Long-term CO2 Research Articles

Review of energy modelling, energy efficiency models improvement and carbon dioxide emissions mitigation options for the cement industry in South Africa

The cement sector in South Africa contributes approximately 1 % to the South African national greenhouse gas inventory. In line with the country’s GDP increasing which will cause population to increase, the demand for housing, public and private structural infrastructures continues to increase. It is assumed that the demand for cement will also increase proportionally as well as its associated CO2 emission. The purpose of this study is to firstly; review previous energy modelling strategies in South Africa and specifically in the cement industry if any in order to examine the alignment of the cement industry’s strategies with that of the South African government since becoming part of the Paris agreement signatories. Previous studies of energy efficiency, modelling, and GHG emissions were analyzed and reviewed for the understanding of the readiness of South Africa’s cement industry to tackle her energy and global warming issues. South Africa is in a position to tackle the energy efficiency and GHG emissions problem through redesigning and consolidated critical data collection will, driven by the government and responsible stakeholders. Secondly; if any previous strategies are in place but in isolation, to examine the potential for long-term energy efficiency strategies and CO2 mitigation options for the cement sector in South Africa; as these two elements have a distinguishable link. Cement production is an energy-intensive process that consists of combustion-and process-related emissions. This study will employ-two modelling frameworks to examine strategies for reducing cement sector energy demand and associated CO2 emission for the period 2015 to 2050 (35 years) with 5-year intervals parallel to the Paris agreement. After reviewing energy models, the study will employ the low emissions analysis platform (LEAP) to model possible energy saving methods in the combustion process and other forms of energy supply in the context of South African cement sector. The existing reviewed methods and results will be compared and the LEAP will provide a second set of comparable results in order to influence policy and inform decision-making. For process-related emissions in the sector, the study will develop an excel-based model to examine possible strategies for reducing CO2 emission in the sector. The results will be examined in terms of cumulative energy savings, GHG emissions, and marginal abatement cost of carbon.

In situregeneration of copper catalysts for long-term electrochemical CO2reduction to multiple carbon products

We report anin situcatalyst regeneration strategy that can extend the operation time of Cu-based catalysts for electrochemical CO2reduction many times.

Short-Term and Long-Term Effects of Natural and Artificial Carbonaceous Substrates on Greenhouse Gas Fluxes

The emissions of two greenhouse gases (GHG), carbon dioxide (CO2) and nitrous oxide (N2O), from six substrates with different carbonaceous content were compared in short and long-term incubation experiments. Three natural soils and three artificial chars were mixed with carbon (C) poor soil (Cambisol) to simulate real conditions after application of char to farmland. The natural soils were a Cambisol, an Anthrosol and a Histosol with C contents of 1.3%, 4.4% and 13.2%, respectively. The three chars produced through thermal conversion of wood chips by hydrothermal carbonisation (HTC), fluidized bed gasification and pyrolysis had C contents of 56.9%, 75.4% and 79.9%, respectively. Emission rates of CO2 and N2O from the rewetted substrates were measured by gas chromatography over a short time of 72 h and over a long period of nearly two years. The short-term CO2 emissions from the natural soils showed a clear relationship to their C content. The emission rate for the Histosol/Cambisol mixture was three times higher than that for the pure Cambisol, 77.1 vs. 23.5 mg CO2-C kg−1 organic matter (OM) per hour. The C emission rates for the char/Cambisol mixtures were much lower, ranging between 3.0 and 9.1 mg CO2-C kg OM−1 h−1 , and did not correspond to their total C contents. Comparison between the two incubation lengths showed that the long-term CO2 emission rates were generally one order of magnitude lower than the short-term rates. The final emission rates for natural substrates over a period of two years were still twice those for artificial char substrates, between 2.2–3.5 mg CO2-C kg OM−1 h−1 and 1.3–1.8 mg CO2-C kg OM−1 h−1 , respectively. Although the contents of total nitrogen (Ntot) and extractable nitrogen (Nmin) were considerable in the chars under study, enhanced N2O release was not observed in the incubation experiments. Instead, N2O emission rates in the three mixtures of chars and Cambisol were lower by one to two orders of magnitude compared to the pure Cambisol in short-term incubations. Even long-term N2O emissions were 5 to 9 times lower. The highest degree of N2O reduction was found for the HTC char. Because of the high global warming potential of N2O, this positive effect of chars may play an important role in mitigating emissions of CO2 equivalents. Both CO2 and N2O must be taken into account when balancing GHG emitted after chars (biochar, gasifier char, HTC char) are applied to soil.

