Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Optimization of aeration for biodiesel production by <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> grown in municipal wastewater

Despite the significant breakthroughs in research on microalgae as a feedstock for biodiesel, its production cost is still much higher than that of fossil diesel. One possible solution to overcome this problem is to optimize algal growth and lipid production in wastewater. The present study examines the optimization of pretreatment of municipal wastewater and aeration conditions in order to enhance the lipid productivity of Scenedesmus obliquus. Results showed that no significant differences were recorded in lipid productivity of S. obliquus grown in primary settled or sterilized municipal wastewater; however, ultrasound pretreatment of wastewater significantly decreased the lipid production. Whereas, aeration rates of 0.2 vvm significantly increased lipid content by 51 %, with respect to the non-aerated culture, which resulted in maximum lipid productivity (32.5 mg L^?1 day^?1). Furthermore, aeration enrichment by 2 % CO₂ resulted in increase of lipid productivity by 46 % over the CO₂ non-enriched aerated culture. Fatty acid profile showed that optimized aeration significantly enhanced monounsaturated fatty acid production, composed mainly of C18:1, by 1.8 times over the non-aerated S. obliquus culture with insignificant changes in polyunsaturated fatty acid proportion; suggesting better biodiesel characteristics for the optimized culture.     

Productivity and biochemical composition of <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> and <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>: effects of different cultivation approaches

The present work evaluated biomass productivity, carbon dioxide fixation rate, and biochemical composition of two microalgal species, Phaeodactylum tricornutum (Bacillariophyta) and Tetradesmus obliquus (Chlorophyta), cultivated indoors in high-technology photobioreactors (HT-PBR) and outdoors both in pilot ponds and low-technology photobioreactors in a greenhouse in southern Italy. Microalgae were grown in standard media, under nitrogen starvation, and in two liquid digestates obtained from anaerobic digestion of agro-zootechnical and vegetable biomass. P. tricornutum, cultivated in semi-continuous mode in indoor HT-PBRs with standard medium, showed a biomass productivity of 21.0?±?2.3 g m^?2 d^?1. Applying nitrogen starvation, the lipid productivity increased from 2.3 up to 4.5?±?0.5 g m^?2 d^?1, with a 24 % decrease of biomass productivity. For T. obliquus, a biomass productivity of 9.1?±?0.9 g m^?2 d^?1 in indoor HT-PBR was obtained using standard medium. Applying liquid digestates as fertilizers in open ponds, T. obliquus gave a biomass productivity (10.8?±?2.0 g m^?2 d^?1) not statistically different from complete medium such as P. tricornutum (6.5?±?2.2 g m^?2 d^?1). The biochemical data showed that the fatty acid composition of the microalgal biomass was affected by the different cultivation conditions for both microalgae. In conclusion, it was found that the microalgal productivity in standard medium was about doubled in HT-PBR compared to open ponds for P. tricornutum and was about 20 % higher for T. obliquus.     

<Emphasis Type="Italic">Artemisia frigida</Emphasis> and <Emphasis Type="Italic">Stipa krylovii</Emphasis>, two dominant species in Inner Mongolia steppe,differed in their responses to elevated atmospheric CO<Subscript>2</Subscript> concentration

Aims

Despite extensive studies on effects of elevated CO₂ concentration ([CO₂]_e) on plant growth, few studies have investigated the responses of native grassland plant species to [CO₂]_e in terms of nutrient acquisition.

Methods

The effects of [CO₂]_e (769 ± 23 ppm) on Artemisia frigida and Stipa krylovii, two dominant species in Inner Mongolia steppe were investigated by growing them for 7 weeks in Open-Top Chambers (OTC).

Results

Exposure to [CO₂]_e enhanced shoot and root growth of A. frigida and S. krylovii. Elevated [CO₂] increased photosynthetic rates (Pn) by 34 % in A. frigida but decreased Pn by 52 % in S. krylovii. Moreover, root-secreted acid phosphatase activity in A. frigida was stimulated by [CO₂]_e, while exudation of malate from roots of S. krylovii was suppressed by [CO₂]_e. Exposure to [CO₂]_e led to a decrease in P concentration in shoots and roots of A. frigida and S. krylovii, but total amount of P accumulated in shoots and roots of both species was increased by [CO₂]_e.

