Effect Of CO2 Treatment Research Articles

CO2 treatment of recycled concrete aggregates with high mortar contents: From finding optimal treatment condition, quality enhancement, to life cycle assessment

With increasing construction and demolition waste, the demand for recycled concrete aggregates (RCA) has risen, yet their inherent poor-quality limits usage. In response, CO2 treatment has been developed to enhance RCA quality while contributing to CO2 reduction efforts. This study investigates the effect of CO2 treatment on RCA with high mortar contents for sustainable construction applications. Treatment conditions were optimized by evaluating the CO2 consumption ratio and reaction kinetics under various temperatures (10–50°C), pressures (250–1000 kPa), relative humidity (30–70 %), and initial saturation (30–100 %). X-ray imaging confirms carbonation within the mortar, evidenced by increased greyvalues. Environmental assessment of leachate reveals a significant reduction in chromium concentration from 0.18 mg/L to 0.11 mg/L and a decrease in pH from 10.1 to 7.8 after CO2 treatment, suggesting the potential of CO2 conditioning to mitigate the environmental impacts. Mechanical tests, the aggregate crushing value (ACV) test, and the freeze-thaw (FT) resistance test, demonstrate the improved resistance and durability, with a decrease in ACV from 35.5 % to 33.2 % and FT mass loss from 25.1 % to 20.0 %. The life cycle assessment analysis shows that a simplified CO2 treatment achieved a significant reduction of 138.257 kg CO2 eq per ton of RCA compared to the conventional RCA process. These findings highlight the dual benefits of CO2 treatment: enhanced mechanical performance and reduced environmental impact, promoting the use of recycled aggregates in sustainable construction practices.

Effects of CO2 Treatments on Functional Carbon Efficiencies and Growth of Forest Tree Seedlings: A Study of Four Early-Successional Deciduous Species

Atmospheric CO2 levels have been increasing, and these changes may result in differential adaptive responses in both genera and species and highlight the need to increase carbon sequestration. Ecophysiological and morphological responses of four early-successional deciduous species were examined under ambient CO2 (aCO2, 400 ppm) and elevated CO2 (eCO2, 800 ppm) treatments. The four species, all of which are used in restoration, were Alnus viridis subsp. crispa (Ait.) Turrill (green alder), A. incana subsp. rugosa (Du Roi) R.T. Clausen (speckled alder), Betula populifolia (Marshall) (gray birch), and B. papyrifera (Marshall) (white birch); all are from the same phylogenetic family, Betulaceae. We examined biochemical efficiencies, gas exchange, chlorophyll fluorescence, chlorophyll concentrations, foliar nitrogen (N), and growth traits. A general linear model, analysis of variance, was used to analyze the functional carbon efficiency and growth differences, if any, among genera, species, and provenances (only for growth traits). The alders had greater biochemical efficiency traits than birches, and alders upregulated these traits, whereas birches mostly downregulated these traits in response to eCO2. In response to eCO2, assimilation either remained the same or was upregulated for alders but downregulated for birches. Stomatal conductance was downregulated for all four species in response to eCO2. Intrinsic water use efficiency was greater for alders than for birches. Alders exhibited a consistent upregulation of stem dry mass and height growth, whereas birches were somewhat lower in height and stem dry mass in response to eCO2. Foliar N played an important role in relation to ecophysiological traits and had significant effects relative to genus (alders > birches) and CO2 (aCO2 > eCO2), and a significant genus × CO2 interaction, with alders downregulating foliar N less than did birches. Covariate analysis examining carbon efficiency traits in relation to foliar N showed clear functional responses. Both species in both genera were consistent in their ecophysiological and morphological responses to CO2 treatments. There was supporting evidence that assimilation was sink-driven, which is related to a plant organ’s ability to continue to grow and incorporate assimilates. The alders used in this study are actinorhizal, and the additional available foliar N, paired with increased stem dry mass sink activity, appeared to be driving upregulation of the carbon efficiencies and growth in response to eCO2. Alders’ greater carbon efficiencies and carbon sequestration in impoverished soils demonstrate that alders, as opposed to birches, should be used to accelerate ecological restoration in a world of increasing atmospheric CO2.