China actively promotes CO2 capture, utilization and storage research to achieve carbon peak and carbon neutrality

China actively promotes CO2 capture, utilization and storage research to achieve carbon peak and carbon neutrality

Influence of long-term CH4 and CO2 treatment on the pore structure and mechanical strength characteristics of Baijiao coal

In order to study the influence of adsorptive gas on coal pore structures and mechanical strength, coal specimens were placed in a low-pressure environment of CH4 or CO2 for 30 days to ensure that the specimens were saturated and fully interacted with the gas. Low-pressure nitrogen adsorption, scanning electron microscope, X-ray diffraction, and uniaxial compressive strength tests were employed to study coal's microstructure change and strength characteristics. The results show that after CH4 or CO2 treatment, the proportion of macropores increases by 38.87% and 22.89%, and that of mesopores decrease by 6.34% and 3.73%, respectively, which indicates the evolution of mesopores to macropores. The microcrystalline structure parameters change obviously after long-term gas adsorption treatment. The values of d002 and d100 increase, while Lc, La, and Mc's values both decrease, resulting in a loose coal structure. Besides, a conceptual model is proposed to explain the evolution mechanism of pore structures under the effect of long-term gas adsorption.

Study on long-term variation characteristics of indoor CO2 concentrations based on a data-driven method

People sometimes stay indoors for a long time, such as sleepiness at night in bedrooms, study indoors with doors and windows closed, and it is significant to study long-term variation characteristics of indoor carbon dioxide (CO2) concentrations for studying the effects of the CO2 concentrations and improving indoor air quality. However, the researches on the variation of the indoor CO2 concentrations and its effects on humans were mainly focused on short-term time (≤2h) caused by some problems, such as physiological needs of subjects (for example, bathroom breaks) and insufficient financial resources for long-term measurements. To overcome these problems, a data-driven CO2 model was proposed to analyze the long-term (≥8h) variation characteristics of the indoor CO2 concentrations, in which only short-term data need to be measured. The CO2 concentrations of this study was measured within 1 h under different ventilation conditions in a 30 m3 experiment cabin. The measured data of some conditions were used to calibrate the key parameters of the data-driven CO2 model, such as indoor CO2 release rate and natural ventilation rate, and other data were used to validate the accuracy of the data-driven CO2 model under mechanical and natural ventilation conditions. And then the long-term CO2 concentration variations and their stability values were obtained and analyzed under the different ventilation conditions. Results indicate that the simulation errors of the model in mechanical and natural ventilation conditions were less than 3%. The indoor CO2 concentrations will reach 1000 ppm and 5000 ppm in about 0.5 h and 5.9 h under natural ventilation conditions, respectively. And a ventilation rate of 30 m3/h per person can ensure the indoor CO2 concentrations complying with the criteria of less than 1000 ppm. Therefore, the research methods and results of this study can provide references and suggestions for the studies about CO2 concentration variations and influences, and then to improve the indoor air quality.