Conclusions

The two dominant species in temperate steppes differed in their responses to [CO₂]_e, such that A. frigida was more adapted to [CO₂]_e than S. krylovii under low availability of soil P.

     

The growth of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> as influenced by CO<Subscript>2</Subscript>, light,and flue gases

In order to achieve recognition as environmentally friendly production, flue gases should be used as a CO₂ source for growing the microalgae Chlorella sorokiniana when used for hydrogen production. Flue gases from a waste incinerator and from a silicomanganese smelter were used. Before testing the flue gases, the algae were grown in a laboratory at 0.04, 1.3, 5.9, and 11.0 % (v/v) pure CO₂ gas mixed with fresh air. After 5 days of growth, the dry biomass per liter algal culture reached its maximum at 6.1 % CO₂. A second experiment was conducted in the laboratory at 6.2 % CO₂ at photon flux densities (PFD) of 100, 230, and 320 μmol photons m^?2 s^?1. After 4 days of growth, increasing the PFD increased the biomass production by 67 and 108 % at the two highest PFD levels, as compared with the lowest PFD. A bioreactor system containing nine daylight-exposed tubes and nine artificial light-exposed tubes was installed on the roof of the waste incinerator. The effect of undiluted flue gas (10.7 % CO₂, 35.8 ppm NO _x , and 38.6 ppm SO₂), flue gas diluted with fresh air to give 4.2 % CO₂ concentration, and 5.0 % pure CO₂ gas was studied in daylight (21.4?±?9.6 mol photons m^?2 day^?1 PAR, day length 12.0 h) and at 135 μmol photons m^?2 s^?1 artificial light given 24 h day^?1 (11.7?±?0.0 mol photons m^?2 day^?1 PAR). After 4 days’ growth, the biomass production was the same in the two flue gas concentrations and the 5 % pure CO₂ gas control. The biomass production was also the same in daylight and artificial light, which meant that, in artificial light, the light use efficiency was about twice that of daylight. The starch concentration of the algae was unaffected by the light level and CO₂ concentration in the laboratory experiments (2.5–4.0 % of the dry weight). The flue gas concentration had no effect on starch concentration, while the starch concentration increased from about 1.5 % to about 6.0 % when the light source changed from artificial light to daylight. The flue gas from the silicomanganese smelter was characterized by a high CO₂ concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NO _x , and 1 ppm SO₂. The biomass production using flue gas significantly increased as compared with about 5 % pure CO₂ gas, which was similar to the biomass produced at a CO₂ concentration of 10–20 % mixed with N₂. Thus, the enhanced biomass production seemed to be related to the low oxygen concentration rather than to the very high CO₂ concentration.     

Carbon dioxide and poultry waste utilization for production of polyhydroxyalkanoate biopolymers by <Emphasis Type="Italic">Nostoc muscorum</Emphasis> Agardh: a sustainable approach

The new paradigm is to view wastes as resources for sustainable development. In this regard, the feasibility of poultry waste and CO₂ utilization for cultivation of a filamentous nitrogen-fixing cyanobacterium, Nostoc muscorum Agardh, was investigated for production polyhydroxyalkanoates, the biodegradable polymers. This cyanobacterium showed profound rise in biomass yield with up to 10 % CO₂ supply in airstream with an aeration rate of 0.1 vvm. Maximum biomass yield of 1.12 g L^?1 was recorded for 8 days incubation period, thus demonstrating a CO₂ biofixation rate of 0.263 g L^?1 day^?1 at 10 % (v/v) CO₂-enriched air. Poultry litter (PL) supplementation also had a positive impact on the biomass yield. The nutrient removal efficiency of N. muscorum was reflected in the significant reduction in nutrient load of PL over the experimental period. A maximum poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) [P(3HB-co-3HV)] copolymer yield of 774 mg L^?1 (65 % of dry cell wt.), the value almost 11-fold higher than the control, was recorded in 10 g L^?1 PL-supplemented cultures with 10 % CO₂ supply under the optimized condition, thus demonstrating that N. muscorum has good potential for CO₂ biomitigation and poultry waste remediation while simultaneously producing eco-friendly polymers.     