Footprint analysis of CO2 in microbial community succession of raw milk and assessment of its quality.

With the growing production of raw milk, interest has been increasing in its quality control. CO2, as a cold processing additive, has been studied to extend the cold storage period and improve the quality of raw milk. However, it is yet uncertain how representative microbial species and biomarkers can succeed one another at distinct critical periods during refrigeration. Therefore, the effects of CO2 treatment on the succession footprint of the microbial community and changes in quality during the period of raw milk chilling were examined by 16S rRNA analysis combined with electronic nose, and electronic tongue techniques. The results indicated that, the refrigeration time was shown to be prolonged by CO2 in a concentration-dependent way. And CO2 treatment was linked to substantial variations in beta and alpha diversity as well as the relative abundances of various microbial taxa (p < 0.01). The dominant bacterial phylum Proteobacteria was replaced with Firmicutes, while the major bacterial genera Acinetobacter and Pseudomonas were replaced with lactic acid bacteria (LAB), including Leuconostoc, Lactococcus, and Lactobacillus. From the perspective of biomarkers enriched in CO2-treated sample, almost all of them belong to LAB, no introduction of harmful toxins has been found. The assessment of the quality of raw milk revealed that CO2 improved the quality of raw milk by lowering the acidity and the rate of protein and fat breakdown, and improved the flavor by reducing the generation of volatiles, and increasing umami, richness, milk flavor and sweetness, but reducing sourness. These findings offer a new theoretical foundation for the industrial use of CO2 in raw milk.

Analysis of CO2 effects on porosity and permeability of shale reservoirs under different water content conditions

CO2 technology has been the key technology to enhance oil and gas recovery for shale oil and gas reservoir development. After injection, CO2 can react with water and generate carbonic acid, which then can react with various minerals in shale, leading to changes of porosity and permeability. However the specific research conclusions remain controversial on whether the effect of CO2 is improvement or damage for porosity and permeability. In CO2 hybrid fracturing, The areas with varied water content are formed due to the difference in mobility. So in this article, we carried out systematic research to clarify the interaction between CO2 and shale in different water content conditions (sufficient water, deficient water and water-free) and draw a pertinent conclusion. And the results show that the effects of CO2 treatment on shale have significant differences among different water content. Under sufficient water conditions, CO2 fully dissolves into water to generate carbonic acid, and large dissolved pores are generated by the massive dissolution of minerals such as feldspar and carbonates in the shale matrix, leading to the increase of porosity and permeability. Under deficient water conditions, only a small amount of carbonic acid is formed after the reaction of CO2 and water, leading to a significant decrease of porosity and permeability. Under water-free conditions, no dissolution is observed on the shale matrix, while some soluble components of organic matter may be extracted by CO2 to form organic pores, leading to slight changes in porosity and permeability. In large scales, although both porosity and permeability in the near-wellbore water-sufficient area is improved, the CO2-affected region presents the overall decline of porosity and permeability, due to the negative effects on the water-deficient area. So, it is necessary to enlarge the volume of water-sufficient areas to get a better effect of enhanced oil and gas recovery.

Changes in Volatile Compounds in Short-Term High CO2-Treated 'Seolhyang' Strawberry (Fragaria × ananassa) Fruit during Cold Storage.

