Effect of darkness and CO2 starvation on NH4+ and NO3− assimilation in the unicellular alga Cyanidium caldarium

Cyanidium caldarium (Tilden) Geitler, a non-vacuolate unicellular alga, resuspended in medium flushed with air enriched with 5% CO₂, assimilated NH₄⁺ at high rates both in the light and in the dark. The assimilation of NO₃⁻, by contrast, was inhibited by 63% in the dark. In cell suspensions flushed with CO₂-free air, NH₄⁺ assimilation decreased with time both in the light and in the dark and ceased almost completely after 90 min. The addition of CO₂ completely restored the capacity of the alga to assimilate NH₄⁺. NO₃⁻ assimilation, by contrast, was 33% higher in the absence of CO₂ and was linear with time. It is suggested that NO₃⁻ and NH₄⁺ metabolism in C. caldarium are differently controlled in response to the light and carbon conditions of the cell.     

Comparative analysis of surface electrostatic potentials of carbon, boron/nitrogen and carbon/boron/nitrogen model nanotubes

We have extended an earlier study, in which we characterized in detail the electrostatic potentials on the inner and outer surfaces of a group of carbon and B_xN_x model nanotubes, to include several additional ones with smaller diameters plus a new category, C_2xB_xN_x. The statistical features of the surface potentials are presented and analyzed for a total of 19 tubes as well as fullerene and a small model graphene. The potentials on the surfaces of the carbon systems are relatively weak and rather bland; they are much stronger and more variable for the B_xN_x and C_2xB_xN_x. A qualitative correlation with free energies of solvation indicates that the latter two categories should have considerably greater water solubilities. The inner surfaces are generally more positive than the corresponding outer ones, while both positive and negative potentials are strengthened by increasing curvature. The outsides of B_xN_x tubes have characteristic patterns of alternating positive and negative regions, while the insides are strongly positive. In the closed C_2xB_xN_x systems, half of the C–C bonds are double-bond-like and have negative potentials above them; the adjacent rows of boron and nitrogens show the usual B_xN_x pattern. When the C_2xB_xN_x tubes are open, with hydrogens at the ends, the surface potentials are dominated by the B⁺–H^– and N^––H⁺ linkages.Figure Calculated electrostatic potential on the molecular surface of closed (6,0) B₄₈N₄₈; a is an outside view, while b shows the interior. Color ranges, in kcal mol^–1: red, greater than 20; yellow, between 20 and 0; green, between 0 and –10; blue, between –10 and –20; purple, more negative than –20     

不同碳源对小球藻Chlorella zofingiensis异养产虾青素的影响

研究了葡萄糖、蔗糖和果糖对小球藻(Chlorella zofingiensis)异养生长及产虾青素的影响,结果表明,在糖浓度为20g/L时,细胞生长较快,但干重较小,虾青素含量较低;在糖浓度为50g/L时,细胞生长较慢,但干重较大,虾青素含量较高。3种碳源中蔗糖和葡萄糖效果较好,在蔗糖浓度为50g/L时,虾青素含量和产量分别达到0.94mg/g和9.61mg/L。     

Influence of O2- and CO2-concentrations on oscillations in the transpiration rate from oat plants in darkness

The effect of changed O₂- and CO₂-concentrations in air on oscillations in the transpiration rate of young oat plants in darkness has been investigated. Lowering the O₂-concentration to 5% did not affect the oscillations. When the CO₂ in the air was removed, the transpiration rate increased, and the oscillations ceased. When the CO₂-concentration was raised to 0.3 or 3% the transpiration rate temporarily decreased, but the period of the oscillations was not changed. Further increase of the CO₂-concentration caused, after a temporary decrease, an increased transpiration rate, and the oscillations eventually ceased. The period of the oscillations was influenced by the temperature: a lower temperature gave a longer period. It is concluded that substomatal O₂-deficit or high CO₂-concentration do not play a crucial role in the origin of these oscillations.     

N,N-dimethylcarbamato complexes of zinc

By reaction of Zn₄O(O₂CNMe₂)₆ (1) with [NH₂Me₂][O₂CNMe₂] in toluene as medium, the homoleptic zinc compound [Zn(O₂CNMe₂)₂] (2) was obtained, which reverted back to the tetranuclear μ-oxo derivative by controlled hydrolysis. The reaction of ZnO in MeCN with an excess of [NH₂Me₂][O₂CNMe₂] in concentrated solution produced high yields of [Zn(O₂CNMe₂)₂] (2) or [NH₂Me₂][Zn₂(O₂CNMe₂)₅] · xMeCN, 3 · xMeCN, x = 1 or 2, depending on the experimental conditions.     