Interacting effects of elevated atmospheric CO<Subscript>2</Subscript> and hydrology on the growth and carbon sequestration of <Emphasis Type="Italic">Sphagnum</Emphasis> moss

Peatlands are a critical carbon store comprising 30% of the Earth’s terrestrial soil carbon. Sphagnum mosses comprise up to 90% of peat in the northern hemisphere but impacts of climate change on Sphagnum mosses are poorly understood, limiting development of sustainable peatland management and restoration. This study investigates the effects of elevated atmospheric CO₂ (eCO₂) (800 ppm) and hydrology on the growth of Sphagnum fallax, Sphagnum capillifolium and Sphagnum papillosum and greenhouse gas fluxes from moss–peat mesocosms. Elevated CO₂ levels increased Sphagnum height and dry weight but the magnitude of the response differed among species. The most responsive species, S. fallax, yielded the most biomass compared to S. papillosum and S. capillifolium. Water levels and the CO₂ treatment were found to interact, with the highest water level (1 cm below the surface) seeing the largest increase in dry weight under eCO₂ compared to ambient (400 ppm) concentrations. Initially, CO₂ flux rates were similar between CO₂ treatments. After week 9 there was a consistent three-fold increase of the CO₂ sink strength under eCO₂. At the end of the experiment, S. papillosum and S. fallax were greater sinks of CO₂ than S. capillifolium and the ? 7 cm water level treatment showed the strongest CO₂ sink strength. The mesocosms were net sources of CH₄ but the source strength varied with species, specifically S. fallax produced more CH₄ than S. papillosum and S. capillifolium. Our findings demonstrate the importance of species selection on the outcomes of peatland restoration with regards to Sphagnum’s growth and GHG exchange.     

Verrucarin A and roridin E produced on spinach by <Emphasis Type="Italic">Myrothecium verrucaria</Emphasis> under different temperatures and CO<Subscript>2</Subscript> levels

The behavior of Myrothecium verrucaria, artificially inoculated on spinach, was studied under seven different temperature conditions (from 5 to 35 °C) and under eight different combinations of temperature and CO₂ concentration (14–30 °C and 775–870 or 1550–1650 mg/m³). The isolate used for this study was growing well on spinach, and the mycotoxins verrucarin A and roridin E were produced under all tested temperature and CO₂ conditions. The maximum levels of verrucarin A (18.59 ng/g) and roridin E (49.62 ng/g) were found at a temperature of 26–30 °C and a CO₂ level of 1550–1650 mg/m³. Rises in temperature as well as in temperature and CO₂ concentrations had a significant effect by increasing Myrothecium leaf spots on spinach. The biosynthesis of verrucarin A was significantly increased at the highest temperature (35 °C), while roridin E was influenced by the CO₂ concentration. These results show that a positive correlation between climate condition and macrocyclic trichothecene production is possible. However, because of the ability of M. verrucaria to produce mycotoxins, an increase in temperature could induce the spread of M. verrucaria in temperate regions; this pathogen may gain importance in the future.     

Assessment of <Emphasis Type="Italic">Nannochloropsis gaditana</Emphasis> growth and lipid accumulation with increased inorganic carbon delivery

Algal biomass refineries for sustainable transportation fuels, in particular biodiesel, will benefit from algal strain enhancements to improve biomass and lipid productivity. Specifically, the supply of inorganic carbon to microalgal cultures represents an area of great interest due to the potential for improved growth of microalgae and the possibility for incorporation with CO₂ mitigation processes. Combinations of bicarbonate (HCO₃^?) salt addition and application of CO₂ to control pH have shown compelling increases in growth rate and lipid productivity of fresh water algae. Here, focus was placed on the marine organism, Nannochloropsis gaditana, to investigate growth and lipid accumulation under various strategies of enhanced inorganic carbon supply. Three gas application strategies were investigated: continuous sparging of atmospheric air, continuous sparging of 5% CO₂ during light hours until nitrogen depletion, and continuous sparging of atmospheric air supplemented with 5% CO₂ for pH control between 8.0 and 8.3. These gas sparging schemes were combined with addition of low concentrations (5 mM) of sodium bicarbonate at inoculation and high concentration (50 mM) of sodium bicarbonate amendments just prior to nitrogen depletion. The optimum scenario observed for growth of N. gaditana under these inorganic carbon conditions was controlling pH with 5% CO₂ on demand, which increased both growth rate and lipid accumulation. Fatty acid methyl esters were primarily comprised of C16:0 (palmitic) and C16:1 (palmitoleic) aliphatic chains. Additionally, the use of high concentration (50 mM) of bicarbonate amendments further improved lipid content (up to 48.6%) under nitrogen deplete conditions when paired with pH-controlled strategies.     

