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The components of the mediator kinase module are highly conserved across all eukaryotic lineages, and cyclin‐dependent kinase 8 (CDK8) is essential for correct cell proliferation and differentiation in diverse eukaryotic systems. We show that CDK8 couples leaf development with the establishment of correct stomata patterning for prevailing CO2 conditions. In Arabidopsis, the basic helix‐loop‐helix (bHLH) transcription factor SPEECHLESS (SPCH) controls cellular entry into the stomatal cell lineage, and CDK8 interacts with and phosphorylates SPCH, controlling SPCH protein levels and thereby also expression of the SPCH target genes encoding key regulators of cell fate and asymmetric cell divisions. The lack of the CDK8‐mediated control of SPCH results in an increased number of meristemoid and guard mother cells, and increased stomata index in the cdk8 mutants. Increasing atmospheric CO2 concentrations trigger a developmental programme controlling cell entry into stomatal lineage by limiting the asymmetric divisions. In cdk8, the number of meristemoids and guard mother cells remains the same under ambient and high CO2 concentrations, as the accumulated levels of SPCH caused by the lack of CDK8 appear to override the negative regulation of increased CO2. Thus, our work provides novel mechanistic understanding of how plants alter critical leaf properties in response to increasing atmospheric CO2. Summary Statement: The components of the mediator kinase module are highly conserved across eukaryotic lines and cyclin‐dependent kinase 8 (CDK8) is essential for correct cell proliferation and development. We show here that control of leaf development is closely linked to the establishment of correct stomata patterning through the impact of CDK8. Comprehending the plasticity of plant morphology and the mechanisms behind it is essential for our understanding of plant environmental responses and the consequences of climate change. [ABSTRACT FROM AUTHOR]

Abstract Background Estimating the CO2 response of forest trees is of great significance in plant photosynthesis research. CO2 response measurement is traditionally employed under steady state conditions. With the development of open-path gas exchange systems, the Dynamic Assimilation Technique (DAT), allows measurement under non-steady state conditions. This greatly improves the efficiency and data density of CO2 response measurement. This study aims to assess the accuracy and effectiveness of different models in fitting DAT data, addressing the current gap in verification of model performance. Results This research was conducted for three common broadleaf tree species (Ulmus macrocarpa, Fraxinus mandshurica, and Tilia amurensis) in North Eastern China. Among the three species, Fraxinus mandshurica is the most adapted to high CO2 concentration conditions. Four models were compared, the rectangular hyperbola (RH) model, the Michaelis-Menten (MM) model, the modified rectangular hyperbola (MRH) model and a non-rectangular hyperbola (NRH) model. Conclusions Considering the model parsimony and parameter accuracy, the NRH model emerged as the best choice (R2 = 0.9966, RMSE = 0.1862, AIC=-199.86). This study provides a reference for the further application of DAT in the field of photosynthesis.

To investigate the dynamics of stomata, transpiration, and photosynthesis under varying light intensities and CO2 conditions during leaf development, the light response and CO2 response of stomatal conductance (gsw), transpiration rate (Tr), and net photosynthetic rate (Pn) were observed for rice leaves at different days after leaf emergence (DAE). The results showed that (1) as photosynthetically active radiation (PAR) increased, leaf gsw, Tr, and Pn initially increased rapidly and linearly, followed by a more gradual rise to maximum values, and then either stabilized or showed a declining trend. The maximum gsw, Tr, and Pn were smaller and occurred earlier for old leaves than for young leaves. The gsw, Tr, and Pn all exhibited a linear decreasing trend with increasing DAE, and the rate of decrease slowed down with the reduction in PAR; (2) as the CO2 concentration (Ca) increased, gsw and Tr decreased gradually to a stable minimum value, while Pn increased linearly and slowly up to the maximum and then kept stable or decreased. The gsw, Tr, and Pn values initially kept high and then decreased with the increase of DAE. These results contribute to understanding the dynamics in gsw, Tr, and Pn during rice leaf growth and their response to varied light and CO2 concentration conditions and provide mechanistic support to estimate dynamic evapotranspiration and net ecosystem productivity at field-scale and a larger scale in paddy field ecosystems through the upscaling of leaf-level stomatal conductance, transpiration, and photosynthesis. [ABSTRACT FROM AUTHOR]

