CO2 Availability Research Articles

Bioprospecting a Natural Antioxidant Peptide for Tomato Biostimulation Under Water Limitations: Physiological Approach

AbstractDrought causes major agricultural losses, threatening food security worldwide. Thus, innovative strategies have been explored to improve crop tolerance to drought. This work focused on one natural peptide (PpT-2) with antioxidant activity, unexplored in plant applications, to evaluate its effectiveness in mitigating drought effect on Solanum lycopersicum L. plants. For that, tomato plants were foliar sprayed with different doses of PpT-2 (0, 15 or 150 mg L−1) and exposed to water Stressed and UnStressed conditions. The plant growth, photosynthesis and oxidative stress-related parameters were evaluated. Plant treatment with PpT-2, mostly at the highest concentration, alleviated diverse effects induced by water restriction: stimulated CO2 assimilation; improved ΦPSII, Fv/Fm and Fv’/Fm’; amended net CO2 assimilation rate and water use efficiency; restricted H2O2 accumulation and lipid peroxidation; stimulated SOD activity. Under UnStressed conditions, PpT-2 induced some degree of stomatal closure, nevertheless without restricting CO2 availability for the non-photochemical processes of photosynthesis, besides of decreasing H2O2 content and CAT activity. Overall, PpT-2 application controlled H2O2 accumulation, and under water limitations improved both photochemical and non-photochemical processes of photosynthesis and promoted drought tolerance, underscoring its potential for managing drought stress in crop species.

Pore accessibility matters in CO2 electrolysis: Preventing H2 formation and boosting triple-phase boundary on microtubular gas-diffusion electrodes

The availability of CO2 near the active sites is crucial for suppressing hydrogen evolution reaction (HER) and improving the kinetics of electrochemical reduction of CO2 (CO2RR) in aqueous electrolytes at high current density. The hollow fiber gas-diffusion electrodes (HFGDEs) configuration can deliver CO2 continuously to catalyst/electrolyte interfaces without requiring a separate gas chamber, contrasting with planar gas-diffusion electrodes (GDEs). However, the relatively inhomogeneous pore geometry on the surface of HFGDEs leads to poor CO2 distribution, resulting in an increasing number of flooded pores and parasitic HER, especially at high current densities. This work presents a facile strategy to enhance CO2 distribution and optimize triple-phase boundary formation by manipulating the surface wettability of HFGDEs. The infiltration and melting of hydrophobic agents (e.g., polytetrafluoroethylene (PTFE)) have been carried out on the Zn nanosheet-deposited Cu hollow fiber. The fluorescent residue area (water surface coverage) with a ∼66.7 % decrease and the observation of CO2 bubbling enhancement confirmed the improvement of CO2 distribution on HFGDE, and the resulting HFGDE achieved around ∼39 % increase in terms of industrial-scale CO partial current density and 4 times higher stability compared to the pristine HFGDE. This research highlights the use of HFGDEs to achieve gas flow-through, further combining with a versatile strategy to enhance CO2 distribution which can be applied for other gas-phase electrolysis reactions through creating improved triple-phase interfaces and maximizing reaction activity.

Comparative techno-economic and carbon footprint analysis of 2,3-butanediol production through aerobic and anaerobic bioconversion of carbon dioxide with green hydrogen

Renewable CO2 and hydrogen have the potential to be the feedstocks of a decarbonized chemical industry, and biochemical conversions offer new alternatives for the industry. There are two options among chemolithotrophic bacteria capable of CO2 fixation: under aerobic conditions, through the use of the Calvin-Benson-Basham cycle, known to produce large-chain compounds, and under anaerobic conditions, through the Wood-Ljungdahl pathway, known to produce short-chain organic molecules. Here, we report a comparison of both bioconversions, made at a simulated industrial scale, considering techno-economic and environmental variables, and using renewable CO2 and H2 as feedstocks. 2,3-butanediol, a mid-range chain compound that can be produced via both routes, was selected for comparison. The comparison was set up in Chile due to expected low-cost renewable hydrogen and renewable CO2 availability. The assessment showed that the minimum selling price of 2,3-butanediol in the anaerobic case was higher (3.91 (USD kg−1)) than in the aerobic case (3.36 (USD kg−1)), with hydrogen being the largest expense in both processes (50 % and 70 % of total expenses respectively). Further, owing to metabolic restrictions, the anaerobic process required almost five times more CO2 than the aerobic process to produce the same amount of 2,3-butanediol. A Monte Carlo analysis showed that in most scenarios the aerobic process was more economically favorable. In environmental terms, the aerobic process had a smaller carbon footprint in all the evaluated scenarios. Therefore, the results suggest that the aerobic process is a more suitable alternative to anaerobic bacteria-based processes for producing 2,3-butanediol from renewable CO2 and hydrogen.