‘Seolhyang’ strawberry is harvested before it is fully ripened and treated with CO2 to extend the shelf-life. However, the volatile changes in the ‘Seolhyang’ strawberry after short-term CO2 treatment have not been investigated, although the volatile profile is an important quality attribute. Herein, we investigated the effect of short-term high CO2 treatment on the changes in the composition of volatile compounds in ‘Seolhyang’ strawberries at two ripening stages (i.e., half-red and bright-red) during cold storage using headspace solid-phase microextraction and gas chromatography-mass spectrometry. Furthermore, the effect of CO2 treatment on fruit quality with respect to the aroma was investigated. A total of 30 volatile compounds were identified. Storage increased the volatile compound concentrations, and the total concentration of volatiles in the CO2-treated strawberries was lower than that of the untreated strawberries during storage. The production of some characteristic strawberry volatiles (e.g., 4-methoxy-2,5-dimethyl-3(2H)-furanone) was inhibited in CO2-treated strawberries. However, CO2 treatment helped maintain the concentrations of hexanal and 2-hexenal, which are responsible for the fresh odor in strawberries. Interestingly, CO2 treatment suppressed the production of off-odor volatiles, acetaldehyde, and hexanoic acid during strawberry storage. Thus, short-term CO2 treatment may help maintain the fresh aroma of strawberries during cold storage.

The Endogenous Metabolic Response of Tribolium castaneum under a High Concentration of CO2

High carbon dioxide concentrations can effectively control most storage pests. To estimate the toxicity effect of high concentrations of CO2, four different concentrations of CO2 (25% CO2, 50% CO2, 75% CO2, and 95% CO2) were used to treat Tribolium castaneum, and the biochemical (carbohydrate content and gene expression level) and physiological (mortality, pupation, eclosion rate, and weight) features of insects submitted to different treatments with CO2 were evaluated. The T. castaneum mortality rate was 50% in approximately 2 days when exposed to a treatment with 95% CO2. When the CO2 concentration exceeded 75%, the pupation rate and eclosion rate of T. castaneum seriously declined. Higher than 25% CO2 concentrations resulted in a lower weight and shrunken body size of T. castaneum. It was further found that different CO2 concentration treatments all influenced the levels of the three carbohydrate contents in T. castaneum. In addition, according to the detection of trehalose metabolism pathway-related genes, T. castaneum mainly responds to stress factors via high expression of TPS, TRE1-2, and TRE1-3. Our results enrich the evaluation of the toxicity effect of CO2 treatment on grain storage pests, providing a basis for further improving the method of regulating grain storage to control insect pests.

Experimental Study on the Impact of CO2 Treatment on Different Lithofacies in Shale Oil Reservoirs

CO2 technology has been progressively used in the development of shale oil. After injection, CO2 can react with formation water to form carbonic acid, which then reacts with carbonate and silicate minerals, resulting in changes in porosity and permeability. However, there are some debates as to whether the effect of CO2 improves or damages porosity and permeability. So, in this paper, systematic experiments were carried out to clarify the interaction between CO2 and shale in different lithofacies and to draw a pertinent conclusion. The results showed that the shale in Qingshankou Formation could be divided into three main lithofacial types: foliaceous shale, laminated feisic shale and laminated diamictic shale. There were relatively more pores, some natural microfractures and small mineral particles in foliaceous shale, a few micropores and large mineral particles in laminated feisic shale, some biogenic calcium carbonate minerals and hardly any micropores in laminated diamictic shale. Due to the diversity of micromorphology and mineral composition, the effects of CO2 treatment had significant differences. For foliaceous shale, CO2 treatment had both improving and damaging effects on porosity and permeability; for laminated shale, both porosity and permeability improved significantly. So, it is necessary to identify the main lithofacies of target formation before the application of CO2 technology in shale oil reservoirs.

Effect of CO2 treatment on the microstructure and properties of steel slag supplementary cementitous materials

Accelerated carbonation was employed to pretreat steel slag supplementary cementitious materials (SCMs) to improve its hydration reactivity and volume stability. The microstructures of carbonated steel slag SCMs and their impact on the hydration, soundness and compressive strengths of cement materials were investigated. Results indicated that nano-CaCO3 and amorphous SiO2 gel were the main carbonation products of steel slag, which constructed a porous microstructure, leading to an obvious increase in specific surface area by 77.11%. The nano-CaCO3 and amorphous SiO2 were involved in cement hydration to form monocarboaluminate and C-S-H respectively, which increased the hydration degree, enhanced the interface between the steel slag and hydrated cement matrix. For instance, compressive strength of cement paste mixed with 30 wt% carbonated steel slag was increased by 9.7 % compared with that of the paste incorporating noncarbonated steel slag. The autoclave expansion of cement paste containing 30 wt% carbonated steel slag was 0.17% whereas that of the paste containing uncarbonated steel slag was disintegrated as a result of excessive expansion. This study provides a novel way to utilize the steel slag to prepare high quality SCMs for being used as a replacement of cement.

Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur?

Current carbon cycle models attribute rising atmospheric CO2 as the major driver of the increased terrestrial carbon sink, but with substantial uncertainties. The photosynthetic response of trees to elevated atmospheric CO2 is a necessary step, but not the only one, for sustaining the terrestrial carbon uptake, but can vary diurnally, seasonally and with duration of CO2 exposure. Hence, we sought to quantify the photosynthetic response of the canopy-dominant species, Quercus robur, in a mature deciduous forest to elevated CO2 (eCO2) (+150 μmol mol−1 CO2) over the first 3 years of a long-term free air CO2 enrichment facility at the Birmingham Institute of Forest Research in central England (BIFoR FACE). Over 3000 measurements of leaf gas exchange and related biochemical parameters were conducted in the upper canopy to assess the diurnal and seasonal responses of photosynthesis during the 2nd and 3rd year of eCO2 exposure. Measurements of photosynthetic capacity via biochemical parameters, derived from CO2 response curves, (Vcmax and Jmax) together with leaf nitrogen concentrations from the pre-treatment year to the 3rd year of eCO2 exposure, were examined. We hypothesized an initial enhancement in light-saturated net photosynthetic rates (Asat) with CO2 enrichment of ≈37% based on theory but also expected photosynthetic capacity would fall over the duration of the study. Over the 3-year period, Asat of upper-canopy leaves was 33 ± 8% higher (mean and standard error) in trees grown in eCO2 compared with ambient CO2 (aCO2), and photosynthetic enhancement decreased with decreasing light. There were no significant effects of CO2 treatment on Vcmax or Jmax, nor leaf nitrogen. Our results suggest that mature Q. robur may exhibit a sustained, positive response to eCO2 without photosynthetic downregulation, suggesting that, with adequate nutrients, there will be sustained enhancement in C assimilated by these mature trees. Further research will be required to understand the location and role of the additionally assimilated carbon.

Mechanisms of shale water wettability alteration with chemical groups after CO2 injection: Implication for shale gas recovery and CO2 geo-storage

Supercritical carbon dioxide (Sc-CO2) has been used in shale gas exploitation for efficient fracturing and the added benefit of CO2 geo-storage. Many studies have suggested that the water wettability of shale significantly influences the success of shale gas recovery. The aim of this work was to investigate the effect of CO2 treatment on shale water wettability. X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to analyze the raw and CO2-treated shale samples using peak fitting and grey relational (GR) analyses. The results showed that the CO2-treated shale surface showed weaker hydrophilicity than the raw shale sample. The GR analysis results indicated that Si–OH contributed most to shale water wettability because Si–OH formed hydroxyl bonds with the water molecules on the shale surface, significantly enhancing shale hydrophilicity. The proportion of Si–OH in the shale chemical groups decreased, and fewer hydroxyl bonds were formed after the CO2 treatment, weakening shale hydrophilicity. The content of hydrophilic –OH groups was lower in the CO2-treated shale samples than the raw samples, and increases and decrease were observed in the content of the C–O groups. A decrease in the contents of hydrophilic calcite, dolomite, and clay minerals also contributed to shale hydrophilicity weakening. These results imply that the injection of CO2 into shale reservoirs weakens shale hydrophilicity, improving shale gas recovery because the water blocking effect is minimized. The findings in this research can be used for shale wettability reversal by chemical reagents, which is of great significance for improving gas productivity and CO2 geological storage.