Addressing the issue of inadequate temperature tolerance in traditional polymers, in this study, we successfully executed a one-step synthesis of intelligent–responsive polymers which have excellent adaptability in water–gas alternating displacement scenarios. Utilizing the fatty acid method, we produced OANND from oleic acid (OA) and N,N-dimethyl-1,3-propanediamine (NND). Upon testing the average particle size in the aqueous solution both prior and subsequent to CO2 passage, it became evident that OANND assumes the form of a small-molecule particle in the aqueous phase, minimizing damage during formation. Notably, upon CO2 exposure, it promptly organizes into stable micelles with an average size of 88 nm and a relatively uniform particle distribution. This unique characteristic endows it with a rapid CO2 response mechanism and the ability to form a highly resilient gel. In the exploration of viscoelastic fluids, we observed the remarkable behavior of the AONND aqueous solution when CO2/N2 was introduced. This system displayed repeatable transitions between aqueous and gel states, with the highest viscosity peaking at approximately 3895 mPa·s, highlighting its viscosity reversibility and reusability properties. The rheological property results that we obtained indicate that an elongated micellar structure is present in the solution system, with the optimal concentration ratio for its formation determined as 0.8, which is the molar ratio of the OANND-NaOA system. In the sealing performance tests, a 1.0 wt% concentration of the gel system exhibited excellent injectability properties. At 80 °C, this gel effectively reduced the permeability of a sand-filled model to 94.5% of its initial value, effectively sealing potential leakage paths or gas fluxes. This remarkable ability to block leakage paths and reduce seepage capacity highlights the material's superior blocking effect and erosion resistance properties. Furthermore, even at a temperature of 90 °C and an injection pore volume (PV) of 3, this plugging system could reduce the permeability of a high-permeability sand-filled model to over 90% of its initial value. [ABSTRACT FROM AUTHOR]

Summary: Radiation use efficiency (RUE) is a key crop adaptation trait that quantifies the potential amount of aboveground biomass produced by the crop per unit of solar energy intercepted. But it is unclear why elite maize and grain sorghum hybrids differ in their RUE at the crop level. Here, we used a non‐traditional top‐down approach via canopy photosynthesis modelling to identify leaf‐level photosynthetic traits that are key to differences in crop‐level RUE.A novel photosynthetic response measurement was developed and coupled with use of a Bayesian model fitting procedure, incorporating a C4 leaf photosynthesis model, to infer cohesive sets of photosynthetic parameters by simultaneously fitting responses to CO2, light, and temperature.Statistically significant differences between leaf photosynthetic parameters of elite maize and grain sorghum hybrids were found across a range of leaf temperatures, in particular for effects on the quantum yield of photosynthesis, but also for the maximum enzymatic activity of Rubisco and PEPc.Simulation of diurnal canopy photosynthesis predicted that the leaf‐level photosynthetic low‐light response and its temperature dependency are key drivers of the performance of crop‐level RUE, generating testable hypotheses for further physiological analysis and bioengineering applications. [ABSTRACT FROM AUTHOR]

To investigate the dynamics of stomata, transpiration, and photosynthesis under varying light intensities and CO2 conditions during leaf development, the light response and CO2 response of stomatal conductance (gsw), transpiration rate (Tr), and net photosynthetic rate (Pn) were observed for rice leaves at different days after leaf emergence (DAE). The results showed that (1) as photosynthetically active radiation (PAR) increased, leaf gsw, Tr, and Pn initially increased rapidly and linearly, followed by a more gradual rise to maximum values, and then either stabilized or showed a declining trend. The maximum gsw, Tr, and Pn were smaller and occurred earlier for old leaves than for young leaves. The gsw, Tr, and Pn all exhibited a linear decreasing trend with increasing DAE, and the rate of decrease slowed down with the reduction in PAR; (2) as the CO2 concentration (Ca) increased, gsw and Tr decreased gradually to a stable minimum value, while Pn increased linearly and slowly up to the maximum and then kept stable or decreased. The gsw, Tr, and Pn values initially kept high and then decreased with the increase of DAE. These results contribute to understanding the dynamics in gsw, Tr, and Pn during rice leaf growth and their response to varied light and CO2 concentration conditions and provide mechanistic support to estimate dynamic evapotranspiration and net ecosystem productivity at field-scale and a larger scale in paddy field ecosystems through the upscaling of leaf-level stomatal conductance, transpiration, and photosynthesis.