Contrasting species-specific stress response to environmental pH determines the fate of coccolithophores in future oceans

Molecular mechanisms driving species-specific environmental sensitivity in coccolithophores are unclear but crucial in understanding species selection and adaptation to environmental change. This study examined proteomic and physiological changes in three species under varying pH conditions. We showed that changing pH drives intracellular oxidative stress and changes membrane potential. Upregulation in antioxidant, DNA repair and cell cycle-related protein-groups indicated oxidative damage across high (pH 8.8) and low pH (pH 7.6) compared to control pH (pH 8.2), and correlated with reduced growth rates. Upregulation of mitochondrial proteins suggested higher metabolite demand for restoring cellular homeostasis under pH-induced stress. Photosynthetic rates generally correlated with CO2 availability, driving higher net carbon fixation rates at low pH. The intracellular pH-buffering capacity of the coastal Chrysotila carterae and high metabolic adaptability in the bloom-forming Gephyrocapsa huxleyi will likely facilitate their adaptation to ocean acidification or artificial ocean alkalinisation. However, the pH sensitivity of the ancient open-ocean Coccolithus braarudii will possibly result in reduced growth and shrinking of its ecological niche.

Enhanced Production of Microalgal Metabolites Through Aeration Coupled with Stirring

Adequate mixing is a key factor for microalgal cultivation to achieve high biomass production, so it is essential to clarify the comparative effects of different mixing methods on microalgal productivity, which has rarely been studied previously. This work therefore aimed to investigate the effects of different mixing methods (stirring, aeration, and aeration coupled with stirring) on the growth and metabolite composition of Chlorella sorokiniana SDEC-18, a strain with potential for large-scale application. The results showed that mixing was beneficial for carbohydrate accumulation, while dual mixing (aeration coupled with stirring) promoted growth and achieved the highest dry mass and metabolite productivities (including carbohydrates, proteins, and lipids) through enhancement of light energy capture in the entire system. The stirring speed in the dual mixing approach of aeration coupled with stirring was also considered: the optimal condition was found to be 800 rpm. The maximum biomass was 3.56 g L−1, and the carbohydrate productivity was as high as 119.45 mg L−1 d−1, which was the highest metabolite productivity (higher than proteins or lipids), obtained from aeration coupled with stirring at 800 rpm. Our study suggests that aeration coupled with stirring provides a feasible strategy for microalgal production, due to the optimal availability of CO2 and light achieved through effective mixing.

Vertical farming goes dynamic: optimizing resource use efficiency, product quality, and energy costs

Vertical farming is considered to be a key enabler for transforming agrifood systems, especially in or nearby urbanized areas. Vertical farming systems (VFS) are advanced indoor cropping systems that allow for highly intensified and standardized plant production. The close control of environmental parameters makes crop production stable and repeatable, ensuring year-round uniform product quality and quantity irrespective of location. However, due to continuous changes in plant physiology and development, as well as frequent changes in electricity prices, the optimum conditions for crop production and its associated costs can change within days or even minutes. This makes it beneficial to dynamically adjust setpoints for light (intensity, spectrum, pattern, and daylength), CO2, temperature, humidity, air flow, and water and nutrient availability. In this review, we highlight the beneficial effects that dynamic growth conditions can have on key plant processes, including improvements in photosynthetic gas exchange, transpiration, organ growth, development, light interception, flowering, and product quality. Our novel findings based on modeling and experimentation demonstrate that a dynamic daily light intensity pattern that responds to frequent changes in electricity prices can save costs without reducing biomass. Further, we argue that a smart, dynamic VFS climate management requires feedback mechanisms: several mobile and immobile sensors could work in combination to continuously monitor the crop, generating data that feeds into crop growth models, which, in turn, generate climate setpoints. In addition, we posit that breeding for the VFS environment is at a very early stage and highlight traits for breeding for this specialized environment. We envision a continuous feedback loop between dynamic crop management, crop monitoring, and trait selection for genotypes that are specialized for these conditions.

