CO2 Uptake Rate Research Articles

The impact of CO2 uptake rate on the environmental performance of cementitious composites: A new dynamic Global Warming Potential analysis

The sustainability of cementitious composites is currently analyzed by static methods, with little consideration of changes over time. In terms of Global Warming Potential (GWP), increasing the CO2 concentration in the atmosphere may negatively affect the planet. Therefore, estimating the imbalance between CO2 emitted and CO2 captured by these materials may be critical when assessing their environmental performance. This is the first study that proposes a new dynamic GWP method to analyze the sustainability of materials with the ability to uptake CO2 during their service life. For that, three main concrete mixtures are assessed: (i) a reference concrete with 100% Ordinary Portland cement (OPC); (ii) a concrete with 25% Fly Ash Class C (FA) + 75% OPC; and (iii) a concrete with 40% Ground Granulated Blast Furnace Slag (GGBFS) + 60% OPC. The investigation quantifies the GWP associated over a 100-year timeframe of a concrete mixture made at year 0 and based on four different CO2 uptake rates (reference, nano-modified A and B, and CO2 curing). Results demonstrate that while CO2-cured concretes exhibit the lowest GWP at year 0, nano-modified A concretes possess the lowest GWP associated at year 100 due to the acceleration of the CO2 uptake during their lifetime. Results also reveal that the GWP of nano-modified and CO2-cured concretes will be overestimated if the effects over time are not considered. Therefore, the dynamic methodology presented in this study should be employed when quantifying their GWP in cementitious composites. Moreover, this dynamic analysis could also be applied to other impact categories or even the complete holistic life cycle assessment.

Evaluation of carbon sink in the Taklimakan Desert based on correction of abnormal negative CO2 flux of IRGASON

Studies showing that deserts can sequester CO2 through non-photosynthetic processes have contributed to locating missing carbon sinks. However, the contradiction between the desert CO2 flux obtained by different observation methods leads to uncertainty in evaluating desert carbon sequestration. This has caused scepticism regarding desert carbon sequestration after years of research. Through a comparative experiment in the non-vegetated shifting sand of the Taklimakan Desert (TD), it was found that if the abnormal negative CO2 flux observed by IRGASON during the day was not corrected, the carbon sequestration of the TD would be overestimated. The CO2 flux observed by EC155 is highly consistent with that of LI-COR8100A and can reflect the real CO2 exchange in the desert. The CO2 flux observed by EC155 was used to correct the results of IRGASON. Results show that the expansion/contraction of soil air containing CO2 caused by the change in the daily average soil temperature difference (T0-10cm) drives CO2 exchange in shifting sand. This results in diurnal variation of CO2 release caused by shifting sand during the day and CO2 absorption at night, and a unimodal distribution of CO2 exchange caused by shifting sand throughout the year. From April to September (T0-10cm > 2 °C), the shifting sand releases CO2 as a carbon source. In the other months (T0-10cm < 2 °C), the shifting sand absorbs CO2 as a carbon sink. The stronger absorption shows that the shifting sand in the TD provides carbon sequestration, with a CO2 uptake rate of ~148.85 × 104 tons a-1. This suggests that deserts play an active role in locating the missing carbon sinks and mitigating climate change, and that the status of deserts in the global carbon cycle cannot be ignored.

LIGHT INTENSITY AND ACTIVITY OF TRYPSIN INHIBITORS IN AMARANTH LEAVES AND SEEDS

The effect of exposing Amaranthus hypochondriacus plants to different levels of photosynthetic photon flux densities (PPFD) duringdevelopment was analyzed in this work. Mature plants exposed to full sunlight (38.8 mol m-2 d-1) had higher instantaneous rates of net CO2 uptake (An), reducing sugars content and thicker leaves, but lower chlorophyll content and leaf number per plant than those developed under reduced levels of PPFD (19.4 and 12.8 mol m-2 d-1). A physiological response to varying levels of PPFD was the differential accumulation of trypsin inhibitors in leaves and seeds. Leaves from plants grown under full sunlight conditions, showed a significantly higher trypsin inhibitor activity than leaves from plants partially shaded with plastic nets. In contrast, seeds collected from plants fully exposed to sunlight, showed the lowest level of trypsin inhibitors and higher rates of germination than seeds produced by plants exposed to the lowest level of sunlight. The capacity of A. hypochondriacus to adjust its morphology and physiology in response to light indicates ecological plasticity that might be helpful to face both biotic and abiotic stresses during their development.