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Phase-transfer processes between immiscible liquids play a prominent part in various applications, particularly for separation and recovery of catalysts. Zeolitic-imidazolate frameworks (ZIFs), as a specific subset of metal–organic frameworks, have been proven to be encouraging candidates for catalysts or cocatalysts because of their appealing characteristics, whereas recovery and reusability of ZIFs still remain a challenge because of their submicrometer-to-micrometer size. In this work, a kind of amino-modified ZIF-90 was designed and prepared, and by adjusting the hydrophobicity and hydrophilicity of surface species, these ZIFs could reversibly transfer between organic solvents and water by alternate bubbling of CO2 and N2. It was found that the mechanism of the phase transfer was aroused from the reversible formation of hydrophilic salts upon CO2 addition. By employing this novel property of the functionalized ZIF-90, an efficient and regulable CuI-catalyzed cycloaddition was fulfilled wherein the amino-modified ZIF-90 was applied to encapsulate, activate and reuse the catalyst, and regulate the reaction. [ABSTRACT FROM AUTHOR]

Using steady-state photosynthesis–intercellular CO2 concentration (A–Ci) response curves to obtain the maximum rates of ribulose-1,5-bisphosphate carboxylase oxygenase carboxylation (Vcmax) and electron transport (Jmax) is time-consuming and labour-intensive. Instead, the rapid A–Ci response (RACiR) technique provides a potential, high-efficiency method. However, efficient parameter settings of RACiR technique for evergreen broadleaved species remain unclear. Here, we used Li-COR LI-6800 to obtain the optimum parameter settings of RACiR curves for evergreen broadleaved trees and shrubs. We set 11 groups of CO2 gradients ([CO2]), i.e. R1 (400–1500 ppm), R2 (400–200–800 ppm), R3 (420–20–620 ppm), R4 (420–20–820 ppm), R5 (420–20–1020 ppm), R6 (420–20–1220 ppm), R7 (420–20–1520 ppm), R8 (420–20–1820 ppm), R9 (450–50–650 ppm), R10 (650–50 ppm) and R11 (650–50–650 ppm), and then compared the differences between steady-state A–Ci and RACiR curves. We found that Vcmax and Jmax calculated by steady-state A–Ci and RACiR curves overall showed no significant differences across 11 [CO2] gradients (P > 0.05). For the studied evergreens, the efficiency and accuracy of R2, R3, R4, R9 and R10 were higher than the others. Hence, we recommend that the [CO2] gradients of R2, R3, R4, R9 and R10 could be applied preferentially for measurements when using the RACiR technique to obtain Vcmax and Jmax of evergreen broadleaved species. [ABSTRACT FROM AUTHOR]

Degradable magnetic and CO2 dual-responsive microgels were prepared by inverse suspension polymerization and in-situ synthesis of nanoparticles. The structure and morphology of microgels were characterized by Fourier-transformed infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The microgels exhibited magnetic and CO2 responsiveness, and could be degraded upon the treatment of D, L-dithiothreitol (DTT). After treating with the stimulus of CO2, the microgels exhibited a selective adsorption for anionic dyes. The maximum adsorption capacity was up to 1413 mg/g for Alizarin red (AR). The microgels with adsorbates could be separated from solutions under the help of an external magnetic field. Besides, the adsorbates could be described by treating with solution of pH 12. Microgels regenerated with CO2 trigger exhibited high adsorption ability (>90%) after three consecutive recycling trials. [ABSTRACT FROM AUTHOR]

Photosynthetic responses to CO2 were followed on leaves of Malus domestica cv. Cox's Orange trees growing in orchard conditions, before and after harvest. Rates of photosynthesis, at ambient and CO2 saturated concentrations, were stable across the growing season, except for minor decreases at harvest although rates recovered and remained high thereafter. Stomatal conductance increased over the growing season but declined transiently just before harvest and recovered for most of the season. Rates of ribulose-1,5-bisphosphate (RuBP) carboxylation declined before harvest, however, rates of RuBP regeneration mirrored assimilation. After harvest, rates of RuBP regeneration increased whereas rates of carboxylation increased but remained low, limiting photosynthesis. Lack of change in photosynthesis after harvest was at odds with the literature where photosynthesis of high crop load trees declined soon after, suggesting crop load was not as demanding on the Cox's Orange trees as in other studies.