무 싹채소 탄산 가스 처리에 따른 생육과 수확후 품질 특성 비교

As sprout vegetables of interest growing, its maintaining the quality of the technology was needed to solve the problem of increasing growth and maintain quality after harvest. This experiment proved that the quality of radish sprout vegetable was affected by CO2 treatment during cultivation. Thus, the effect of CO2 treatment during cultivation on postharvest quality of radish sprout vegetable was investigated in terms of the quality changes in weight loss, gas partial pressure, SPAD, hue angle external appearance during storage at polypropylene film (thickness 30 μm) at 10oC. CO2 treatment used the way to gas with 700 ppm or carbonated water with 700 ppm and 1,400 ppm. The study revealed that growths on CO2 treated plant were more than those of non-treatment on stem length. After harvesting, the CO2 treated plant and control growing little different characteristics on fresh weight, plant length and so on. However, there were no differences between the CO2 treated plant and control on the Fv/Fm and SOD (superoxide dismutase). In gas partial pressure, the O2 consumption and CO2 accumulation of the CO2 treated plant tended to be more than that of non-treated plant. This study also checked that after packaging, the effects of CO2 treatment during cultivation on the quality of radish sprout vegetable was not significant. However, there were tended to CO2 treatments were lower value compared to control on SPAD, hue angle and general appearance. CO2 treatments of radish sprouting vegetable before harvest were improve growth of stem length, but ones were not improving the maintain of quality on radish sprout vegetable during shelf-life period. The results indicated that CO2 treatment only affected stem elongation until radish sprout vegetable its growth.

Effects of carbon dioxide on turkey poult performance and behavior.

Appropriate ventilation of poultry facilities is critical for achieving optimum performance. Ventilation promotes good air exchange to remove harmful gases, excessive heat, moisture, and particulate matter. In a turkey brooder barn, carbon dioxide (CO2) may be present at higher levels during the winter due to reduced ventilation rates to maintain high temperatures. This higher CO2 may negatively affect turkey poult performance. Therefore, the objective of this study was to evaluate the effects of subjecting tom turkey poults (commercial Large White Hybrid Converters) to different constant levels of atmospheric CO2 on their growth performance and behavior. In three consecutive replicate trials, a total of 552 poults were weighed post-hatch and randomly placed in 3 environmental control chambers, with 60 (Trial 1) and 62 (Trials 2 and 3) poults housed per chamber. They were reared with standard temperature and humidity levels for 3 wks. The poults were exposed to 3 different fixed CO2 concentrations of 2,000, 4,000, and 6,000 ppm throughout each trial. Following each trial (replicate), the CO2 treatments were switched and assigned to a different chamber in order to expose each treatment to each chamber. At the end of each trial, all poults were sent to a local turkey producer to finish growout. For each trial, individual body weight and group feed intake were measured, and mortality and behavioral movement were recorded. Wk 3 and cumulative body weight gain of poults housed at 2,000 ppm CO2 was greater (P < 0.05) than those exposed to 4,000 and 6,000 ppm CO2. Feed intake and feed conversion were unaffected by the different CO2 concentrations. No significant difference in poult mortality was found between treatments. In addition, no effect of CO2 treatments was evident in the incidence of spontaneous turkey cardiomyopathy for turkeys processed at 19 wk of age. Poults housed at the lower CO2 level (2,000 ppm) demonstrated reduced movement compared with those exposed to the 2 higher CO2 concentrations.