Survival and photosynthetic activity of different Dinophysis acuminata populations in the northern Baltic Sea

This study deals with a recently found phenomenon in the northern Baltic Sea: the occurrence of the dinoflagellate Dinophysis acuminata in the deep water below the thermocline. This was first observed in July 2001 at the station BY 15 in the Gotland Deep, where a sharp and intensive chlorophyll fluorescence signal was encountered at 77 m depth. The fluorescence peak was due to a dinoflagellate community dominated by Dinophysis acuminata (approximately 18 000 cells l⁻¹). The survival of this community was followed in laboratory incubations in low light (20 μE m⁻² s⁻¹) and low temperature (+5 °C). After 5 weeks incubation, 67–84% of the initial cell abundance was lost, while few D. acuminata cells survived up to 24 weeks in the original sample. During the incubation, the fluorescence signal of the cells became fainter and the chloroplasts smaller and aggregated. On two occasions a D. acuminata cell was found attached to a smaller cell by a thin cytoplasm strand, possibly indicating mixotrophic behavior. During the following summer (2002), the photosynthetic efficiency of D. acuminata collected from thermocline layers of few stations and from the nitracline (75–80 m) at one station was studied in photosynthesis irradiance (P–E) incubations. Photosynthetic activity occurred in all populations, with differences in their photosynthetic carbon uptake rates. Photosynthesis of D. acuminata populations was saturated between 250 and 500 μE m⁻² s⁻¹; maximum cell-specific carbon uptake rates (P_m) ranged from 160–925 pg C cell⁻¹ h⁻¹. The P_m-rates in populations originating below the thermocline and in an artificially darkened population were markedly lower than in populations from upper water layers. The varying maximum photosynthetic rates of these populations may reflect their history, e.g. time spent in different light environments.     

Organic matter processing by the shrimp Palaemonetes sp.: Isotopic and elemental effects

Aquatic crustaceans often play a major role in organic matter (OM) transformation and recycling through their feeding and excretory activities. In this study, we measured the isotopic and elemental composition of organic matter fed to Palaemonetes sp. shrimp and the fecal pellets they produced. Nitrogen (N) content of the food (8.2 ± 0.2%, mean ± SD) was significantly higher than the fecal pellets (2.0 ± 0.9%), a pattern that also applied to the carbon (C) content of food (46.7 ± 1.0%) and fecal pellets (14.3 ± 6.8%). We also found a significant decrease in the N content of undigested, macerated food (6.1 ± 0.9 %) relative to food that had been soaked in artificial seawater (ASW) and artificial seawater that had previously contained shrimp (CASW) in the absence of feeding shrimp. We found no significant difference in N or C isotopic composition between the dry food, ASW- and CASW-soaked control food, and fecal pellets. We did, however, observe a significant increase in δ¹⁵N of the undigested, macerated food (δ¹⁵N = 6.3 ± 0.6‰) relative to both the dry flake food (δ¹⁵N = 5.6 ± 0.2‰) and controls incubated in the absence of shrimp in either ASW (δ¹⁵N = 5.6 ±0.3‰) or CASW (δ¹⁵N = 5.8 ± 0.1‰). Our results differ from previous findings of isotopic alteration of OM during processing by crustaceans (copepods), suggesting that isotopic changes related to feeding might be either taxon- or food-specific. This study also provides information on the influence of grazers/shredders on both the elemental and isotopic composition of POM, suggesting that larger aquatic shredders can influence the chemical composition of particles by either physical manipulation of the POM (release of DOM) or by facilitating microbial colonization of the POM.     

A Comparison of CO2 Uptake by the Green Algae Tetraedron minimum and Chlamydomonas monoica

Abstract: The ability of the green alga Tetraedron minimum to acquire inorganic carbon from its environment was investigated and compared with that of Chlamydomonas monoica. T. minimum showed a higher affinity for bicarbonate ions than C. monoica, regardless of whether it was grown at high or low CO₂ concentrations. Furthermore, T. minimum was distinguished by the fact that it maintained a large intracellular pool of inorganic carbon. These features may explain why this alga is able to proliferate in alkaline conditions.     