CO2‐responsive CCT protein (CRCT) is a positive regulator of starch synthesis–related genes such as ADP‐glucose pyrophosphorylase large subunit 1 and starch branching enzyme I particularly in the leaf sheath of rice (Oryza sativa L.). The promoter GUS analysis revealed that CRCT expressed exclusively in the vascular bundle, whereas starch synthesis–related genes were expressed in different sites such as mesophyll cell and starch storage parenchyma cell. However, the chromatin immunoprecipitation (ChIP) using a FLAG‐CRCT overexpression line and subsequent qPCR analyses showed that the 5′‐flanking regions of these starch synthesis–related genes tended to be enriched by ChIP, suggesting that CRCT can bind to the promoter regions of these genes. The monomer of CRCT is 34.2 kDa; however, CRCT was detected at 270 kDa via gel filtration chromatography, suggesting that CRCT forms a complex in vivo. Immunoprecipitation and subsequent MS analysis pulled down several 14‐3‐3‐like proteins. A yeast two‐hybrid analysis and bimolecular fluorescence complementation assays confirmed the interaction between CRCT and 14‐3‐3‐like proteins. Although there is an inconsistency in the place of expression, this study provides important findings regarding the molecular function of CRCT to control the expression of key starch synthesis–related genes. CO2‐responsive CCT protein (CRCT) is a positive regulator of starch synthesis in vegetative organs of rice. Here we show that CRCT can interact with 14‐3‐3 proteins and controls the transcription of key starch synthesis–related genes such as ADP‐glucose pyrophosphorylase large subunit 1. [ABSTRACT FROM AUTHOR]

A novel hemoglobin (Hb) imprinted polymers with CO2 response (CHIPs) were prepared on the surface of Au electrode modified by zinc oxide (CHIPs/ZnO/Au) via electrochemically mediated atom transfer radical polymerization (eATRP). The imprinted polymers were synthesized with Hb both as catalyst and template, and N,N-diethylaminoethyl methacrylate (DEAEMA) as CO2-responsive functional monomer. The obtained CHIPs/ZnO/Au electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The results showed that CHIPs/ZnO/Au electrode could give higher affinity for the target protein inside a CO2-treated aqueous medium compared to that under N2-treated conditions, which make it a good electrochemical biosensor in the presence of CO2. The biosensor could be successfully applied for the determination of Hb by differential pulse voltammetry (DPV) measurement. The linear response range of CHIPs/ZnO/Au for detecting Hb was 1.0×10−12~1.0×10−1 mg L−1 and the detection limit was 2.1×10−13 mg L−1 (S/N=3). Briefly, the work in this study introduced an easy and non-toxic method for Hb determination under specific conditions and also provided a progressive approach for designing protein imprinted polymers. [ABSTRACT FROM AUTHOR]

Interventions to increase crop radiation use efficiency rely on understanding of how biochemical and stomatal limitations affect photosynthesis. When leaves transition from shade to high light, slow increases in maximum Rubisco carboxylation rate and stomatal conductance limit net CO2 assimilation for several minutes. However, as stomata open intercellular [CO2] increases, so electron transport rate could also become limiting. Photosynthetic limitations were evaluated in three important Brassica crops: Brassica rapa, Brassica oleracea and Brassica napus. Measurements of induction after a period of shade showed that net CO2 assimilation by B. rapa and B. napus saturated by 10 min. A new method of analyzing limitations to induction by varying intercellular [CO2] showed this was due to co‐limitation by Rubisco and electron transport. By contrast, in B. oleracea persistent Rubisco limitation meant that CO2 assimilation was still recovering 15 min after induction. Correspondingly, B. oleracea had the lowest Rubisco total activity. The methodology developed, and its application here, shows a means to identify the basis of variation in photosynthetic efficiency in fluctuating light, which could be exploited in breeding and bioengineering to improve crop productivity. Slow, Rubisco‐ and stomata‐limited post‐shade induction was evaluated in three Brassica species. Net CO2 uptake in Brassica oleracea was persistently Rubisco‐limited and took >15 min to recover after shade; in Brassica napus and Brassica rapa, recovery was faster, <10 min, due to co‐limitation by electron transport. [ABSTRACT FROM AUTHOR]