Early Wintertime CO2 Uptake in the Western Arctic Ocean

AbstractTo investigate CO2 uptake in the western Arctic Ocean (north of 65°N), we conducted underway, ship‐based observations of the partial pressures of CO2 (pCO2) and total dissolved inorganic carbon (TCO2) in surface seawater in early winter (November 2018). From these two properties of the seawater inorganic carbon system, we calculated total alkalinity (TA). In the early winter, surface seawater pCO2 in most places was lower than atmospheric pCO2. The weighted mean of the air‐sea influxes of CO2 were calculated to be 7.5 ± 1.6 mmol m−2 d−1. The calculated influxes imply that the area acted as a moderate sink for atmospheric CO2 in early winter, and its rate of CO2 uptake was comparable to that (8.0 ± 1.7 mmol m−2 d−1) in summer (late August−September 2017). Spatial variations of surface seawater pCO2 in the early winter could be attributed mostly to conservative mixing changes of TCO2 and TA, which together accounted for more than 70% of the pCO2 variations. In the marginal ice zone, however, there was a decrease of surface seawater pCO2 by 70–90 μatm because of horizontal advection of water with an anomalously high temperature from the Pacific Ocean and its subsequent cooling. We concluded that mixing of water masses was as important as biological processes in causing spatial variations of pCO2 and CO2 uptake in the western Arctic Ocean, especially during seasons and in areas associated with little biological activity.

Enhanced weathering potentials—the role of in situ CO2 and grain size distribution

The application of rock powder on agricultural land to ameliorate soils and remove carbon dioxide (CO2) from the air by chemical weathering is still subject to many uncertainties. To elucidate the effects of grain size distribution and soil partial pressure of carbon dioxide (pCO2) levels on CO2 uptake rates, two simple column experiments were designed and filled nearly daily with an amount of water that simulates humid tropical conditions, which prevail in areas known for being hotspots of weathering. Multiple materials (dunite, basanite, agricultural oxisol, a combination of the latter two, and loess) were compared under ambient and 100% CO2 atmosphere. In a second series, single material columns (dunite) were filled with three different grain size distributions. Total alkalinity, pH, major ions, and dissolved silica were determined in the outflow water of the columns for about 300 days. Under ambient atmospheric conditions, the CO2 consumption was the lowest in the oxisol column, with 100 t CO2 km−2 year−1, while dunite and basanite showed similar consumption rates (around 220 t CO2 km−2 year−1). The values are comparable to high literature values for ultramafic lithologies. Interestingly, the mixture of basanite and oxisol has a much higher consumption rate (around 430 t CO2 km−2 year−1) than the basanite alone. The weathering fluxes under saturated CO2 conditions are about four times higher in all columns, except the dunite column, where fluxes are increased by a factor of more than eleven. Grain size distribution differences also play a role, with the highest grain surface area normalized weathering rates observed in the columns with coarser grains, which at first seems counterintuitive. Our findings point to some important issues to be considered in future experiments and a potential rollout of EW as a carbon dioxide removal method. Only in theory do small grain sizes of the spread-material yield higher CO2 drawdown potentials than coarser material. The hydrologic conditions, which determine the residence times in the pore space, i.e., the time available for weathering reactions, can be more important than small grain size. Saturated-CO2 column results provide an upper limit for weathering rates under elevated CO2.