Impact of high CO2 levels on heat shock proteins during postharvest storage of table grapes at low temperature. Functional in vitro characterization of VVIHSP18.1

The role played by heat shock proteins (HSPs) in improving fruit quality during postharvest treatments has mainly been studied regarding heat treatments, while little is known about the effect of CO2 treatments. In this study, we have analyzed the gene expression of five heat shock proteins (HSPs) and one heat shock factor (HSF) in the skin of red table grapes (Vitis vinifera cv. Cardinal) to determine whether a pretreatment with high CO2 levels (20 kPa) modulated their expression and how the length of the treatment (1 or 3 d) could influence this change. The 3-d high CO2-treatment was effective in reducing total decay and induced the accumulation of three small HSPs (VviHSP18.1, VviHSP18.2 and VviHSP22.0), whereas VviHSP70.0 and VviHSF4-a gene expression were induced by both treatments. To shed light on the putative physiological role of a small HSP (VviHSP18.1) acting as a chaperone, the recombinant protein was overexpressed in Escherichia coli. It was then purified and mass spectrometry confirmed that the isolated protein was VviHSP18.1, belonging to class I sHSP. Although the purified protein was stable at different high temperatures, when temperature was above 70 °C, a weaker and smaller protein band appeared which was identified by mass spectrometry as VviHSP18.1 with a C-terminal truncation. The recombinant VviHSP18.1 protein displayed chaperone activity which protects citrate synthase (CS) and malate dehydrogenase (MDH) from thermal aggregation at 45 °C, and also displayed the protection of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) activities at 55 °C and 65 °C, respectively. By contrast, VviHSP18.1 did not protect LDH from freezing-induced inactivation. Taken together, these results support the hypothesis that a high CO2 treatment is an active process where HSPs could participate in preventing the denaturation and dysfunction of different proteins.

Effect of atmospheric carbon dioxide concentration on the cultivation of bovine Mycoplasma species

Recommendations for bovine mycoplasma culture CO2 concentrations are varied and were not empirically derived. The objective of this study was to determine whether the growth measures of bovine mycoplasma isolates differed when incubated in CO2 concentrations of 10 or 5% or in candle jars (2.7 ± 0.2% CO2). Growth of Mycoplasma bovis (n = 22), Mycoplasma californicum (n = 18), and other Mycoplasma spp. (n = 10) laboratory isolates was evaluated. Isolate suspensions were standardized to approximately 108 cfu/mL and serially diluted in pasteurized whole milk to achieve test suspensions of 102 and 106 cfu/mL. One hundred microliters of each test dilution was spread in duplicate onto the surface of a modified Hayflick's agar plate. Colony growth was enumerated on d 3, 5, and 7 of incubation. A mixed linear model included the fixed effects of CO2 treatment (2.7, 5, or 10%), species, day (3, 5, or 7), and their interactions, with total colony counts as the dependent variable. Carbon dioxide concentration did not significantly affect overall mycoplasma growth differences, but differences between species and day were present. Colony counts (log10 cfu/mL) of M. bovis were 2.6- and 1.6-fold greater than M. californicum and other Mycoplasma spp., respectively. Growth at 7 d of incubation was greater than d 3 and 5 for all species. These findings were confirmed using field isolates (n = 98) from a commercial veterinary diagnostic laboratory. Binary growth responses (yes/no) of the field isolates were not different between CO2 treatments but did differ between species and day of incubation. On average, 57% of all field isolates were detected by 3 d of incubation compared with 93% on d 7. These results suggest that the range of suitable CO2 culture conditions and incubation times for the common mastitis-causing Mycoplasma spp. may be broader than currently recommended.

Long-term exposure to elevated carbon dioxide does not alter activity levels of a coral reef fish in response to predator chemical cues

