of microbial bloom in the oceans immediately after the end-Permian extinction. The co-existence of abundant Gakhumella-like microorganisms and oxygen-dependent invertebrates, together with some coccoid-like spheroids, aragonite cement crystal fans, and pyrite framboids indicative of oxygen-poor conditions, implies that oxygenation state of the PTB microbialites is much more complex than previously recognized, demonstrating need for continued multidisciplinary examination of facies changes associated biotic mass extinction.

Innovative operational strategies in photosynthetic biogas upgrading in an outdoors pilot scale algal-bacterial photobioreactor

Three innovative operational strategies were successfully evaluated to improve the quality of biomethane in an outdoors pilot scale photobioreactor interconnected to an external absorption unit: i) the use of a greenhouse during winter conditions, ii) a direct CO2 stripping in the photobioreactor via air stripping during winter conditions and iii) the use of digestate as make-up water during summer conditions. CO2 concentrations in the biomethane ranged from 0.4% to 6.1% using the greenhouse, from 0.3% to 2.6% when air was injected in the photobioreactor and from 0.4% to 0.9% using digestate as make up water. H2S was completely removed under all strategies tested. On the other hand, CH4 concentrations in biomethane ranged from 89.5% to 98.2%, from 93.0% to 98.2% and from 96.3% to 97.9%, when implementing strategies i), ii) and iii), respectively. The greenhouse was capable of maintaining microalgae productivities of 7.5 g m−2 d−1 during continental weather conditions, while mechanical CO2 stripping increased the pH in order to support an effective CO2 and H2S removal. Finally, the high evaporation rates during summer conditions allowed maintaining high inorganic carbon concentrations in the cultivation broth using centrate, which provided a cost-effective biogas upgrading.

Nutrients recycle and the growth of Scenedesmus obliquus in synthetic wastewater under different sodium carbonate concentrations

This study illustrated the growth of Scenedesmus obliquus and recycle of nutrients in wastewater combined with inorganic carbon under autotrophic conditions. Scenedesmus obliquus was cultivated under different conditions by adding sodium carbonate (Na2CO3) at 15–40 mg l−1 separately in wastewater containing high nitrogen and phosphorus content. The growth characteristics of S. obliquus, pH and dissolved inorganic carbon (DIC) changes of microalgae liquid, the recycle rate of ammonia and phosphorus and lipid content were determined. The changes of pH and DIC showed that S. obliquus could use Na2CO3 to grow, with lipid contents of 18–25%. Among all Na2CO3 concentrations, 20 mg l−1 was the optimum, of which S. obliquus had the highest NH3-N recycle of 52% and recycle of 67%. By the 14th day, its biomass production also reaches the maximum of 0.21 g l−1. However, inorganic carbon fixation rate was inversely proportional to its concentration. Moreover, the biomass was in positive correlation with the Na2CO3 concentration except 20 mg l−1, which provided a possibility that S. obliquus could be acclimatized to adjust to high concentrations of inorganic carbon to promote biomass accumulation and recycle of nutrients.

Inside out: efflux of carbon dioxide from leaves represents more than leaf metabolism.

High concentrations of inorganic carbon in the xylem, produced from root, stem, and branch respiration, travel via the transpiration stream and eventually exit the plant through distant tissues as CO2. Unlike previous studies that focused on the efflux of CO2 from roots and woody tissues, we focus on efflux from leaves and the potential effect on leaf respiration measurements. We labeled transported inorganic carbon, spanning reported xylem concentrations, with 13C and then manipulated transpiration rates in the dark in order to vary the rates of inorganic carbon supply to cut leaves from Brassica napus and Populus deltoides. We used tunable diode laser absorbance spectroscopy to directly measure the rate of gross 13CO2 efflux, derived from inorganic carbon supplied from outside of the leaf, relative to gross 12CO2 efflux generated from leaf cells. These experiemnts showed that 13CO2 efflux was dependent upon the rate of inorganic carbon supply to the leaf and the rate of transpiration. Our data show that the gross leaf efflux of xylem-transported CO2 is likely small in the dark when rates of transpiration are low. However, gross leaf efflux of xylem-transported CO2 could approach half the rate of leaf respiration in the light when transpiration rates and branch inorganic carbon concentrations are high, irrespective of the grossly different petiole morphologies in our experiment.

Competition between cyanobacteria and green algae at low versus elevated CO2: who will win, and why?