Cellulose acetate based sustainable nanostructured membranes for environmental remediation

Membrane-based gas separation has a great potential for reducing environmentally hazardous carbon dioxide (CO2) gas. The polymeric membranes developed for CO2 capturing have some limitations in their selectivity and permeability. There is a need to overcome these issues and developed such membranes having high-performance CO2 capture with cost-effectiveness. The present study aimed to synthesize mixed matrix membranes (MMMs) having improved properties CO2 adsorption performance and stability than that of pure polymer. Further, the effect on CO2 adsorption by increasing the filler concentration in MMMs was investigated. The MMMs were synthesized by incorporating (1–5 wt%) Cu-MOF-GO composites as filler into cellulose-acetate (CA) polymer matrix by adopting the solution casting method. The performance of MMMs was studied by changing the Cu-MOF-GO composite concentration (1–5 wt%) in the polymer matrix at 45 °C up to 15 bar. Morphological analysis by using SEM confirms that by increasing the concentration of Cu-MOF-GO more than 3% will result in their agglomeration in MMM. The successful incorporation of MOF within the polymer matrix of MMMs was confirmed through the presence of functional groups using FTIR and Raman spectroscopy. XRD analysis revealed that pure CA changes its semi-crystalline behaviour into crystalline by the addition of Cu-MOF-GO. The maximum tensile stress and strain rate of MMMs was 45.1 N/mm2 and 12.8%. In addition, with an increase in (4–5 wt%) Cu-MOF-GO concentration the hydrophilicity of MMMs decreases. The maximum uptake rate of CO2 was 1.79 mmol/g and 7.98 wt% at 15 bar. The adsorption results conclude that Cu-MOF-GO composite and CA-based MMM can be effective for CO2 capture.

The evolution of diffusive and biochemical capacities for photosynthesis was predominantly shaped by [CO2] with a smaller contribution from [O2

The atmospheric concentration of carbon dioxide ([CO2]) and oxygen ([O2]) directly influence rates of photosynthesis (PN) and photorespiration (RPR) through the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO). Levels of [CO2] and [O2] have varied over Earth history affecting rates of both CO2 uptake and loss, alongside associated transpirative water-loss. The availability of CO2 has likely acted as a stronger selective pressure than [O2] due to the greater specificity of RubisCO for CO2. The role of [O2], and the interaction of [O2] and [CO2], in plant evolutionary history is less understood. We exposed twelve phylogenetically diverse species to combinations of sub-ambient, ambient and super-ambient [O2] and [CO2] to examine the biochemical and diffusive components of PN and the possible role of [O2] as a selective pressure. Photosynthesis, photosynthetic capacity and stomatal, mesophyll and total conductance to CO2 were higher in the derived eudicot and monocot angiosperms than the more basal ferns, gymnosperms and basal angiosperms which originated in atmospheres characterised by higher CO2:O2 ratios. The ratio of RPR:PN was lower in the monocots, consistent with greater carboxylation capacity and higher stomatal and mesophyll conductance making easier CO2 delivery to chloroplasts. The effect of [O2] and [CO2] on PN/RPR was less evident in more derived species with a higher conductance to CO2. The effect of [O2] was less apparent at high [CO2], suggesting that atmospheric [O2] may only have exerted a strong selective pressure on plant photosynthetic processes during periods characterised by low atmospheric CO2:O2 ratios. Current rising [CO2] will predominantly enhance PN rates in species with low diffusive conductance to CO2.

CO2 capture and water use efficiency in Opuntia stricta (Haw.) at different seasons and evaluation times

The forage cactus Mexican Elephant Ear is widely incorporated into the animal productive chain of the northeast region of Brazil. However, there is a lack of studies on the physiological dynamics of this cactus. Therefore, this study was conducted at the Estação Experimental Prof. Ignácio Salcedo of the Instituto Nacional do Semiárido (INSA), in Campina Grande, State of Paraíba, Brazil. The aim of this study was to evaluate CO2 uptake and water-use efficiency levels in Opuntia stricta (Haw.) during different seasons and evaluation times. The treatments were distributed using a 24×2 factorial arrangement, which corresponded to the evaluation of gas exchange processes for 24 hours in the rainy (June) and dry (December) seasons. The evaluated parameters were stomatal conductance, transpiration and CO2 uptake rate, internal CO2 concentration, instantaneous water-use efficiency and intrinsic water-use efficiency. The results revealed that gas exchange in the forage cactus was more intense during the rainy season, with good stability, than the low exchange levels during the dry season. Regardless of the season, the CO2 uptake peaked between 24:00 and 02:00. In addition, this range of time is the most suitable to conduct analyses under field conditions.