Uptake and resource allocation of inorganic carbon by the temperate seagrasses Posidonia and Amphibolis

Productivity measurements from carbon uptake have been suggested as good indicators of the physiological health of seagrasses. As seagrasses acquire carbon from the surrounding water, the rate of uptake often provide a good measure of the efficiency at which seagrasses meet their resource demands for growth. This rate is often used to assess the photosynthetic efficiency of the plants, a proxy for the physiological status of seagrass. This has special relevance to the Adelaide region as over 5000 ha of seagrasses have been lost from Adelaide coastal waters over the last 70 years, with much of this loss attributed to nutrient inputs from wastewater, industrial and stormwater discharges. This study used an in-situ inorganic carbon isotope-labelling and spike approach to obtain ecologically relevant estimates of seasonal variability in carbon uptake and its allocation in two species of temperate seagrass common to this coast (Amphibolis antarctica and Posidonia angustifolia). Uptake of carbon by the seagrass complex (leaves, roots, phytoplankton and epiphytes) was affected by both season and species. Carbon uptake rates of phytoplankton were generally higher than other components of the system. Uptake rates ranged from 0.01 mg C g^− 1 DW h^− 1 (summer) to 0.61 mg C g^− 1 DW h^− 1 (spring) in Posidonia and 0.02 mg C g^− 1 DW h^− 1 (summer) to 0.93 mg C g^− 1 DW h^− 1 (winter) in Amphibolis. Carbon uptake by the Amphibolis complex was higher than in the Posidonia complex. The Amphibolis complex had higher uptake rates in summer whereas the Posidonia complex was higher in spring. Fine sediments probably from a nearby dredging operation, are likely to have resulted in lower carbon uptake and a reduction in the above-ground and below-ground biomass in summer.     

Carbohydrate Reserve and Dark Carbon Fixation in the Brown Macroalga, Laminaria hyperborea

Tissue discs originating from young, growing blade areas and from adult, mature frond regions of the brown macroalga Laminaria hyperborea (Fosl.) Gunn. (Phaeophyceae, Laminariales) were investigated with particular regard to photosynthesis, dark respiration, dark carbon fixation, and carbohydrate reserves. It was found that the mannitol/laminaran reserve of the young, developing blade meets the requirements of dark respiratory metabolism for only 7-10d at 10±2 °C under continuous darkness. A concomitant decrease in the potential for (β-carboxylation of phosphoenolpyruvate by phosphoenolpyruvate carboxykinase (EC 4.1.1.32) occurred along with the depletion of the stored carbohydrate. Restoring the intracellular pool of reserve carbohydrates by photosynthesis and by feeding of exogenously supplied mannitol resulted in a short term recovery of the rates of dark fixation. These findings support the view that (i) in the dark the substrate of (β-carboxylation is mainly derived from mannitol (along with glycolytic degradation of laminaran) and (ii) the young blade is not able to maintain its own carbon balance under the environmental conditions during midwinter and early spring, but relies on a carbon flow from the old blade.     

The influence of rapid urbanization and land use changes on terrestrial carbon sources/sinks in Guangzhou,China

Complex changes in carbon sources and sinks caused by rapid urbanization have been observed with extensive changes in the quantity, structure, and spatial pattern of land use types. Based on the modified Carnegie-Ames-Stanford Approach model and on gray relational analysis, we analyzed the influence of land use changes on carbon sinks and emissions in Guangzhou from 2000 to 2012. The aim was to identify suitable options for built-up land expansion that would allow for minimal carbon losses. The key results were as follows: (1) Built-up land increased by 118.91% in Guangzhou city over the study period, with this expansion taking the form of concentric circles extending around the old Yuexiu district. (2) Carbon emissions over the period of analysis significantly exceeded carbon sink capabilities. The total carbon sink decreased by 30.02%, from 535.40 × 10³ t to 374.6 × 10³ t. Total carbon emissions increased by 1.89 times, from 13.73 × 10⁶ t to 39.67 × 10⁶ t; 80% of carbon emissions were derived from energy consumption. (3) There were large differences in the extent of carbon sink losses at different scales of built-up land expansion and land use change. In Guangzhou, the loss of carbon sink is small when cultivated land (though not prime farmland) and water bodies are converted to built-up land on a small scale. The loss of carbon sink is much smaller when grasslands are converted to built-up land on a large scale. However, forested land, which has excellent carbon sink functions, should not be converted. (4) Changes in carbon sinks were mainly affected by natural factors and land urbanization. Changes in carbon emissions were mainly affected by population urbanization, economic urbanization, and land urbanization. (5) To achieve “economical and intensive use of land”, “urban growth boundary” and “ecological red lines” should be determined for government policies on land use management. These factors have great significance for “increasing carbon sinks and reducing carbon emissions” in urban ecological systems.     