Traditionally, it has often been hypothesized that cyanobacteria are superior competitors at low CO2 and high pH in comparison with eukaryotic algae, owing to their effective CO2-concentrating mechanism (CCM). However, recent work indicates that green algae can also have a sophisticated CCM tuned to low CO2 levels. Conversely, cyanobacteria with the high-flux bicarbonate uptake system BicA appear well adapted to high inorganic carbon concentrations. To investigate these ideas we studied competition between three species of green algae and a bicA strain of the harmful cyanobacterium Microcystis aeruginosa at low (100 ppm) and high (2000 ppm) CO2. Two of the green algae were competitively superior to the cyanobacterium at low CO2, whereas the cyanobacterium increased its competitive ability with respect to the green algae at high CO2. The experiments were supported by a resource competition model linking the population dynamics of the phytoplankton species with dynamic changes in carbon speciation, pH and light. Our results show (i) that competition between phytoplankton species at different CO2 levels can be predicted from species traits in monoculture, (ii) that green algae can be strong competitors under CO2-depleted conditions, and (iii) that bloom-forming cyanobacteria with high-flux bicarbonate uptake systems will benefit from elevated CO2 concentrations.

Influences of nanoscale zero valent iron loadings and bicarbonate and calcium concentrations on hydrogen evolution in anaerobic column experiments

The estimation of nanoscale zero-valent iron (nZVI) reactivity after its injection into the subsurface is essential for its application in groundwater remediation. In the present study H2 generation of commercially available nZVI and novel milled nZVI flakes were investigated in column experiments with varying nZVI loads (ranging from 8 to 43 g nZVI per kg sand). H2 evolution rates were determined for column experiments without and with hydrogen carbonate and/or calcium. On average 0.29 mmol H2/L per g Fe0 evolved within the first 30 days in column experiments with spherical, commercial nZVI particles. The H2 evolution developed almost independently of the water matrices applied. The application of nZVI flakes resulted in lower H2 generation rates. In general corrosion rates accelerated linearly with increasing initial amounts of iron. This was evident in experiments with both particle types. Concentration profiles of carbonate and calcium in influent and effluent were used to estimate corrosion products and precipitates. Despite the presence of high concentrations of inorganic carbon, Fe2+ reacted preferably with hydroxide ions to form ferrous hydroxide which is the precursor of magnetite. As a result only minor passivation of the reactive nZVI was observed.

A novel control method for nitritation: The domination of ammonia-oxidizing bacteria by high concentrations of inorganic carbon in an airlift-fluidized bed reactor

A novel nitritation method based on the addition of inorganic carbon (IC) was verified using an airlift-fluidized bed reactor packed with sponge cubes. A continuous-treatment experiment demonstrated that the type of nitrification—nitrite or nitrate accumulation—could be controlled by the addition of different alkalinity sources (NaHCO 3 or NaOH, respectively). The maximum rate of ammonia oxidation at 30 °C was 2.47 kg-N/(m 3 d), with nitrate formation of less than 0.5% of the converted ammonia. Nitrite accumulation of over 90% was maintained stably over 250 days at 30 °C and was achieved even at 19 °C. Qualitative and quantitative shifts of nitrifying bacteria in the biofilm were monitored by real-time PCR and T-RFLP analysis. Ammonia-oxidizing bacteria (AOB) were dominant but nitrite-oxidizing bacteria (NOB) were eliminated in the reactor when NaHCO 3 was used as the alkalinity source. From the kinetic data, we inferred that high IC concentrations drive stable nitritation by promoting a higher growth rate for AOB than for NOB.

Isolation and characterization of mutants of two diazotrophic cyanobacteria tolerant to high concentrations of inorganic carbon

Diazotrophic heterocystous cyanobacteria Nostoc calcicola and Anabaena sp. ARM 629 were investigated for their ability to grow in presence of sodium bicarbonate (NaHCO3) or carbon dioxide (CO2) under cultural conditions. Maximum growth was observed in 75 mM NaHCO3 and 5% CO2 in N. calcicola and Anabaena ARM 629, respectively. Although their growth rate declined, N. calcicola and Anabaena sp. could tolerate upto 250 mM NaHCO3 and 20% CO2, respectively. N-methyl-N'-nitro N nitrosoguanidine induced mutants of these cyanobacteria were isolated which showed growth upto 1 M NaHCO3 (N. calcicola) or 50% CO2 (Anabaena sp.) in comparison to their wild types. The mutants also showed cross-resistance to either of the inorganic carbon compounds, which was not observed for wild type. It was concluded that mutants were altered in multiple properties enabling them to grow at elevated levels of inorganic carbon compounds.