Short-Term Exposure to Thermophilic Temperatures Facilitates CO Uptake by Thermophiles Maintained under Predominantly Mesophilic Conditions.

Three phylogenetically and phenotypically distinct CO-oxidizing thermophiles (Alicyclobacillus macrosporangiidus CPP55 (Firmicutes), Meiothermus ruber PS4 (Deinococcus-Thermus) and Thermogemmatispora carboxidovorans PM5T (Chloroflexi)) and one CO-oxidizing mesophile (Paraburkholderia paradisi WAT (Betaproteobacteria)) isolated from volcanic soils were used to assess growth responses and CO uptake rates during incubations with constant temperatures (25 °C and 55 °C) and during multi-day incubations with a temperature regime that cycled between 20 °C and 55 °C on a diurnal basis (alternating mesophilic and thermophilic temperatures, AMTT). The results were used to test a conjecture that some thermophiles can survive in mesothermal habitats that experience occasional thermophilic temperatures. Meiothermus ruber PS4, which does not form spores, was able to grow and oxidize CO under all conditions, while the spore-forming Alicyclobacillus macrosporangiidus CPP55 grew and oxidized CO during the AMTT regime and at 55 °C, but was not active at 25 °C. Thermogemmatispora carboxidovorans PM5T, also a spore former, only grew at 55 °C but oxidized CO during AMTT and 55 °C incubations. In contrast, the non-sporing mesophile, Paraburkholderia paradisi WAT, was only able to grow and oxidize CO at 25 °C; growth and CO uptake ceased during the AMTT incubations after exposure to the initial round of thermophilic temperatures. Collectively, these results suggest that temporary, periodic exposure to permissive growth temperatures could help maintain populations of thermophiles in mesothermal habitats after deposition from the atmosphere or other sources.

Ca2CuO3: A high temperature CO2 sorbent with rapid regeneration kinetics

Three different calcium-based ternary oxide sorbents, Ca2CuO3, Ca3Co4O9, and Ca2Fe2O5, were characterized as potential sorbents for CO2 capture. The behaviors of these sorbents were compared to CaO under various CO2 concentrations via temperature programmed carbonation/decarbonation. Ca2CuO3 and Ca3Co4O9 showed lower inversion temperatures, while Ca2Fe2O5 had a higher inversion temperature than CaO. In addition, the copper and cobalt containing sorbents showed relatively narrower temperature windows going from the highest carbonation rate to the highest decarbonation rate. This narrow temperature window can be advantageous in operating a temperature swing process. Ca3Co4O9 and Ca2Fe2O5 showed low conversion. Under the best-case scenario, the conversion of these sorbents was less than 25%. Ca2CuO3 showed faster regeneration compared to CaO when the sorbent temperature was cycled between 700 and 800 °C. In addition, we found 740–850 °C for Ca2CuO3 and 640–900 °C for CaO as the temperature swing windows of the best reaction rates. The narrower range of operational temperature (110 °C for Ca2CuO3 compared to 260 °C for CaO) can lead to higher overall rate of CO2 uptake and release. Ca2CuO3 showed 60% higher cycle-averaged decarbonation rate compared to CaO when cycled between the temperatures of maximum carbonation and decarbonation rates

Photosynthetic and Morphological Responses of Sacha Inchi (Plukenetia volubilis L.) to Waterlogging Stress.