On the application of silica gel for mitigating CO2 leakage in CCS projects: Rheological properties and chemical stability

Silica sol gels have the potential to act as sealing agents to reduce leakage risks associated with long-term CO 2 storage. This study considers the effects of brines of varying chemical composition on the formation of sol gels, their viscosity, and their long term stability. The gelation times of sol–gel solutions were measured for different concentrations of SiO 2 , Na + , K + , Ca 2＋ , and Mg 2 + as well as pH levels. Individually, increased concentrations of SiO 2 , Na + , K + , Ca 2＋ , and Mg 2 + reduced gelation time. However, the combined effects of Na + , HCl, and Ca 2＋ or Mg 2 + were found to delay gelation, compared to when only Ca 2＋ or Mg 2 + is added. Gelation times were similarly found to be a complex function of the pH of the system. Empirical fits were obtained describing the gelation times and the precursor sol viscosities from the start of activation until gelation. Expressions are presented that relate the changes in the fitting parameters in response to variations in gel composition. There is good agreement between the experimental measurements and the models, which could be used to predict gelation rates in field-scale applications. The durability of the gel was also investigated through experiments in which the gels were exposed to different solutions of varying salinity and pH. These results showed that silica gels were stable after 45 days of brine exposure, with the most significant change being a slight expansion of the gel. Additional experiments revealed that the gels remained thermally stable for expended periods at a temperature of 60 °C. • Gelation was monitored in silca sol solutions of varying composition. • Gels were also exposed to saline and acidic brines for extended periods. • Robust empirical models were developed for gelation time and dynamic viscosity. • Silica gels were chemically stable over a wide range of salinity and pH.

Moisture-tolerant diamine-appended metal–organic framework composites for effective indoor CO2 capture through facile spray coating

Reducing the concentration of indoor carbon dioxide (CO2) to an acceptable safe level of 1,000 ppm is an important issue because a high level of CO2 in closed spaces causes lethargy and fatigue. Although diamine-functionalized metal–organic framework (MOF) adsorbents with high CO2 capacities under indoor air conditions are available, the moisture-induced degradation of MOFs and their shaping remains a challenge for practical applications. Herein, we report the fabrication of epn-functionalized Mg2(dobpdc) composites, which proceeded by mixing with a polystyrene-block-polybutadiene-block-polystyrene (SBS) hydrophobic polymer (epn = 1-ethylpropane-1,3-diamine; dobpdc4− = 4,4′-dioxido-3,3′-biphenyldicarboxylate). The composites were successfully shaped in the form of membranes with different amounts of MOF (epn-MOFX@SBS; X = 60–80 wt%). Specifically, epn-MOF80@SBS exhibited a significant CO2 adsorption of 2.8 mmol g−1 at 1,000 ppm with recyclable working capacity. The composites were further coated on the surfaces of different supports, such as a Ti mesh, an air filter, and granular activated carbon via a facile and simple spraying method. The experimental conditions were 1,000 ppm CO2 and 60% relative humidity in a 50-L chamber; the coated materials displayed invariant CO2 removal performances over 10 cycles and even after 7 days of exposure. The recyclable and long-term CO2 adsorption capacities demonstrate that the MOF-polymer composites and their coating on various supports provide a useful and effective route for indoor CO2 capture under realistic conditions.

Mxene coupled over nitrogen-doped graphene anchoring palladium nanocrystals as an advanced electrocatalyst for the ethanol electrooxidation

Development of good support materials is widely adopted as a valid strategy to fabricate high performance electrocatalysts for the ethanol oxidation reaction (EOR). In this study, the small diameter Ti3C2Tx MXene thin nanosheets inserted into three-dimensional nitrogen-doped grapheme (NG) was constructed via a facile hydrothermal method and employed as support materials for anchoring Pd nanocrystals (Pd/Ti3C2Tx@NG). The obtained-Pd/Ti3C2Tx@NG as EOR electrocatalyst in alkaline media outperforms the commercial Pd/C with better electrocatalytic activity, enhanced long-term stability and high CO tolerance. The Ti3C2Tx inserted into NG probably plays a key role for enhancing the properties of the synthesized-catalyst. Inserting Ti3C2Tx into NG allows the electrocatalysts to have high porosity, surface hydrophilicity, sufficient number of anchor sites for Pd nanocrystals and modifies its electronic properties, which can promote the electrocatalytic activity and durability. The enhanced EOR performance endows Pd/Ti3C2Tx@NG with great application potential in fuel cells as an anode catalyst. Furthermore, the prepared Ti3C2Tx@NG is also suitable in various desired applications, especially other oxidation reactions.