Response to the CO2 concentrating mechanisms and transcriptional time series analysis of Ulva prolifera under inorganic carbon limitation

Ulva prolifera is a dominant species in green tides and has been affecting marine ecosystem for many years. Due to the low availability of CO2 in the environment, U. prolifera utilizes the CO2 concentrating mechanisms (CCMs) to increase intracellular inorganic carbon concentration. However, the transcriptional response mechanism and temporal changes of U. prolifera CCMs based on transcriptomics have not been thoroughly described. Therefore, we induced U. prolifera CCMs in a low CO2 environment to explore the dynamic regulation of CCMs expression under inadequate inorganic carbon supply. The results showed that inorganic carbon limitation increased the inorganic carbon affinity of U. prolifera, upregulating CCMs. The first 24 h of inorganic carbon environmental changes were the most active period for U. prolifera's expression regulation. U. prolifera gradually achieved a new steady state by regulating metabolic processes such as nucleic acids, energy, and ethylene-activated signaling pathways. In the carbon fixation system of U. prolifera, there are characteristics of both biophysical and biochemical CCMs. After 24 h of inorganic carbon limitation, the biophysical CCMs becomes more effective under conditions of inorganic carbon depletion. This study aids in exploring the CCMs of U. prolifera and their evolution in response to environmental changes.

Scaling CO2 Electrolyzer Cell Area from Bench to Pilot.

To contribute meaningfully to carbon dioxide (CO2) emissions reduction, CO2 electrolyzer technology will need to scale immensely. Bench-scale electrolyzers are the norm, with active areas <5 cm2. However, cell areas on the order of 100s or 1000s of cm2 will be required for industrial deployment. Here, we study the effects of increasing cell area, scaling over 2 orders of magnitude from a 5 cm2 lab-scale cell to an 800 cm2 pilot plant-scale cell. A direct scaling of the bench-scale cell architecture to the larger area results in a ∼20% drop in ethylene (C2H4) selectivity and an increase in the parasitic hydrogen (H2) evolution reaction (HER). We instrument an 800 cm2 electrolyzer cell to serve as a diagnostic tool and determine that nonuniformities in electrode compression and flow-influenced local CO2 availability are the key drivers of performance loss upon scaling. Machining of an initial 800 cm2 cell results in a standard deviation in MEA compression that is 7-fold that of a similarly produced 5 cm2 cell (0.009 mm). Using these findings, we redesign an 800 cm2 cell for compression tolerance and increased CO2 transport and achieve an H2 FE in the revised 800 cm2 cell similar to that of the 5 cm2 case (16% at 200 mA cm-2). These results demonstrate that by ensuring uniform compression and fluid flow, the CO2 electrolyzer area can be scaled over 100-fold and retain C2H4 selectivity (within 10% of small-scale selectivity).

Rational Designing Microenvironment of Gas-Diffusion Electrodes via Microgel-Augmented CO2 Availability for High-Rate and Selective CO2 Electroreduction to Ethylene.

Efficient electrochemical CO2 reduction reaction (CO2RR) requires advanced gas-diffusion electrodes (GDEs) with tunned microenvironment to overcome low CO2 availability in the vicinity of catalyst layer. Herein, for the first time, pyridine-containing microgels-augmented CO2 availability is presented in Cu2O-based GDE for high-rate CO2 reduction to ethylene, owing to the presence of CO2-phil microgels with amine moieties. Microgels as three-dimensional polymer networks act as CO2 micro-reservoirs to engineer the GDE microenvironment and boost local CO2 availability. The superior ethylene production performance of the GDE modified by 4-vinyl pyridine microgels, as compared with the GDE with diethylaminoethyl methacrylate microgels, indicates the bifunctional effect of pyridine-based microgels to enhance CO2 availability, and electrocatalytic CO2 reduction. While the Faradaic efficiency (FE) of ethylene without microgels was capped at 43% at 300mAcm-2, GDE with the pyridine microgels showed 56% FE of ethylene at 700mAcm-2. A similar trend was observed in zero-gap design, and GDEs showed 58% FE of ethylene at -4.0 cell voltage (>350mAcm-2 current density), resulting in over 2-fold improvement in ethylene production. This study showcases the use of CO2-phil microgels for a higher rate of CO2RR-to-C2+, opening an avenue for several other microgels for more selective and efficient CO2 electrolysis.