Molecular analysis of the interaction between the Bacillus subtilis trehalose repressor TreR and the tre operator

The trehalose operon of Bacillus subtilis is subject to regulation by induction, mediated by the repressor TreR, and by carbon catabolite repression (CCR). For in vitro investigations, TreR from B. subtilis was overproduced and purified. Its molecular mass, as estimated by SDS-PAGE, is 27 kDa. Size fractionation under native conditions yielded a size estimate of 56 kDa, indicating that TreR exists as a dimer in its native state. Analysis of its interaction with various DNA fragments shows that TreR is able to recognize two tre operators with different efficiencies, and indicates cooperative binding. Previous results have suggested that CCR of the tre operon occurs by a mechanism in which the specific regulator, TreR, may be involved independently of the central component, CcpA. The data presented here indicate that the TreR-tre operator interaction is influenced by several effectors. Thus, the presence of trehalose-6-phosphate, as well as glucose-1-phosphate and sodium chloride, inhibits tre operator binding. Glucose-6-phosphate can act as an anti-inducer, which might reflect its additional role in CCR exerted by glucose. Received: 28 April 1998 / Accepted: 8 July 1998     

Nitrogen nutrition of C3 plants at elevated atmospheric CO2 concentrations

The atmospheric CO₂ concentration has risen from the preindustrial level of approximately 290 μl l⁻¹ to more than 350 μl l⁻¹ in 1993. The current rate of rise is such that concentrations of 420 μl l⁻¹ are expected in the next 20 years. For C₃ plants, higher CO₂ levels favour the photosynthetic carbon reduction cycle over the photorespiratory cycle, resulting in higher rates of carbohydrate production and plant productivity. The change in balance between the two photosynthetic cycles appears to alter nitrogen and carbon metabolism in the leaf, possibly causing decreases in nitrogen concentrations in the leaf. This may result from increases in the concentration of storage carbohydrates of high molecular weight (soluble or insoluble) and/or changes in distribution of protein or other nitrogen containing compounds. Uptake of nitrogen may also be reduced at high CO₂ due to lower transpiration rates. Decreases in foliar nitrogen levels have important implications for production of crops such as wheat, because fertilizer management is often based on leaf chemical analysis, using standards estimated when the CO₂ levels were considerably lower. These standards will need to be re-evaluated as the CO₂ concentration continues to rise. Lower levels of leaf nitrogen will also have implications for the quality of wheat grain produced, because it is likely that less nitrogen would be retranslocated during grain filling.     

Effects of elevated CO2 on growth and carbon/nutrient balance in the deciduous woody shrub Lindera benzoin (L.) Blume (Lauraceae)

We examined the effects of elevated CO₂ on growth and carbon/nutrient balance in a natural population of the deciduous temperate zone shrub Lindera benzoin. Our data concern whole plant, leaf, and stem growth for the first two seasons of a long-term field experiment in which CO₂ levels were manipulated in situ. In addition to growth parameters, we evaluated changes in leaf and stem chemistry, including total nitrogen, nonstructural carbohydrates, and total phenolics. Over the course of this study, L. benzoin appeared to respond to elevated CO₂ primarily by physiological and biochemical changes, with only a slight enhancement in aboveground growth (ramet height). Positive effects on aboveground growth were primarily evident in young (nonreproductive) ramets. Our results suggest that nitrogen limitation may have constrained plants to allocate carbohydrates produced in response to elevated CO₂ primarily to storage and belowground growth, and perhaps to increased secondary chemical production, rather than to increased stem and leaf growth. We discuss our results in terms of changes in carbon/nutrient balance induced by elevated CO₂, and provide predictions for future changes in this system based upon constraints imposed by intrinsic and extrinsic factors and their potential effects on the reallocation of stored reserves.     

碳源和氮源对黑盖木层孔菌菌丝生长的影响

研究了四种碳源(蔗糖、乳糖、葡萄糖、可溶性淀粉)和九种氮源(玉米面、麸皮、马铃薯、大豆粉、酵母粉、蛋白胨、硝酸钾、硝酸铵、尿素)对黑盖木层孔菌菌丝生长的影响。从不同代数的菌丝体中提取多糖,并测定多糖含量、分子量分布范围及单糖组成。结果表明:黑盖木层孔菌菌丝生长的最佳碳源为可溶性淀粉,最佳氮源为玉米面,最优碳氮组合为蔗糖和玉米面的组合。不同代数的菌丝体多糖性状基本稳定。     