Sustainable long-term energy planning for a district in Suzhou City, China

A city district in Suzhou aims to develop a progressive, long-term sustainable energy strategy. This study examines possible energy planning pathways for the district through the development of a long-term optimization model and a range of energy scenarios until 2050. The scenarios explore different CO2 emission reduction strategies and technology mixes/parameters. Results suggest which low-carbon energy conversion technologies and efficiency measures should be adopted by the district alongside supportive local policies and targets. Photovoltaic (PV) and waste energy converters are two renewable energy technologies which are taken up at maximum possible rates in the evaluated scenarios to reduce long-term CO2 emissions. Once local renewable resources are exhausted, natural gas-based combined-cycle plants (CCP) and combined heat and power plants (CHP) are required to further reduce emissions, alongside efficiency measures in the built environment. Carbon capture and storage (CCS) technologies also demonstrate the potential to drastically reduce emissions; however, local feasibility studies are needed to support their implementation. Study results prescribe renewable energy share and CO2 emission reduction targets until 2050 for the district. Appropriate local policy and planning targets should also be accompanied by supplementary support studies, including local feasibility, renewable energy resource, and demand-side management studies.

No evidence for global decrease in CO2 concentration during the first wave of COVID-19 pandemic.

Numerous studies have reported that CO2 emissions have decreased because of global lockdown during the first wave of the COVID-19 pandemic. However, previous estimates of the global CO2 concentration before and after the outbreak of the COVID-19 pandemic are limited because they are based on energy consumption statistics or local specific in-situ observations. The aim of the study was to explore objective evidence for various previous studies that have claimed the global CO2 concentration decreased during the first wave of the COVID-19 pandemic. There are two ways to measure the global CO2 concentration: from the top-down using satellites and the bottom-up using ground stations. We implemented the time-series analysis by comparing the before and after the inflection point (first wave of COVID-19) with the long-term CO2 concentration data obtained from World Meteorological Organization Global Atmosphere Watch (WMO GAW) and Greenhouse Gases Observing Satellite (GOSAT). Measurements from the GOSAT and GAW global monitoring stations show that the CO2 concentrations in Europe, China, and the USA have continuously risen in March and April 2020 compared with the same months in 2019. These data confirm that the global lockdown during the first wave of the COVID-19 pandemic did not change the vertical CO2 profile at the global level from the ground surface to the upper layer of the atmosphere. The results of this study provide an important foundation for the international community to explore policy directions to mitigate climate change in the upcoming post-COVID-19 period.

Quantitatively determine CO2 geosequestration capacity in depleted shale reservoir: A model considering viscous flow, diffusion, and adsorption

Depleted hydrocarbon reservoirs have been gradually recognized as the potential candidates for geological storage of carbon dioxide due to their wide geographical spread and large storage capacity. Reliably assess CO2 geosequestration capacity (CGC) of depleted hydrocarbon reservoirs lays the foundation of CO2 long-term geosequestration security. In this study, a model, considering CO2 viscous flow, diffusion, and adsorption in shale reservoirs, is established to determine bottom-hole pressure during CO2 injection through a hydraulic fractured multiwell-pad. The computational efficient semi-analytical solution is obtained by superposition principle and Laplace numerical inverse technique. Applying the developed model, a workflow is accordingly proposed to evaluate CGC of depleted shale reservoirs. As a case verification, the calculation on the CGC of a depleted shale reservoir from Barnett Shale in Texas is conducted, which illustrates that its CGC reaches up to 3.8 × 1012m3 when the constrained injection pressure (CIP) is high. Moreover, sensitivity analyses suggest that most reservoir parameters exhibit ignorable impacts on CGC when CIP is low whereas their effects on CGC are significant at high CIP. For instance, for the low-CIP, CGC just increases by approximately 6.7% when adsorption index increases from 2.5 to 250. As for the high-CIP scenario, CGC significantly increases 164 times for the same adsorption index range. In contrast to reservoir parameters, engineering parameters generally show great impacts on CGC at low CIP whereas their effects on CGC are negligible when CIP is high. To be more specific, CGC increases by 2.42 times when injection rate ratio of two wells ranges from 8 to 0.5 under low-CIP condition whereas CGC increases just by 0.47 times when CIP is high. The findings obtained in this study pave the way for the long-term CO2 geosequestration in depleted hydrocarbon reservoirs with much less efforts.