The rising concentration of atmospheric carbon dioxide (CO2) is known to increase the total aboveground biomass of several C3 crops, whereas C4 crops are reported to be hardly affected when water supply is sufficient. However, a free‐air carbon enrichment (FACE) experiment in Braunschweig, Germany, in 2007 and 2008 resulted in a 25% increased biomass of the C4 crop maize under restricted water conditions and elevated CO2 (550 ppm). To project future yields of maize under climate change, an accurate representation of the effects of eCO2 and drought on biomass and soil water conditions is essential. Current crop growth models reveal limitations in simulations of maize biomass under eCO2 and limited water supply. We use the coupled process‐based hydrological‐plant growth model Catchment Modeling Framework‐Plant growth Modeling Framework to overcome this limitation. We apply the coupled model to the maize‐based FACE experiment in Braunschweig that provides robust data for the investigation of combined CO2 and drought effects. We approve hypothesis I that CO2 enrichment has a small direct‐fertilizing effect with regard to the total aboveground biomass of maize and hypothesis II that CO2 enrichment decreases water stress and leads to higher yields of maize under restricted water conditions. Hypothesis III could partly be approved showing that CO2 enrichment decreases the transpiration of maize, but does not raise soil moisture, while increasing evaporation. We emphasize the importance of plant‐specific CO2 response factors derived by use of comprehensive FACE data. By now, only one FACE experiment on maize is accomplished applying different water levels. For the rigorous testing of plant growth models and their applicability in climate change studies, we call for datasets that go beyond single criteria (only yield response) and single effects (only elevated CO2). [ABSTRACT FROM AUTHOR]

Summary: Steady‐state photosynthetic CO2 responses (A/Ci curves) are used to assess environmental responses of photosynthetic traits and to predict future vegetative carbon uptake through modeling. The recent development of rapid A/Ci curves (RACiRs) permits faster assessment of these traits by continuously changing [CO2] around the leaf, and may reveal additional photosynthetic properties beyond what is practical or possible with steady‐state methods.Gas exchange necessarily incorporates photosynthesis and (photo)respiration. Each process was expected to respond on different timescales due to differences in metabolite compartmentation, biochemistry and diffusive pathways. We hypothesized that metabolic lags in photorespiration relative to photosynthesis/respiration and CO2 diffusional limitations can be detected by varying the rate of change in [CO2] during RACiR assays. We tested these hypotheses through modeling and experiments at ambient and 2% oxygen.Our data show that photorespiratory delays cause offsets in predicted CO2 compensation points that are dependent on the rate of change in [CO2]. Diffusional limitations may reduce the rate of change in chloroplastic [CO2], causing a reduction in apparent RACiR slopes under high CO2 ramp rates.Multirate RACiRs may prove useful in assessing diffusional limitations to gas exchange and photorespiratory rates. [ABSTRACT FROM AUTHOR]

Photosynthetic responses to CO2 were followed on leaves of Malus domestica cv. Cox's Orange trees growing in orchard conditions, before and after harvest. Rates of photosynthesis, at ambient and CO2 saturated concentrations, were stable across the growing season, except for minor decreases at harvest although rates recovered and remained high thereafter. Stomatal conductance increased over the growing season but declined transiently just before harvest and recovered for most of the season. Rates of ribulose-1,5-bisphosphate (RuBP) carboxylation declined before harvest, however, rates of RuBP regeneration mirrored assimilation. After harvest, rates of RuBP regeneration increased whereas rates of carboxylation increased but remained low, limiting photosynthesis. Lack of change in photosynthesis after harvest was at odds with the literature where photosynthesis of high crop load trees declined soon after, suggesting crop load was not as demanding on the Cox's Orange trees as in other studies. [ABSTRACT FROM AUTHOR]