Competition between Chara aspera and Potamogeton pectinatus as a function of temperature and light

Two experiments were carried out to study the interaction between Chara aspera Deth. ex Willd. and Potamogeton pectinatus L. The purpose of the first experiment was to assess the effect of temperature on the rate of emergence and the second was designed to study the effect of light on the competition during the established phase. P. pectinatus tubers sprouted after about 4 days at 16°C and 9 days at 10°C, which was sooner than either oospores or bulbils of C. aspera (about 15 days at 16°C and 27 days at 10°C). When the irradiance was 36 μmol m −2 s −1, the ash-free dry weight biomass of both species was about 80% lower than at 416 μmol m −2 s −1 and the biomass was not affected by neighbouring plants. However, in the higher light treatment the presence of P. pectinatus suppressed the biomass of C. aspera by maximally 63%. The individual biomass of P. pectinatus at high initial plant densities was reduced by maximally 70% by other plants of the same species, but was not affected by C. aspera. It is concluded that P. pectinatus rather than C. aspera has an advantage in the phase of emergence during spring. Furthermore, under higher light conditions and high inorganic carbon concentrations P. pectinatus may be a better competitor for light than C. aspera, because of its canopy placement near the water surface.

Effect of inorganic carbon supply on the photosynthetic physiology of Gracilaria tenuistipitata

Gracilaria tenuistipitata Zhang et Xia was cultured for 15 d at low, normal and high inorganic carbon concentrations under constant light, temperature and nutrient conditons. Carbonic anhydrase (CA; EC 4.2.1.1.) activity, ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco; EC 4.1.1.39) content, pigment content and C/N ratio were measured, and also the photosynthesis and growth rates. Both Rubisco content and CA activity increased under conditions of low inorganic carbon (Ci) but decreased at high Ci with respect to the control. The amount of pigments declined considerably at high Ci and was slightly higher at low Ci. The maximum rate of photosynthesis and the photosynthetic efficiency increased in low Ci and the opposite was found at high Ci concentration. The effects of Ci concentration on maximum rate of photosynthesis and photosynthetic efficiency are discussed in relation to the variation in pigment and Rubisco contents and CA activity. The data indicate that Ci may be an important factor controlling the photosynthetic physiology of G. tenuistipitata with regard, not only to the enzymes of Ci metabolism, but also to the pigment content.

Circadian rhythm and fast responses to blue light of photosynthesis in Ectocarpus (Phaeophyta, Ectocarpales)

Photosynthesis of Ectocarpus siliculosus (Dillwyn) Lyngb. under continuous saturating red irradiation follows a circadian rhythm. Blue-light pulses rapidly stimulate photosynthesis with high effectiveness in the troughs of this rhythm but the effectiveness of such pulses is much lower at its peaks. In an attempt to understand how blue light and the rhythm affected photosynthesis, the effects of inorganic carbon on photosynthetic light saturation curves were studied under different irradiation conditions. The circadian rhythm of photosynthesis was apparent only at irradiances which were not limiting for photosynthesis. The same was found for blue-light-stimulated photosynthesis, although stimulation was observed also under very low red-light irradiances after a period of adaptation, provided that the inorganic-carbon concentration was not in excess. Double-reciprocal plots of light-saturated photosynthetic rates versus the concentration of total inorganic carbon (up to 10 mM total inorganic carbon) were linear and had a common constant for half-saturation (3.6 mM at pH 8) at both the troughs and the peaks of the rhythm and before and after blue-light pulses. Only at very low carbon concentrations was a clear deviation found from these lines for photosynthesis at the rhythm maxima (red and blue light), which indicated that the strong carbon limitation specifically affected photosynthesis at the peak phases of the rhythm. Very high inorganic carbon concentrations (20 mM) in the medium diminished the responses to blue light, although they did not fully abolish them. The kinetics of the stimulation indicate that the rate of photosynthesis is affected by two blue-light-dependent components with different time courses of induction and decay. The faster component seemed to be at least partially suppressed at red-light irradiances which were not saturating for photosynthesis. Lowering the pH of the medium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates that Ectocarpus takes up free CO2 only and not bicarbonate, although additional physiological mechanisms may enhance the availability of CO2.