Lipid Remodeling Reveals the Adaptations of a Marine Diatom to Ocean Acidification.

Ocean acidification is recognized as a major anthropogenic perturbation of the modern ocean. While extensive studies have been carried out to explore the short-term physiological responses of phytoplankton to ocean acidification, little is known about their lipidomic responses after a long-term ocean acidification adaptation. Here we perform the lipidomic analysis of a marine diatom Phaeodactylum tricornutum following long-term (∼400 days) selection to ocean acidification conditions. We identified a total of 476 lipid metabolites in long-term high CO2 (i.e., ocean acidification condition) and low CO2 (i.e., ambient condition) selected P. tricornutum cells. Our results further show that long-term high CO2 selection triggered substantial changes in lipid metabolites by down- and up-regulating 33 and 42 lipid metabolites. While monogalactosyldiacylglycerol (MGDG) was significantly down-regulated in the long-term high CO2 selected conditions, the majority (∼80%) of phosphatidylglycerol (PG) was up-regulated. The tightly coupled regulations (positively or negatively correlated) of significantly regulated lipid metabolites suggest that the lipid remodeling is an organismal adaptation strategy of marine diatoms to ongoing ocean acidification. Since the composition and content of lipids are crucial for marine food quality, and these changes can be transferred to high trophic levels, our results highlight the importance of determining the long-term adaptation of lipids in marine producers in predicting the ecological consequences of climate change.

Self-regeneration of supported transition metals by a high entropy-driven principle

The sintering of Supported Transition Metal Catalysts (STMCs) is a core issue during high temperature catalysis. Perovskite oxides as host matrix for STMCs are proven to be sintering-resistance, leading to a family of self-regenerative materials. However, none other design principles for self-regenerative catalysts were put forward since 2002, which cannot satisfy diverse catalytic processes. Herein, inspired by the principle of high entropy-stabilized structure, a concept whether entropy driving force could promote the self-regeneration process is proposed. To verify it, a high entropy cubic Zr0.5(NiFeCuMnCo)0.5Ox is constructed as a host model, and interestingly in situ reversible exsolution-dissolution of supported metallic species are observed in multi redox cycles. Notably, in situ exsolved transition metals from high entropy Zr0.5(NiFeCuMnCo)0.5Ox support, whose entropic contribution (TΔSconfig = T⋆12.7 J mol−1 K−1) is predominant in ∆G, affording ultrahigh thermal stability in long-term CO2 hydrogenation (400 °C, >500 h). Current theory may inspire more STWCs with excellent sintering-resistance performance.

Response of Yield, CH4, and N2O Emissions from Paddy Fields to Long-term Elevated CO2 Concentrations