Sacha inchi (Plukenetia volubilis L.) is an important oilseed crop that is rich in fatty acids and protein. Climate-change-related stresses, such as chilling, high temperature, and waterlogging can cause severe production loss in this crop. In this study, we investigated the photosynthetic responses of sacha inchi seedlings to short-term waterlogging and their morphological changes after long-term waterlogging stress. Sacha inchi CO2 uptake, stomatal conductance, and transpiration rate are affected by temperature and light intensity. The seedlings had a high CO2 uptake (>10 μmol m−2s−1) during the daytime (08:00 to 15:00), and at 32 and 36 °C. At 32 °C, CO2 uptake peaked at irradiations of 1000 and 1500 µmol m−2s−1, and plants could still perform photosynthesis at high-intensity radiation of 2000–3000 µmol m−2s−1. However, after 5 days of waterlogging (5 DAF) sacha inchi seedlings significantly reduced their photosynthetic ability. The CO2 uptake, stomatal conductance, Fv/Fm, ETR, and qP, etc., of the susceptible genotypes, were significantly decreased and their wilting percentage was higher than 50% at 5 DAF. This led to a higher wilting percentage at 7 days post-recovery. Among the four lines assessed, Line 27 had a high photosynthetic capability and showed the best waterlogging tolerance. We screened many seedlings for long-term waterlogging tolerance and discovered that some seedlings can produce adventitious roots (AR) and survive after two weeks of waterlogging. Hence, AR could be a critical morphological adaptation to waterlogging in this crop. In summary, these results suggest that improvement in waterlogging tolerance has considerable potential for increasing the sustainable production of sacha inchi.

Gulf ribbed mussels increase plant growth, primary production, and soil nitrogen cycling potential in salt marshes

Smooth cordgrass Spartina alterniflora and Atlantic ribbed mussels Geukensia demissa have a mutualism whereby S. alterniflora provides substrate and shade for G. demissa while G. demissa enhances S. alterniflora growth and drought tolerance. Together, these species improve salt marsh stability and function. To better understand if a similar relationship exists between S. alterniflora and Gulf ribbed mussels G. granosissima in salt marshes of the Gulf of Mexico, we conducted a manipulative experiment with identical starting plant density and varying densities of G. granosissima and monitored plant and soil responses over a growing season. We found that S. alterniflora stem and leaf density was 1.5 and 1.9 times greater for the highest mussel biomass compared to the lowest mussel biomass treatments. Similarly, above- and below-ground biomass were 2.6 and 3.2 times greater for the highest mussel biomass compared to the lowest mussel biomass treatments. More and larger S. alterniflora at higher G. granosissima densities resulted in 2 and 4 times the S. alterniflora gross CO2 uptake and respiration rate, respectively. Methane fluxes were highest when G. granosissima were present, likely driven by the positive relationship between methane flux and belowground biomass. Net potential nitrification was 5 times higher for the highest mussel biomass compared to the lowest mussel biomass treatments, and denitrification rates were 1.8 times higher. Ultimately, our results suggest that G. granosissima increases S. alterniflora growth and productivity, much like the positive relationship between G. demissa and S. alterniflora, which in turn influences salt marsh stability and function.

A strong mitigation scenario maintains climate neutrality of northern peatlands

A strong mitigation scenario maintains climate neutrality of northern peatlands

Carbon Accumulation, Flux, and Fate in Stordalen Mire, a Permafrost Peatland in Transition

AbstractStordalen Mire is a peatland in the discontinuous permafrost zone in arctic Sweden that exhibits a habitat gradient from permafrost palsa, to Sphagnum bog underlain by permafrost, to Eriophorum‐dominated fully thawed fen. We used three independent approaches to evaluate the annual, multi‐decadal, and millennial apparent carbon accumulation rates (aCAR) across this gradient: seven years of direct semi‐continuous measurement of CO2 and CH4 exchange, and 21 core profiles for 210Pb and 14C peat dating. Year‐round chamber measurements indicated net carbon balance of −13 ± 8, −49 ± 15, and −91 ± 43 g C m−2 y−1 for the years 2012–2018 in palsa, bog, and fen, respectively. Methane emission offset 2%, 7%, and 17% of the CO2 uptake rate across this gradient. Recent aCAR indicates higher C accumulation rates in surface peats in the palsa and bog compared to current CO2 fluxes, but these assessments are more similar in the fen. aCAR increased from low millennial‐scale levels (17–29 g C m−2 y−1) to moderate aCAR of the past century (72–81 g C m−2 y−1) to higher recent aCAR of 90–147 g C m−2 y−1. Recent permafrost collapse, greater inundation and vegetation response has made the landscape a stronger CO2 sink, but this CO2 sink is increasingly offset by rising CH4 emissions, dominated by modern carbon as determined by 14C. The higher CH4 emissions result in higher net CO2‐equivalent emissions, indicating that radiative forcing of this mire and similar permafrost ecosystems will exert a warming influence on future climate.