Effect of high CO<Subscript>2</Subscript> concentrations on the growth and macromolecular composition of a heat- and high-light-tolerant microalga

A green microalga, Acutodesmus sp., a close relative of Acutodesmus deserticola, was isolated from the wastewater discharges of an oil refinery in India. This study examined the effects of light intensity, temperature, pH, and high-CO₂ treatments (up to 20 %) on the growth of the alga and investigated the effects of different CO₂ treatments on its macromolecular composition (protein, carbohydrate, and lipids). Under controlled laboratory conditions, the alga showed high growth rates over a wide range of light (up to 700 μmol photons m^?2 s^?1), temperature (up to 40 °C), and pH (5–10) conditions. In the stationary phase, the highest protein and carbohydrate content was found to be 71.52 and 40.72 % of dry weight at 5 and 15 % CO₂, respectively. After 5 days of cultivation, the maximum dry weight biomass attained in these cultures was 1.149, 1.99, 1.75, and 1.65 g L^?1 at 5, 10, 15, and 20 % CO₂, respectively, indicating that this strain has significant tolerance to CO₂. These results indicate that this strain is a promising candidate for use in biofixation of CO₂ from the flue gases emitted by industries, and it also has a strong potential as a feedstock for value-added substances.     

Assessing biodegradation of furfuryl alcohol using <Emphasis Type="Italic">Pseudomonas putida</Emphasis> MTCC 1194 and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> MTCC 1034 and its kinetics

The biodegradation of furfuryl alcohol (FA) in shake flask experiments using a pure culture of Pseudomonas putida (MTCC 1194) and Pseudomonas aeruginosa (MTCC 1034) was studied at 30 °C and pH 7.0. Experiments were performed at different FA concentrations ranging from 50 to 500 mg/l. Before carrying out the biodegradation studies, the bacterial strains were acclimatized to the concentration of 500 mg/l of FA by gradually raising 100 mg/l of FA in each step. The well acclimatized culture of P. putida and P. aeruginosa degraded about 80 and 66% of 50 mg/l FA, respectively. At higher concentration of FA, the percentage of FA degradation decreased. The purpose of this study was to determine the kinetics of biodegradation of FA by measuring biomass growth rates and concentration of FA as a function of time. Substrate inhibition was calculated from experimental growth parameters using the Haldane equation. Data for P. putida were determined as µ _max ?=?0.23 h^?1, K _s ?=?23.93 mg/l and K _i ?=?217.1 mg/l and for P. aeruginosa were determined as µ _max ?=?0.13 h^?1, K _s ?=?21.3 mg/l and K _i ?=?284.9 mg/l. The experimental data were fitted in Haldane, Aiba and Edwards inhibition models.     

Carbon Dioxide and Methane Fluxes From Tree Stems,Coarse Woody Debris,and Soils in an Upland Temperate Forest

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m^?2 s^?1, mean ± 1 SD) and net sinks of CH₄ (?2.17 ± 1.60 nmol m^?2 s^?1). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m^?2 s^?1) and net CH₄ sink, but with large uncertainty (?0.27 ± 1.04 nmol m^?2 s^?1) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m^?2 s^?1), but also net CH₄ sources (up to 0.98 nmol m^?2 s^?1), with a mean of 0.11 ± 0.21 nmol m^?2 s^?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.     