Tailoring the interfacial microenvironment by electrolyte engineering boosts bicarbonate electrolysis

AbstractBicarbonate electrolysis, as a carbon utilization technology with high efficiency and potential for industrial applications, provides a promising pathway for CO2 emission reduction. However, how to inhibit serious hydrogen evolution reaction (HER) and increase the relatively low CO2 concentration at the electrode‐electrolyte interfacial is challenging. Here, we introduce three typical aminopolycarboxylic acids (APCAs) with different amounts of carboxylic acid roots into 3 M KHCO3 to enhance the Faradaic efficiency of CO (FECO) from 51.2% to 68.0% at 100 mA cm−2. Spectroscopic characterization confirms that the role of APCAs in confining the activity of water dissociation and improving the availability of CO2. The strategy adopted in this work that introducing APCAs into the electrolyte to balance the content of CO2 and H2O for improving the electrocatalytic performance, can serve as a reference for other electrocatalytic systems.

Coupling Microkinetics with Continuum Transport Models to Understand CO2R on Planar and Optimized Patterned Electrodes

Electrochemical CO2 reduction has emerged as an attractive technique to sustainably produce valuable fuels and chemicals, while reducing CO2 emissions. In addition to the specific electrode material, the microenvironment local to the electrode interface – e.g., the electrolyte pH, CO2 concentration, buffer concentration – plays a significant role in determining the selectivity and activity of the electrolyzer. In this work, we demonstrate a multi-scale approach, where microkinetic simulations of Au are coupled to a two-dimensional continuum transport model in a flow reactor configuration. Specifically, concentrations and potentials solved for in the continuum model are fed into microkinetic models along the planar electrode surface, which return concentration fluxes that are used to update the continuum model. We find that local quantities at the electrode interface, such as the CO2 concentration and pH, vary not only with the applied potential and flow rate, but also with position on the electrode. We investigate two ways to increase CO2 availability at the interface: (1) increasing the applied flow rate, thus reducing the boundary layer thickness, and (2) introducing an inert defect in the middle of the electrode, allowing CO2 to partially replenish within the depletion boundary layer. Inspired by the effect of a single inert defect, we explore electrodes patterned with inert defects and multiple catalyst materials, i.e. a generalized tandem system. We show how the specific pattern of the electrode can be optimized in order to target a specific desired product. The different parts of the electrode have different goals that work together: converting CO2 to CO, converting CO to C2+ products, and allowing concentrations to replenish through the boundary layer. Overall, our aim is to demonstrate the need for multi-dimensional, multi-scale approaches to simulating CO2 reduction to elucidate the reaction environment near the electrode.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-857537.

E-Methanol Production and Potential Export in the Northern Denmark Region for 2030 and 2045

Denmark has set a target of 4–6 GW electrolysis capacity by 2030, of which a part of the produced hydrogen is to be used for export, while the rest could be transformed further into electrofuels. The North Denmark Region has favourable conditions for the production of carbon-based fuels. The region has high availability of CO2 sources and a strategic position for establishing CO2 hubs in the local harbours that could support biogenic CO2 availability in the future. This paper investigates the potential of the region for exporting e-methanol through 22 energy system scenarios and the impacts on the energy system if this is to be realised by 2030 and 2045, when Denmark is expected to achieve its national climate goals. The analysis highlights the significant potential of this region to contribute to e-methanol production not only to meet the regional demand for methanol for marine transport and aviation but also for export to the rest of Denmark or beyond Danish borders.