Comparison of kinetics and thermochemical energy storage capacities of strontium oxide, calcium oxide, and magnesium oxide during carbonation reaction

In this work kinetics of carbonation reaction of strontium oxide was investigated using the well-known random pore model. This non-catalytic gas-solid reaction can be utilized both for carbon capture and storage (CCS) and thermochemical energy storage (TCES) applications. In order to obtain kinetic parameters and reaction rate equation, a set of experiments ranging from 800 °C to 950 °C in temperature and 5 to 40 vol% in concentration of CO2 were conducted. It was concluded that fractional function describes the concentration dependency of reaction rate very well. The activation energy of this reaction was calculated to be about 64 kJ/mol and the best exponential function indicating temperature dependency of CO2 diffusivity through the product layer was also estimated. Furthermore, it was attempted to depict the importance of this reaction for CCS and TCES purposes. This goal was achieved by comparing our results with those of around 50 similar researches carried on MgO, CaO, and SrO-based sorbents. Comparison was done using six screening criteria; i.e. CO2 uptake, CO2 uptake rate, conversion, conversion rate, thermal energy, and thermal power.

Cutover Peat Limits Methane Production Causing Low Emission at a Restored Peatland

AbstractPeatland degradation due to human activities is contributing to rising atmospheric CO2 levels. Restoring the carbon (C) sink function in degraded peatlands and preventing further stored C losses is a key climate mitigation strategy, given the global scale of peatland disturbance. Active restoration involving a combination of rewetting and vegetation reestablishment at a post‐extraction peatland in Canada has been shown to successfully re‐establish net CO2 uptake rates similar to undisturbed peatlands within a decade or two. However, lower than expected CH4 emissions suggest recovery of belowground C cycling processes may lag behind the recovery of the surface net flux. Using closed chamber measurements over a warm season, we determined that restored Sphagnum, which covers two thirds of the site, was a null source of CH4. Emissions from the restored site were primarily attributed to vascular plant substrate inputs, measured as acetate, and plant‐mediated transport. The C isotopic fractionation factor for CH4 and CO2 in the pore water from the restored former peat field suggested reduced hydrogenotrophic CH4 production deeper in the cutover peat profile (0.8 m depth). In contrast, isotopic fractionation in the former drainage ditches showed a balance of acetoclastic and hydrogenotrophic methanogenesis deeper in the profile, indicative of some bulk peat C turnover. This study suggests that the legacy of substrate quality in the cutover peat can reduce the climate warming impact of newly restored peatlands through a reduction in CH4 production and thus emission.

Hurricane Michael Altered the Structure and Function of Longleaf Pine Woodlands

AbstractTropical cyclones can physically alter ecosystems, causing immediate and potentially long‐lasting effects on carbon dynamics. In 2018, Hurricane Michael hit the southeastern United States with category 5 winds at landfall and category 2 winds reaching over 100 miles inland, resulting in extensive damage. Longleaf pine woodlands in the path of the hurricane were damaged, but severity varied based on the storm track. We used a combination of eddy covariance measurements, airborne LiDAR, and forest inventory data to determine whether hurricane affects structure, function, and recovery of two longleaf pine woodlands at the ends of an edaphic gradient. We found that the carbon sink potentials in both sites were diminished following the storm, with reductions in net ecosystem exchange (NEE) primarily due to lower rates of photosynthesis, as respiration only increased marginally. The xeric site carbon losses and physiological reductions were smaller following the disturbance, which led to the recovery of ecosystem physiological activity to prestorm rates before that of the mesic site, as indicated by maximum ecosystem CO2 uptake rates. Two years following the hurricane both stands continued to have reduced NEE, which signaled altered function. We expect both locations to recover their lost carbon stocks in ∼10–35 years; however, long‐term studies are needed to examine how longleaf woodlands respond to compounding disturbances, such as drought, fire, or other wind storms, which vary significantly across the ecosystem's range. Additionally, hurricanes are intensifying due to climate change, potentially amplifying the degree to which they will alter this ecosystem in the future.