Respiratory responses of higher plants to atmospheric CO2 enrichment

Although the respiratory response of native and agricultural plants to atmospheric CO₂ enrichment has been reported over the past 75 years, only recently have these effects emerged as prominent measures of plant and ecosystem response to the earth's changing climate. In this review we discuss this rapidly expanding field of study and propose that both increasing and decreasing rates of leaf and whole-plant respiration are likely to occur in response to rising CO₂ concentrations. While the stimulatory effects of CO₂ on respiration are consistent with our knowledge of leaf carbohydrate status and plant metabolism, we wish to emphasize the rather surprising short-term inhibition of leaf respiration by elevated CO₂ and the reported effects of long-term CO₂ exposure on growth and maintenance respiration. As is being found in many studies, it is easier to document the respiratory response of higher plants to elevated CO₂ than it is to assign a mechanistic basis for the observed effects. Despite this gap in our understanding of how respiration is affected by CO₂ enrichment, data are sufficient to suggest that changes in leaf and whole-plant respiration may be important considerations in the carbon dynamics of terrestrial ecosystems as global CO₂ continues to rise. Suggestions for future research that would enable these and other effects of CO₂ on respiration to be unravelled are presented.     

Application of targeted metagenomics to explore abundance and diversity of CO2-fixing bacterial community using cbbL gene from the rhizosphere of Arachis hypogaea

Sequestration of CO₂ by autotrophic bacteria is a key process of biogeochemical carbon cycling in soil ecosystem. Rhizosphere is a rich niche of microbial activity and diversity, influenced by change in atmospheric CO₂. Structural changes in rhizosphere composition influence microbial communities and the nutrient cycling. In the present study, the bacterial diversity and population dynamics were established using cbbL and 16S rRNA gene targeted metagenomics approach from the rhizosphere of Arachis hypogaea. A total of 108 cbbL clones were obtained from the rhizospheric soil which revealed predominance of cbbL sequences affiliated to Rhizobium leguminosarum, Bradyrhizobium sp., Sinorhizobium meliloti, Ochrobactrum anthropi and a variety of uncultured cbbL harboring bacteria. The 16S rRNA gene clone library exhibited the dominance of Firmicutes (34.4%), Proteobacteria (18.3%), Actinobacteria (17.2%) and Bacteroidetes (16.1%). About 43% nucleotide sequences of 16S rRNA gene clone library were novel genera which showed < 95% homology with published sequences. Gene copy number of cbbL and 16S rRNA genes, determined by quantitative real‐time PCR (qRT PCR), was 9.38 ± 0.75 × 10⁷ and 5.43 ± 0.79 × 10⁸ (per g dry soil), respectively. The results exhibited bacterial community structure with high bacterial diversity and abundance of CO₂‐fixing bacteria, which can be explored further for their role in carbon cycling, sustainable agriculture and environment management.     

Effect of CO2, CO2 and Diamox on photosynthesis and photorespiration in Chlamydomonas reinhardtii (green alga) and Anacystis nidulans (Cyanobacterium, blue-green alga)

Photorespiration by Chlamydomonas reinhardtii and Anacystis nidulans was measured as the oxygen inhibition of CO₂ uptake and the CO₂ compensation points. Net photosynthesis was oxygen dependent in Chlamydomonas grown in 5% CO₂, but CO₂ insensitive in cultures bubbled with air. Anacystis, even when cultured in 5% CO₂, exhibited an CO₂ insensitive net photosynthesis. The CO₂ compensation point of Chlamydomonas grown in cultures bubbled with air and Anacystis grown in 5% CO₂ enriched air, were reached shortly after the measurement was begun and the values were very low, less than 10 μl CO₂ 1^?1; while Chlamydomonas grown in 5% CO₂ enriched air for 4 days showed a high, but temporary CO₂ compensation point (60 μl CO₂ 1^?1). After a two hour adaptation in low CO₂, a stable, low CO₂ compensation point was reached. It seems that photorespiration can only be detected by the methods used in this study when the algae are cultured in high CO₂, but a mechanism exists which blocks photorespiration when the green algae are adapted to low CO₂ concentrations. When Chlamydomonas was treated with Diamox, an inhibitor of carbonic anhydrase, after cultivation in low CO₂ (air), the cells behaved as if they had been grown in high CO₂. They showed an oxygen sensitive net photosynthesis and a high CO₂ compensation point. This indicates that carbonic anhydrase plays an important role in the regulation of a measurable photorespiration in Chlamydomonas. The results are discussed in relation to previous observations of photorespiration measured by enzyme assay, metabolic products and gas exchange properties.