Cation‐Infused Bilayer Ionomer Coating Enables High Partial Current Density Toward Multi Carbon Products in CO2 Electrolysis

AbstractElectrochemical CO2 reduction (eCO2R) stands as a pivotal technology for carbon recycling by converting CO2 into value‐added products. While significant strides have been made in generating multi‐carbon (C2+) products like ethylene (C2H4) and ethanol (C2H5OH) at industrial‐scale current densities with high Faradaic efficiency (FE), cathode flooding and (bi)carbonate salt accumulation remain a fundamental concern in an alkaline electrolyte. In this work, ion‐conducting polymers are used to tailor the micro‐environment mitigating cathode flooding and salt precipitation and thus, enhancing the local CO2 availability. The impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA‐9 are examined on overall eCO2R performance. The use of an ultra‐thin bilayer configuration significantly reduces cathode flooding and salt accumulation by ≈58% compared to commercial anion exchange membrane (AEM). Alongside, cation infusion improves the C─C bond formation inducing a favorable micro‐environment for selective C2+ formation. This cation‐infused bilayer ionomer (CIBLI) achieves a high partial current density of ≈284 mA cm−2 toward C2+ products maintaining a stable eCO2R performance for 24 hours (h). This scalable approach of directly deposited ultra‐thin CIBLI offers a minimal conversion energy of 117 GJ/ ton C2+ products with an energy efficiency (EE) of 29% at 350 mA cm−2 current density in one‐step CO2 conversion.

Effects of electrochemical active surface area of Cu on electrochemical CO2 reduction in acidic electrolyte using Cu nanoparticles on surfactant-treated carbon

Electrochemical carbon dioxide reduction reaction (CO2RR) presents a viable approach for transforming CO2 into valuable products. Traditional employment of neutral or alkaline electrolytes in CO2RR aims to avoid the hydrogen evolution reaction (HER). However, the usage of such electrolytes has intrinsic limitations on the availability of CO2 due to homogeneous equilibrium reactions, resulting in high energy costs for electrolyte regeneration. Lowering the pH of electrolytes can mitigate this concern and facilitate industrially relevant efficiencies. While recent studies show promising results for CO2RR in acidic environments using flow cells, the translation of conventional electrocatalysts from neutral or alkaline conditions to acidic conditions remains unclear. Hence, our investigation focuses on assessing the impact of surfactant-modified synthesis methods on CO2RR performance in acidic electrolytes.We first synthesized Cu nanoparticles on surfactant-treated carbon black by employing various surfactants: hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate, and Triton X-100, representing cationic, anionic, and nonionic surfactants, respectively. The objective of this synthesis was to investigate how surfactants influence the size and distribution of Cu nanoparticles (Cu NPs), the electrochemical active surface area (ECSA) of Cu, and, consequently, the performance of CO2RR in acidic electrolytes. The findings reveal that Cu NPs on carbon black show a different profile of size and distribution depending on the surfactant used for synthesis, resulting in varied ECSA. In addition, ECSA plays a crucial role in the production of C2H4 in an acidic medium, determining the onset potential and production rate of C2H4 while maintaining original Cu activity. In summary, surfactant treatment not only controls the size but also enables the uniform distribution of Cu NPs on carbon black. Consequently, Cu NPs exhibiting larger ECSA demonstrate enhanced efficiency in the production of C2H4 compared to counterparts with smaller ECSA under acidic environment.

Understanding the Temperature Effect on Carbon‐Carbon Coupling during CO2 and CO Electroreduction in Zero‐Gap Electrolyzers†

Comprehensive SummaryCu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) and CO reduction reaction (CORR) are of great interest due to their potential to produce carbon‐neutral and value‐added multicarbon (C2+) chemicals. In practice, CO2RR and CORR are typically operated at industrially relevant current densities, making the process exothermal. Although the increased operation temperature is known to affect the performance of CO2RR and CORR, the relationship between temperatures and kinetic parameters was not clearly elaborated, particularly in zero‐gap reactors. In this study, we detail the effect of the temperature on Cu‐catalyzed CO2RR and CORR. Our electrochemical and operando spectroscopic studies show that high temperatures increase the activity of CO2RR to CO and CORR to C2H4 by enhancing the mass transfer of CO2 and CO. As the rates of these two processes are highly influenced by reactant diffusion, elevating the operating temperature results in high local CO2 and CO availability to accelerate product formation. Consequently, the *CO coverage in both cases increases at higher temperatures. However, under CO2RR conditions, *CO desorption is more favorable than carbon‐carbon (C—C) coupling thermodynamically at high temperatures, causing the reduction in the Faradaic efficiency (FE) of C2H4. In CORR, the high‐temperature‐augmented CO diffusion overcomes the unfavorable adsorption thermodynamics, increasing the probability of C—C coupling.