High biomass production and CO<Subscript>2</Subscript> fixation from biogas by <Emphasis Type="Italic">Chlorella</Emphasis> and <Emphasis Type="Italic">Scenedesmus</Emphasis> microalgae using tequila vinasses as culture medium

Tequila vinasses (TVs) generated during Tequila production are brown liquid residues rich in nutrients. The nutrient content of agro-industrial effluents represents an excellent resource to support low-cost biomass production of microalgae; nonetheless, it is crucial to select the suitable microalgal strain to attain the highest biomass production in each residue used. In this study, biomass production, CO₂ fixation from biogas, and cell compound accumulation by Chlorella vulgaris U162, Chlorella sp., Scenedesmus obliquus U169, and Scenedesmus sp. using biodigested and filtered TVs as culture medium were evaluated and compared with the conventional microalgal culture media, C30, BG-11, Bold 3N, and Bristol. The four microalgae evaluated attained the highest biomass production and CO₂ fixation rate cultured in both residues, accumulating mainly carbohydrates and proteins although the most appropriate microalga to be cultured in TVs was Chlorella sp., recording 2.30 g L^?1. Moreover, the nutrient ratio of filtered TVs was ideal to support biomass production while biodigested TVs need to be supplemented with nitrogen. Overall, these results demonstrated that tequila vinasses are an excellent resource to support high and quick biomass production of microalgae, which can be used to obtain biofuels as ethanol, biogas, and supplement food depicting an extra benefit during the appropriate disposal of this residue.     

Enantioconvergent hydrolysis of racemic styrene oxide at high concentration by a pair of novel epoxide hydrolases into (<Emphasis Type="Italic">R</Emphasis>)-phenyl-1,2-ethanediol

Objectives

To prepare (R)-phenyl-1,2-ethanediol ((R)-PED) with high enantiomeric excess (ee _p) and yield from racemic styrene oxide (rac-SO) at high concentration by bi-enzymatic catalysis.

Results

The bi-enzymatic catalysis was designed for enantioconvergent hydrolysis of rac-SO by a pair of novel epoxide hydrolases (EHs), a Vigna radiata EH3 (VrEH3) and a variant (AuEH2^A250I) of Aspergillus usamii EH2. The simultaneous addition mode of VrEH3 and AuEH2^A250I, exhibiting the highest average turnover frequency (aTOF) of 0.12 g h^?1 g^?1, was selected, by which rac-SO (10 mM) was converted into (R)-PED with 92.6% ee _p and 96.3% yield. Under the optimized reaction conditions: dry weight ratio 14:1 of VrEH3-expressing E. coli/vreh3 to AuEH2^A250I-expressing E. coli/Aueh2 ^A250I and reaction at 20 °C, rac-SO (10 mM) was completely hydrolyzed in 2.3 h, affording (R)-PED with 98% ee _p. At the weight ratio 0.8:1 of rac-SO to two mixed dry cells, (R)-PED with 97.4% ee _p and 98.7% yield was produced from 200 mM (24 mg/ml) rac-SO in 10.5 h.

Conclusions

Enantioconvergent hydrolysis of rac-SO at high concentration catalyzed by both VrEH3 and AuEH2^A250I is an effective method for preparing (R)-PED with high ee _p and yield.

     

Parasitism Rate of <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> to <Emphasis Type="Italic">Ephestia kuehniella</Emphasis> Larvae: Residual Effect of Deltamethrin,Fenvalerate and Azadirachtin

Sublethal concentrations of chemical insecticides may cause changes in some behavioral characteristics of natural enemies such as functional responses. The residual effect of three synthetic insecticides including deltamethrin, fenvalerate and azadirachtin were studied on functional response of Habrobracon hebetor Say to Ephestia kuehniella Zeller larvae. Seven host densities (2, 4, 8, 16, 32, 64 and 96) were used during a 24 h period. The resulting data were appropriately fit to Type II functional response models in all treatments: (1) control (0.0916 h^?1; and T _h  = 0.2011 h); (2) deltamethrin (a = 0.0839 h^?1; and T _h  = 0.3560 h); (3) fenvalerate (a = 0.0808 h^?1 and T _h  = 0.3623 h); and (4) azadirachtin (a = 0.0900 h^?1 and T _h  = 0.2042 h). Maximum theoretical parasitism rate (T/T _h ) was 119.34 estimated for control wasps. There was no significant difference between the values of attack rates (a and a + D _a ) in all treatments while the handling time was statistically affected in female wasps treated with fenvalerate. Our findings will be useful in safe application of these insecticides in pest management programmes.     