Hydrate‐Based CO2 Capture through Nano Dry Gels + Tetrahydrofuran – A Kinetic and Thermodynamic Study

AbstractThe synergic effects of four combinations of nano dry gels plus tetrahydrofuran (THF) on the CO2 capture and hydrate phase equilibrium were investigated. It was found that the hydrate phase equilibrium condition was almost identical with the mixture of nano dry gel + THF and THF solution. The gas storage capacity and CO2 uptake rate increased significantly by THF concentration increment up to 19.06 wt % in the dry gel structure compared to a similar THF solution. The hydrate induction time decreased at higher ratios of THF. The mixture of dry gel + THF acted as a stabilizer during the hydrate dissociation process. Considering the gas storage capacity, kinetics, and thermodynamic promoting effect, a mixture including 19.06 wt % THF was favorable for hydrate‐based CO2 capture compared to the other combinations investigated in this study.

Prolonged impacts of extreme precipitation events weakened annual ecosystem CO2 sink strength in a coastal wetland

It remains unclear whether coastal wetlands could maintain the expected carbon sink role since extreme climate events are predicted to occur more frequently under future climate change. Among these extreme events, extreme precipitation may cause significant changes in ecosystem carbon stocks in coastal wetlands. However, the impacts of extreme precipitation events on carbon cycle processes and the mechanisms responsible for associated changes in the ecosystem carbon balance remain uncertain. To address this issue, we investigated the effects of extreme precipitation events on the ecosystem carbon dioxide (CO2) budget based on a 10-year eddy covariance dataset (2010-2019) at a coastal wetland in the Yellow River Delta. Results showed that this coastal wetland was a stable sink for CO2, with the annual net ecosystem CO2 exchange (NEE) ranged between -94.49 and -240.70 g C m−2 yr−1. Meanwhile, the interannual variability of the ecosystem CO2 sink strength in the dry stage was linked to the vegetation condition, and it was strongly affected by extreme precipitation events in the wet stage. During the wet stage, there was a clear trend of less negative daily NEE (i.e., lower CO2 uptake rate) in the years with extreme precipitation events occurring (extreme years) than in normal years, leading to the wet stage cumulative CO2 uptake being 56% lower in extreme years. Eventually, the coastal wetland became a weaker annual CO2 sink due to the prolonged impact of the extreme precipitation event. This research provides a timely study of the effect of extreme precipitation on ecosystem CO2 budget in coastal wetlands and should be of value to researchers attempting to assess the future impact of climate change on coastal ecosystems.

Potential metabolic mechanisms for inhibited chloroplast nitrogen assimilation under high CO2.

Improving photosynthesis is considered a major and feasible option to dramatically increase crop yield potential. Increased atmospheric CO2 concentration often stimulates both photosynthesis and crop yield, but decreases protein content in the main C3 cereal crops. This decreased protein content in crops constrains the benefits of elevated CO2 on crop yield and affects their nutritional value for humans. To support studies of photosynthetic nitrogen assimilation and its complex interaction with photosynthetic carbon metabolism for crop improvement, we developed a dynamic systems model of plant primary metabolism, which includes the Calvin–Benson cycle, the photorespiration pathway, starch synthesis, glycolysis–gluconeogenesis, the tricarboxylic acid cycle, and chloroplastic nitrogen assimilation. This model successfully captures responses of net photosynthetic CO2 uptake rate (A), respiration rate, and nitrogen assimilation rate to different irradiance and CO2 levels. We then used this model to predict inhibition of nitrogen assimilation under elevated CO2. The potential mechanisms underlying inhibited nitrogen assimilation under elevated CO2 were further explored with this model. Simulations suggest that enhancing the supply of α-ketoglutarate is a potential strategy to maintain high rates of nitrogen assimilation under elevated CO2. This model can be used as a heuristic tool to support research on interactions between photosynthesis, respiration, and nitrogen assimilation. It also provides a basic framework to support the design and engineering of C3 plant primary metabolism for enhanced photosynthetic efficiency and nitrogen assimilation in the coming high-CO2 world.