Kinetics of In-Situ Calcium Magnesium Carbonate Precipitation and the Need for Desulfation in Seawater-Flooded Carbonate Reservoirs

Summary Mixing of incompatible injection and formation brines leads to the deposition of inorganic sulfate scales such as barite, celestite, and anhydrite in and around production wells. This process is well documented in seawater-flooded clastic reservoirs. One technique to avoid the resulting formation damage is to remove sulfate from seawater before injection using nanofiltration; however, this process is costly. We identify in this paper that it may not always be necessary in higher-temperature carbonate reservoirs. In this paper, we describe the use of reactive transport reservoir simulation to investigate the impact of carbon dioxide (CO2) partitioning and changes in pH, ionic concentrations, and temperature on carbonate reactivity and the sulfate scaling risk in waterflooded carbonate reservoirs. Dissolution and precipitation of calcite, dolomite, gypsum, anhydrite, barite, and celestite are all modeled and found to be coupled through (various) common ion effects. The produced brine compositions are used to calculate the saturation ratios (SRs) and mass of precipitate that may form in the production system. Sensitivity to mineral reaction kinetics, particularly for the dolomite reactions, is accounted for. Results identify that there is a strong relationship between calcite dissolution and dolomite (or other calcium/magnesium carbonate mineral) precipitation reactions, which drive each other and are affected by the availability of CO2 in the residual oil phase. This evolves over time, and as the thermal front propagates, impacts the concentration of calcium and magnesium in the brines traversing the reservoir. Temperature changes around the injection wellbore impact CO2 and mineral solubilities. The concentration of calcium in the displaced brine mix is thus determined more by contact with rock and temperature than by mixing between injection and formation brines. Depending on location relative to the thermal front, this may lead to gypsum or anhydrite precipitation, thereby stripping sulfate out of the injection brine. Thus, the sulfate scaling risk at the production wells is significantly reduced by this sulfate depletion process: The sulfate is stripped out of the seawater as it warms up in the reservoir before it mixes extensively with the formation water and significantly before any mixture of the two brines reaches the production zone. Thus, any loss of permeability is restricted to deep within the reservoir, where the pore volume (PV) that can accommodate mineral precipitation is very large. In this work, we identify that for carbonate reservoirs above 90–100°C, stripping of sulfate due to coupled mineral reactions may reduce or eliminate the need for use of a sulfate reduction plant (SRP). The process is modeled for the first time, accounting for the impact of CO2 partitioning and thermal front propagation. Knowledge of the kinetics of calcium/magnesium carbonate precipitation is shown to be critical in predicting the extent of sulfate depletion.

Effects of Zn loading on ZnxCo1−xCo2O4 spinel catalysts for low-temperature catalytic decomposition of N2O in the presence of inhibitors

The recent advancement of NH3-based fuel demands the development of catalysts that can decompose N2O at low temperatures and are stable against various inhibitors. Zn-doped cobalt spinel (ZnxCo1−xCo2O4) catalysts have demonstrated superior activity for N2O decomposition at low temperatures. However, their optimization and deactivation mechanisms with respect to Zn loading when inhibitors are present require further investigation. Herein, we reviewed the effects of Zn loading on catalysts at low temperatures without or with the presence of inhibitors (3 vol% O2, 6 vol% H2O, 200 ppm NO). The results showed that adding an appropriate amount of Zn into Co3O4 spinel catalysts improves their N2O decomposition activity. The Zn-induced enhancement of the catalysts’ redox properties, and reducibility was the underlying mechanism behind the activity promotion. The presence of structural defects created through the addition of Zn enhanced the catalyst’s resistance to O2. The deactivation by H2O and NO upon the addition of Zn could be correlated with the reduced availability of surface Co species and Co2+ as adsorption-active sites and the stronger bond of Co with –NO, respectively. This study underscores the importance of controlling the Zn loading as a bulk redox promoter in ZnxCo1−xCo2O4 spinel catalysts for practical applications.