Carbon dioxide as an under-ice lethal control for invasive fishes

Resource managers need effective tools to control invasive fish populations. In this study, we tested under-ice carbon dioxide (CO₂) injection as a novel piscicide method for non-native Silver Carp (Hypophthalmichthys molitrix), Bighead Carp (Hypophthalmichthys nobilis), Grass Carp (Ctenopharyngodon idella), Common Carp (Cyprinus carpio) and native Bigmouth Buffalo (Ictiobus cyprinellus). Fish were held overwinter in nine outdoor ponds (0.04 ha surface area; 340,000 L volume) treated with no CO₂ (control), 43.5–44.0 kg CO₂ (low treatment), and 87.5–88.5 kg CO₂ (high treatment). Ponds were harvested immediately after ice-out to assess survival and condition. Resulting survival in low (mean = 32%) and high (mean = 5%) CO₂-treated ponds was significantly lower than untreated control ponds (mean = 84%). Lethal efficacy varied across species with no Bighead Carp, Silver Carp, or Bigmouth Buffalo surviving the high CO₂ treatment. External infections were observed more frequently after CO₂ treatments (means = 49–67%) relative to untreated ponds (mean = 2%), suggesting a secondary mechanism for poor survival. This study demonstrates that CO₂ can be used as a lethal control for invasive fishes, but effectiveness may vary by species and CO₂ concentration.     

Effects of Gamma Stress and Carbon Dioxide on Eight Bioactive Flavonoids and Photosynthetic Efficiency in <Emphasis Type="Italic">Centella asiatica</Emphasis>

Increased atmospheric CO₂ and gamma irradiation have a significant impact on the plant photosynthetic apparatus and organic compound production. In this study, we evaluated the effect of elevated CO₂ on the photosynthetic efficiency and production of defensive secondary metabolites (flavonoids) induced by gamma irradiation as a physical elicitor in Centella asiatica. Irradiated and non-irradiated 10-week-old plants of C. asiatica were exposed to 400 and 800 μmol mol^?1 of atmospheric CO₂ in growth chambers for 2 h every day until six weeks. A CO₂-enriched atmosphere initially improved the photosynthetic efficiency and ameliorated the detrimental impact of gamma irradiation on the photosynthetic apparatus, increasing carbon allocation into the flavonoid pathway. Elevated CO₂ combined with gamma irradiation resulted in the highest concentration of flavonoids in C. asiatica tissues compared with the other treatments. There was an enhancement in rutin (2.49 fold), naringin (2.15 fold), fisetin (4.07 fold), and morin (4.62 fold) with rising CO₂ concentrations from 400 to 800 μmol mol^?1 in the irradiated plants. With increasing CO₂ concentration, the compensation point and the respiration declined, whereas the apparent quantum yield and the maximum net photosynthesis (A _max) rate increased. The efficiency of photosystem II (PSII) was improved in the irradiated plants grown under high concentrations of CO₂. The total carbohydrate concentration reached the maximum value at the highest level of CO₂, followed by gamma irradiation combined with the highest level of CO₂. Irradiated plants of C. asiatica grown under elevated CO₂ could be superior to non-irradiated plants due to increased carbon availability both for the flavonoid biosynthesis and for the photosynthetic pathway.     

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

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

Comparison of the culture and harvesting of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> for the removal of pharmaceuticals from water

The objective of this work was to assess and compare the removal efficiency of paracetamol and salicylic acid from aqueous medium by a microalgae-based treatment, using either Chlorella vulgaris or Tetradesmus obliquus. Moreover, considering microalgae application in wastewater treatment, the influence of these pharmaceuticals in the algal nutrient removal capacity was evaluated. The removal of paracetamol by T. obliquus (>40 %) was larger than by C. vulgaris (>21 %) in batch culture, and this was also observed for salicylic acid (>93 % by T. obliquus and >25 % by C. vulgaris). Both strains removed nutrients (phosphate and nitrate) almost completely by the end of the batch culture, but T. obliquus showed the highest efficiency at the steady state conditions of the semicontinuous culture. In spite of this, under the flocculants here tested, the efficiency in the recovery of biomass was much higher for C. vulgaris. These results highlight the importance of strain selection in the application of microalgae for wastewater treatment and, particularly, for the removal of pharmaceuticals.