HCO 3− use and evidence for a carbon concentrating process in the mat-forming cyanophyte Lyngbya birgei G.M. Smith

The macroscopic cyanophyte Lyngbya birgei G.M. Smith can form extensive floating mats and become an aquatic weed. This organism, when grown in the laboratory under low or relatively high inorganic carbon concentrations (0.1 or 1.0 mM HCO 3 −, representing a range found in nature), showed photosynthetic K 1/2 values for inorganic carbon of 20 and 40 μM when using mainly CO 2 (pH 5.5) and HCO 3 − (pH 9.0), respectively. Comparisons of photosynthetic rates and maximal uncatalyzed HCO 3 − dehydration rates indicated HCO 3 − uptake at the higher pH. Only at an unnaturally high inorganic carbon growth concentration (10 mM) did the affinity for HCO 3 − decrease. Inorganic carbon was concentrated internally in Lyngbya up to eight times external levels by a light and HCO 3 − (but apparently not CO 2) dependent process. Internal inorganic carbon levels were about 2 mM at a range of ambient inorganic carbon concentrations occurring in mats. It is suggested that a resulting elevated internal CO 2 level is the basis for the ability of this cyanophyte to suppress photorespiration. The efficient use of HCO 3 − and the capability to concentrate inorganic carbon are seen as adaptive features which optimize photosynthetic production of Lyngbya in mats, where HCO 3 − is the principal external carbon source available for photosynthesis and O 2 levels are high during the day.

Studies on the carbonic anhydrase activity in Synechocystis PCC6803 wild type and an acetazolamide-resistant mutant

The problem of the role and the localization of carbonic anhydrase activity in cyanobacteria has been addressed by two approaches using strain Synechocystis PCC6803. Physiological analysis of the differential effects of carbonic anhydrase inhibitors on the entry and accumulation of CO2 in cells grown under low or high inorganic carbon concentrations and determination of carbonic anhydrase activities in cellular subfractions led to the hypothesis of the presence of two different enzymes in this strain. This conclusion is compatible with current models. Only the internal enzyme could be regulated by variations of the external inorganic carbon concentrations. A parallel analysis of a mutant of this strain resistant to the inhibitor acetazolamide supported the hypothesis of the presence of two enzymes. This clone would be selectively impaired in the carbonic anhydrase activity involved in the maintenance of the internal CO2 pool, while its transport capacity is unchanged. Key words: carbonic anhydrase, physiological role, localization, inhibitors, cyanobacteria, mutant.

Photosystem-I-driven inorganic carbon transport in the cyanobacterium, Anacystis nidulans

Anacystis nidulans grown at air levels of CO 2 accumulates high concentrations of inorganic carbon within the cells, which effluxes as CO 2 after a light period. The effect of inhibitors and electron acceptors of photosynthesis on the postillumination CO 2 burst was studied to identify the photosynthetic reaction(s) involved in the inorganic carbon transport. The following results were obtained. (i) In the presence of iodoacetamide, an inhibitor of CO 2 fixation, the CO 2 burst was greater and was insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The inorganic carbon accumulation in the presence of iodoacetamide showed an action spectrum of Photosystem (PS) I reaction. The results demonstrate that a PS-I-mediated cyclic electron flow is involved in the inorganic carbon transport. (ii) Draining of electrons to 2,5-dimethyl- p-benzoquinone (DMQ), p-nitrosodimethylaniline (PNDA), O 2 or nitrite and phenazinemethosulfate (PMS)-bypassed cyclic electron flow inhibited the CO 2 burst. This is ascribed to the inhibition of the cyclic electron flow involved in the inorganic carbon transport. (iii) The electron flow to DMQ and PNDA or PMS-bypassed cyclic electron flow produced ATP actively. Thus, the inorganic carbon transport does not proceed by ATP supply only. (iv) Uncouplers and inhibitors of ATP synthesis had a strong inhibitory effect on the CO 2 burst. From these results, we concluded that both PS-I-cyclic electron flow and ATP are required to drive the inorganic carbon transport.

Inorganic carbon limited growth kinetics of some freshwater algae

The inorganic carbon limited growth kinetics were determined for three green and three blue-green algae over a range of light and temperatures. Anabaena flos aquae was found to be the only algae to grow at 39°C. Selenastrum capricornutum and Scenedesmus quadricauda were favored at low temperatures with Selenastrum growing best at high light and carbon levels while Scenedesmus was the most rapidly growing algae under low light, carbon and temperature conditions. Chorella was the fastest growing alga at temperatures from 27 to 33°C under all light and inorganic carbon concentrations. Neither Oscillatoria nor Microcoleus were found to be the dominant algae under the conditions tested. However, under reduced light and temperature conditions, Oscillatoria grew well at high inorganic carbon concentrations.