Effect of internal moisture content (IMC) on the CO2 sequestration efficiency of hollow natural fiber (HNF)-reinforced reactive magnesia cement (RMC) composites

The incorporation of minor hollow natural fibers (HNF) can significantly accelerate the CO2 diffusion in reactive magnesia cement (RMC). The CO2 diffusivity in HNF is highly related to its internal moisture content (IMC), which subsequently affects the carbonation process of HNF-RMC, but this is outside the scope of the existing studies. Therefore, this work investigates the effect of IMC on carbonation, strength, and microstructure of HNF-RMC composites. HNF-RMC mortar specimens are dried to different levels of nominal IMC (0–100%), and cured under high CO2 concentration for carbonation. Following the curing, the matrix composition was characterized with varying techniques (QXRD, TGA, FTIR, and acid digestion) for quantifying the CO2 sequestration; the compressive strength at different depths was determined with uniaxial compressive test; the microstructure was examined with SEM/ESEM. The results show that the carbonation depth is increased by three to four times by reducing the IMC to 0%. The effects of varying IMC on local carbonation and strength are distinct in the shallow (0–20 mm) and middle/deep region (20–100 mm). In the shallow region, inadequate CO2 dissolution is the limiting factor, these performances decreased with the increasing desiccation. In the deeper regions, moisture absorption by HNF decreased the CO2 diffusivity, hence the CO2 availability is the limiting factor, and these performances increased with the desiccation. These observations suggest that the understanding that carbonation maximizes at a medium moisture level is not valid in HNF-RMC–controlling the moisture can be important for improving the CO2 sequestration and consequent mechanical strength.

Nutrient remobilization and C:N:P stoichiometry in response to elevated CO2 and low phosphorus availability in rice cultivars introgressed with and without Pup1

The continuously rising atmospheric CO2 concentration potentially increase plant growth through stimulating C metabolism; however, plant C:N:P stoichiometry in response to elevated CO2 (eCO2) under low P stress remains largely unknown. We investigated the combined effect of eCO2 and low phosphorus on growth, yield, C:N:P stoichiometry, and remobilization in rice cv. Kasalath (aus type), IR64 (a mega rice variety), and IR64-Pup1 (Pup1 QTL introgressed IR64). In response to eCO2 and low P, the C accumulation increased significantly (particularly at anthesis stage) while N and P concentration decreased leading to higher C:N and C:P ratios in all plant components (leaf, sheath, stem, and grain) than ambient CO2. The remobilization efficiencies of N and P were also reduced under low P with eCO2 as compared to control conditions. Among cultivars, the combined effect of eCO2 and low P was greater in IR64-Pup1 and produced higher biomass and grain yield as compared to IR64. However, IR64-Pup1 exhibited a lower N but higher P concentration than IR64, indicating that the Pup1 QTL improved P uptake but did not influence N uptake. Our study suggests that the P availability along with eCO2 would alter the C:N:P ratios due to their differential partitioning, thereby affecting growth and yield.

Limitations of Plant Stress Tolerance upon Heat and CO2 Exposure in Black Poplar: Assessment of Photosynthetic Traits and Stress Volatile Emissions.

Volatile organic compounds (VOCs) emitted by plants may help in understanding the status of a plant's physiology and its coping with mild to severe stress. Future climatic projections reveal that shifts in temperature and CO2 availability will occur, and plants may incur the uncoupling of carbon assimilation and synthesis of key molecules. This study explores the patterns of emissions of key VOCs (isoprene, methanol, acetaldehyde, and acetic acid) emitted by poplar leaves (more than 350) under a combined gradient of temperature (12-42 °C) and air CO2 concentration (400-1500 ppm), along with measurements of photosynthetic rates and stomatal conductance. Isoprene emission exhibited a rise with temperature and CO2 availability, peaking at 39 °C, the temperature at which methanol emission started to peak, illustrating the limit of stress tolerance to severe damage. Isoprene emission was uncoupled from the photosynthesis rate, indicating a shift from the carbon source for isoprene synthesis, while assimilation was decreased. Methanol and acetaldehyde emissions were correlated with stomatal conductance and peaked at 25 °C and 1200 ppm CO2. Acetic acid emissions lacked a clear correlation with stomatal conductance and the emission pattern of its precursor acetaldehyde. This study offers crucial insights into the limitations of photosynthetic carbon and stress tolerance.