Elevated atmospheric CO2 concentrations([CO2]e) are the main driving force of global climate change, which directly and indirectly affect carbon and nitrogen cycling in the paddy ecosystems. Therefore, understanding the response of rice yield and greenhouse gas emissions to long-term(more than 10 years)[CO2]e from paddy fields is of great significance for food security and future climate change assessment. In this study, strongly and weakly responsive cultivars were used as the experimental materials. Based on a free-air CO2 enrichment(FACE) platform continuously run for 14 years, two treatments of different[CO2] were set:a control(i.e., normal[CO2] and[CO2]a) and a 200 μmol·mol-1 higher than[CO2]a condition, ([CO2]e). CH4 and N2O emissions from the rice paddy fields were monitored in situ by static transparent chamber-gas chromatography, and grain yields were also obtained. The results showed that compared with the[CO2]a treatment, long-term[CO2]e increased grain yields of the strongly and weakly responsive cultivars by 29%-31%(P<0.05) and 12%-14%(P>0.05), and CH4 emissions of the strongly and weakly responsive cultivars were reduced by 21%-59% and 11%-54%, respectively. Furthermore, N2O emissions from the strongly and weakly responsive cultivars were significantly reduced by 70%(P<0.05) and 40%(P<0.05), respectively. The short- and long-term responses of grain yields and CH4 emissions from rice paddy fields to[CO2]e were significantly different. Specifically, with the increase in the duration of[CO2]e, the increases in rice yields and CH4 emissions significantly decreased, while the N2O emissions showed no significant changes. Therefore, under long-term[CO2]e conditions, the strongly responsive cultivar has a high potential to reduce greenhouse gas emission and increase grain yields.

Pegging input prices to output prices—A special price adjustment clause in long-term CO[formula omitted] sales contracts

Oil firms that apply the technique of CO2-enhanced oil recovery inject CO2 into oil reservoirs to increase oil production. The long-term CO2 sales contracts commonly used in the industry often include a special price adjustment clause—the CO2 price is pegged to the oil price faced by the buyer. This is quite different from typical price adjustment clauses in other long-term contracts, which peg the contract price to input costs faced by the supplier. Using a stylized model, we identify plausible conditions under which the pegging practice adopted in the CO2 market is optimal. Numerical simulations calibrated to an active CO2-enhanced oil recovery project suggest that the optimal pegging rate is sensitive to the anticipated oil price level, but not to the oil price variance around that level. The optimal pegging rate is sensitive also to a given oil project’s CO2 “utilization efficiency” – the amount of CO2 required to produce an additional barrel of oil – which is both highly variable across projects and uncertain up front.

Electron-Rich Pincer Ligand-Coupled Cobalt Porphyrin Polymer with Single-Atom Sites for Efficient (Photo)Electrocatalytic CO2 Reduction at Ultralow Overpotential.

Porphyrin and phthalocyanine complexes bearing single-atom catalytic sites (M-N4 ) have been explored as promising electrocatalysts for CO2 reduction reaction (CO2 RR), whose activity can be improved by regulating the ligands and/or the metal centers. Moreover, their photosensitive features also provide the possibility for highly efficient photoelectrocatalytic CO2 RR. Herein, a novel N'NN'-pincer-ligand (N3 )-coupled cobalt porphyrin (CoPor-N3 ) polymer is developed for realizing efficient (photo)electrocatalytic CO2 RR. The unraveled electronic structure and (photo)electrocatalytic features suggest that a synergistic effect between the electron-rich N3 ligands and the Co-N4 single-atom sites in the CoPor-N3 polymer results in the Co centers attaining more electrons, which is beneficial to facilitating the electron transfer to CO2 for the activation and reduction processes. As expected, the resultant CoPor-N3 polymer delivers a good long-term durability and high CO faradaic efficiency (96%) at an ultralow overpotential (0.39V), which outperforms the CoPor alone and most porphyrin-/phthalocyanine-based electrocatalysts reported so far. Moreover, the photosensitivity of CoPor units can further reduce the overpotential to 0.34V with a CO faradaic efficiency over 90% under light illumination. The present findings offer a new approach to constructing porphyrin-based photosensitive electrocatalysts with high-efficiency photoelectrocatalytic CO2 RR.