Levels of dissolved carbon dioxide (CO2) projected to occur in the world’s oceans in the near future have been reported to increase swimming activity and impair predator recognition in coral reef fishes. These behavioral alterations would be expected to have dramatic effects on survival and community dynamics in marine ecosystems in the future. To investigate the universality and replicability of these observations, we used juvenile spiny chromis damselfish (Acanthochromis polyacanthus) to examine the effects of long-term CO2 exposure on routine activity and the behavioral response to the chemical cues of a predator (Cephalopholis urodeta). Commencing at ~3–20 days post-hatch, juvenile damselfish were exposed to present-day CO2 levels (~420 μatm) or to levels forecasted for the year 2100 (~1000 μatm) for 3 months of their development. Thereafter, we assessed routine activity before and after injections of seawater (sham injection, control) or seawater-containing predator chemical cues. There was no effect of CO2 treatment on routine activity levels before or after the injections. All fish decreased their swimming activity following the predator cue injection but not following the sham injection, regardless of CO2 treatment. Our results corroborate findings from a growing number of studies reporting limited or no behavioral responses of fishes to elevated CO2.Significance statementAlarmingly, it has been reported that levels of dissolved carbon dioxide (CO2) forecasted for the year 2100 cause coral reef fishes to be attracted to the chemical cues of predators. However, most studies have exposed the fish to CO2 for very short periods before behavioral testing. Using long-term acclimation to elevated CO2 and automated tracking software, we found that fish exposed to elevated CO2 showed the same behavioral patterns as control fish exposed to present-day CO2 levels. Specifically, activity levels were the same between groups, and fish acclimated to elevated CO2 decreased their swimming activity to the same degree as control fish when presented with cues from a predator. These findings indicate that behavioral impacts of elevated CO2 levels are not universal in coral reef fishes.

Angiotensin-converting Enzyme Inhibition Improves the Effectiveness of Transcutaneous Carbon Dioxide Treatment.

To study the effect of carbon dioxide (CO2) therapy on the nitric oxide (NO) pathway by monitoring plasma asymmetric dimethylarginine (ADMA) concentrations. Forty-seven hypertensive patients who underwent transcutaneous CO2 therapy were enrolled. Thirty healthy individuals were recruited for the control group. Blood samples were taken one hour before, as well as one hour, 24 hours and 3 weeks after the first CO2 treatment. Controls did not undergo CO2 treatment. Plasma ADMA levels were measured by ELISA. ADMA levels decreased significantly one hour after the first CO2 treatment compared to the baseline concentrations (p=0.003). Significantly greater reduction was found among patients in whom angiotensin converting enzyme inhibitors (ACEIs) were administered (p=0.019). The short- and long-term decrease of ADMA levels suggests that CO2 is not only a vasodilator, but also has a beneficial effect on the NO pathway. ACE inhibition seems to enhance the effect of CO2 treatment.

Contrasting effects of ocean acidification on reproduction in reef fishes

Differences in the sensitivity of marine species to ocean acidification will influence the structure of marine communities in the future. Reproduction is critical for individual and population success, yet is energetically expensive and could be adversely affected by rising CO2 levels in the ocean. We investigated the effects of projected future CO2 levels on reproductive output of two species of coral reef damselfish, Amphiprion percula and Acanthochromis polyacanthus. Adult breeding pairs were maintained at current-day control (446 μatm), moderate (652 μatm) or high CO2 (912 μatm) for a 9-month period that included the summer breeding season. The elevated CO2 treatments were consistent with CO2 levels projected by 2100 under moderate (RCP6) and high (RCP8) emission scenarios. Reproductive output increased in A. percula, with 45–75 % more egg clutches produced and a 47–56 % increase in the number of eggs per clutch in the two elevated CO2 treatments. In contrast, reproductive output decreased at high CO2 in Ac. polyacanthus, with approximately one-third as many clutches produced compared with controls. Egg survival was not affected by CO2 for A. percula, but was greater in elevated CO2 for Ac. polyacanthus. Hatching success was also greater for Ac. polyacanthus at elevated CO2, but there was no effect of CO2 treatments on offspring size. Despite the variation in reproductive output, body condition of adults did not differ between control and CO2 treatments in either species. Our results demonstrate different effects of high CO2 on fish reproduction, even among species within the same family. A greater understanding of the variation in effects of ocean acidification on reproductive performance is required to predict the consequences for future populations of marine organisms.

Juvenile Atlantic cod behavior appears robust to near-future CO2 levels.