Detecting the Responses of CO2 Column Abundances to Anthropogenic Emissions from Satellite Observations of GOSAT and OCO-2

The continuing increase in atmospheric CO2 concentration caused by anthropogenic CO2 emissions significantly contributes to climate change driven by global warming. Satellite measurements of long-term CO2 data with global coverage improve our understanding of global carbon cycles. However, the sensitivity of the space-borne measurements to anthropogenic emissions on a regional scale is less explored because of data sparsity in space and time caused by impacts from geophysical factors such as aerosols and clouds. Here, we used global land mapping column averaged dry-air mole fractions of CO2 (XCO2) data (Mapping-XCO2), generated from a spatio-temporal geostatistical method using GOSAT and OCO-2 observations from April 2009 to December 2020, to investigate the responses of XCO2 to anthropogenic emissions at both global and regional scales. Our results show that the long-term trend of global XCO2 growth rate from Mapping-XCO2, which is consistent with that from ground observations, shows interannual variations caused by the El Niño Southern Oscillation (ENSO). The spatial distributions of XCO2 anomalies, derived from removing background from the Mapping-XCO2 data, reveal XCO2 enhancements of about 1.5–3.5 ppm due to anthropogenic emissions and seasonal biomass burning in the wintertime. Furthermore, a clustering analysis applied to seasonal XCO2 clearly reveals the spatial patterns of atmospheric transport and terrestrial biosphere CO2 fluxes, which help better understand and analyze regional XCO2 changes that are associated with atmospheric transport. To quantify regional anomalies of CO2 emissions, we selected three representative urban agglomerations as our study areas, including the Beijing-Tian-Hebei region (BTH), the Yangtze River Delta urban agglomerations (YRD), and the high-density urban areas in the eastern USA (EUSA). The results show that the XCO2 anomalies in winter well capture the several-ppm enhancement due to anthropogenic CO2 emissions. For BTH, YRD, and EUSA, regional positive anomalies of 2.47 ± 0.37 ppm, 2.20 ± 0.36 ppm, and 1.38 ± 0.33 ppm, respectively, can be detected during winter months from 2009 to 2020. These anomalies are slightly higher than model simulations from CarbonTracker-CO2. In addition, we compared the variations in regional XCO2 anomalies and NO2 columns during the lockdown of the COVID-19 pandemic from January to March 2020. Interestingly, the results demonstrate that the variations of XCO2 anomalies have a positive correlation with the decline of NO2 columns during this period. These correlations, moreover, are associated with the features of emitting sources. These results suggest that we can use simultaneously observed NO2, because of its high detectivity and co-emission with CO2, to assist the analysis and verification of CO2 emissions in future studies.

The Impact of Photorespiratory Glycolate Oxidase Activity on Arabidopsis thaliana Leaf Soluble Amino Acid Pool Sizes during Acclimation to Low Atmospheric CO2 Concentrations.

Photorespiration is a metabolic process that removes toxic 2-phosphoglycolate produced by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase. It is essential for plant growth under ambient air, and it can play an important role under stress conditions that reduce CO2 entry into the leaf thus enhancing photorespiration. The aim of the study was to determine the impact of photorespiration on Arabidopsis thaliana leaf amino acid metabolism under low atmospheric CO2 concentrations. To achieve this, wild-type plants and photorespiratory glycolate oxidase (gox) mutants were given either short-term (4 h) or long-term (1 to 8 d) low atmospheric CO2 concentration treatments and leaf amino acid levels were measured and analyzed. Low CO2 treatments rapidly decreased net CO2 assimilation rate and triggered a broad reconfiguration of soluble amino acids. The most significant changes involved photorespiratory Gly and Ser, aromatic and branched-chain amino acids as well as Ala, Asp, Asn, Arg, GABA and homoSer. While the Gly/Ser ratio increased in all Arabidopsis lines between air and low CO2 conditions, low CO2 conditions led to a higher increase in both Gly and Ser contents in gox1 and gox2.2 mutants when compared to wild-type and gox2.1 plants. Results are discussed with respect to potential limiting enzymatic steps with a special emphasis on photorespiratory aminotransferase activities and the complexity of photorespiration.

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.