BackgroundOcean acidification caused by the anthropogenic release of CO2 is considered a major threat to marine ecosystems. One unexpected impact of elevated water CO2 levels is that behavioral alterations may occur in tropical reef fish and certain temperate fish species. These effects appear to alter many different types of sensory and cognitive functions; if widespread and persistent, they have the potential to cause ecosystem changes.MethodsWe investigated whether economically and ecologically important Atlantic cod also display behavioral abnormalities by exposing 52 juvenile cod to control conditions (500 μatm, duplicate tanks) or an end-of-the-century ocean acidification scenario (1000 μatm, duplicate tanks) for one month, during which time the fish were examined for a range of behaviors that have been reported to be affected by elevated CO2 in other fish. The behaviors were swimming activity, as measured by number of lines crossed per minute, the emergence from shelter, determined by how long it took the fish to exit a shelter after a disturbance, relative lateralization (a measure of behavioral turning side preference), and absolute lateralization (the strength of behavioral symmetry).ResultsWe found no effect of CO2 treatment on any of the four behaviors tested: activity (F = 1.61, p = 0.33), emergence from shelter (F = 0.13, p = 0.76), relative lateralization (F = 2.82, p = 0.50), and absolute lateralization (F = 0.80, p = 0.26).ConclusionOur results indicate that the behavior of Atlantic cod could be resilient to the impacts of near-future levels of water CO2.

Resiliency of juvenile walleye pollock to projected levels of ocean acidification

As atmospheric concentrations of CO2 rise, the pH of high-latitude oceans is pre- dicted to decrease by 0.3 to 0.5 units by 2100. Several biological consequences of ocean acidifica- tion across this pH range have already been documented in invertebrates and tropical marine fishes. However, little work has been done examining potential responses of the temperate and boreal marine fish species that support major fisheries. In 2 experiments, we examined the growth responses of juvenile walleye pollock Theragra chalcogramma at ambient and 3 elevated CO2 lev- els. In a short-term experiment with yearlings, CO2 treatment had no significant effect on growth or condition after 6 wk of rearing. Elevated CO2 levels (>450 µatm) increased the rate of otolith deposition, but did not affect otolith elemental composition. In a second experiment, growth in length of sub-yearlings over 12 wk at 8°C was 7.2% faster in the 2 higher CO2 treatments (>1200 µatm) than in the lower CO2 treatments (<900 µatm). Growth of sub-yearlings measured during 11 subsequent weeks of rearing at 2.5°C did not differ among CO2 treatments. There was no effect of CO2 treatment on condition factor following either phase of the experiment. Sub- yearling consumption rates were not directly affected by CO2 treatment, confirming that growth at elevated CO2 levels is not maintained through compensatory feeding. While not exhaustive of potential interactive environmental factors, these experiments demonstrate a general resiliency of growth energetics in juvenile walleye pollock to the direct effects of CO2 changes predicted for the Gulf of Alaska and Bering Sea in the next century.

Transitory effects of elevated atmospheric CO2 on fine root dynamics in an arid ecosystem do not increase long‐term soil carbon input from fine root litter

Experimental increases in atmospheric CO₂ often increase root production over time, potentially increasing soil carbon (C) sequestration. Effects of elevated atmospheric CO₂ on fine root dynamics in a Mojave desert ecosystem were examined for the last 4.5 yr of a long-term (10-yr) free air CO₂ enrichment (FACE) study at the Nevada desert FACE facility (NDFF). Sets of minirhizotron tubes were installed at the beginning of the NDFF experiment to characterize rooting dynamics of the dominant shrub Larrea tridentata, the codominant shrub Ambrosia dumosa and the plant community as a whole. Although significant treatment effects occurred sporadically for some fine root measurements, differences were transitory and often in opposite directions during other time-periods. Nonetheless, earlier root growth under elevated CO₂ helped sustain increased assimilation and shoot growth. Overall CO₂ treatment effects on fine root standing crop, production, loss, turnover, persistence and depth distribution were not significant for all sampling locations. These results were similar to those that occurred near the beginning of the NDFF experiment but unlike those in other ecosystems. Thus, increased C input into soils is unlikely to occur from fine root litter under elevated atmospheric CO₂ in this arid ecosystem.