Summary: Mesophyll conductance (gm) describes the movement of CO2 from the intercellular air spaces below the stomata to the site of initial carboxylation in the mesophyll. In contrast with C3‐gm, little is currently known about the intraspecific variation in C4‐gm or its responsiveness to environmental stimuli. To address these questions, gm was measured on five maize (Zea mays) lines in response to CO2, employing three different estimates of gm. Each of the methods indicated a significant response of gm to CO2. Estimates of gm were similar between methods at ambient and higher CO2, but diverged significantly at low partial pressures of CO2. These differences are probably driven by incomplete chemical and isotopic equilibrium between CO2 and bicarbonate under these conditions. Carbonic anhydrase and phosphoenolpyruvate carboxylase in vitro activity varied significantly despite similar values of gm and leaf anatomical traits. These results provide strong support for a CO2 response of gm in Z. mays, and indicate that gm in maize is probably driven by anatomical constraints rather than by biochemical limitations. The CO2 response of gm indicates a potential role for facilitated diffusion in C4‐gm. These results also suggest that water‐use efficiency could be enhanced in C4 species by targeting gm. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southern Agriculture is the property of Journal of Southern Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plants always adjust the opening of stomatal pores to adapt to the environment, for example CO2 concentration ([CO2]), humidity and temperature. Low [CO2] will trigger the opening of stomatal pores to absorb extra CO2. However, little is known about how CO2 supply affects the carbon fixation and opening of stomatal pores in rice. Here, a chloroplast-located gene coding for β-carbonic anhydrase (βCA) was found to be involved in carbon assimilation and the CO2-mediated stomatal pore response in rice. Osβ CA1 was constitutively expressed in all tissues and its transcripts were induced by high [CO2] in leaves. Both T-DNA mutant and RNA interference lines showed phenotypes of lower biomass and CA activities. Knockout of Osβ CA1 obviously decreased photosynthetic capacity, as demonstrated by the increased CO2 compensation point and decreased light saturation point in the mutant, while knockout increased the opening ratio of stomatal pores and the rate of water loss. Moreover, the mutant showed a delayed response to low [CO2], and stomatal pores could not be closed to the same degree as those of wild type even though the stomatal pores could rapidly respond to high [CO2]. Genome-wide gene expression analysis via RNA sequencing demonstrated that the transcript abundance of genes related to Rubisco, photosystem compounds and the opening of stomatal pores was globally upregulated in the mutant. Taken together, the inadequate CO2 supply caused by the absence of Osβ CA1 reduces photosynthetic efficiency, triggers the opening of stomatal pores and finally decreases their sensitivity to CO2 fluctuation. [ABSTRACT FROM AUTHOR]

With the increasing demand for oil and gas resources, deep tight oil and gas reservoirs have gradually become the focus of global oil and gas exploration and development. Hydraulic fracturing technology based on water-base fracturing fluid plays a more and more important role in improving the recovery of tight oil reservoirs. Under the background of global CO 2 emission reduction, a CO 2 -responsive clean fracturing fluid with controllable gelling/gel breaking at high temperatures was constructed in this paper. The system was not only friendly to the reservoir and environment, but also overcame the shortcomings of the traditional clean fracturing fluid with undesirable temperature resistance. The viscosity characteristics and viscoelastic behavior of temperature-resistant clean fracturing fluid were investigated through high-temperature rheology experiments. The interaction between fluid and rock was investigated through the core flow experiment. The results showed that the clean fracturing fluid had the characteristics of good CO 2 responsiveness, excellent shear resistance at high temperatures, high drag reduction, satisfactory gel breaking performance, low filtration and low core damage. The complex three-dimensional network structure formed by the intertwined micelles and vesicles improves the temperature resistance of the clean fracturing fluid. It is expected that the fluid can not only be used to improve oil recovery in tight oil reservoirs, but also be used to solve the leakage problem in CO 2 storage underground. [Display omitted] • CO 2 -responsive clean fracturing fluid with excellent temperature resistance. • Fluid characteristics of high drag reduction, low filtration and low core damage. • Complex three-dimensional network structure improves the temperature resistance. • Application potential of tight oil reservoirs and CO 2 sequestration reservoirs. [ABSTRACT FROM AUTHOR]

HT1 (HIGH LEAF TEMPERATURE 1) is the first component associated with changes in stomatal aperture in response to CO2 to be isolated by forward genetic screening. The HT1 gene encodes a protein kinase expressed mainly in guard cells. The loss-of-function ht1-1 and ht1-2 mutants in Arabidopsis thaliana have CO2-hypersensitive stomatal closure with concomitant reductions in their kinase activities in vitro. In addition to these mutants, in this study we isolate or obtaine five new ht1 alleles (ht1-3, ht1-4, ht1-5, ht1-6, and ht1-7). Among the mutants, only ht1-3 has a dominant mutant phenotype and has widely opened stomata due to CO2 insensitivity. The ht1-3 mutant has a missense mutation affecting a non-conserved residue (R102K), whereas the other six recessive mutants have mutations in highly conserved residues in the catalytic domains required for kinase activity. We found that the dominant mutation does not affect the expression of HT1 or the ability to phosphorylate casein, a universal kinase substrate, but it does affect autophosphorylation activity in vitro. A 3D structural model of HT1 also shows that the R102 residue protrudes from the surface of the kinase, implying a role for the formation of oligomers and/or interaction with its targets. We demonstrate that both the loss-of-function and gain-of-function ht1 mutants have completely disrupted CO2 responses, although they have normal responses to ABA. Furthermore, light-induced stomatal opening is smaller in ht1-3 and much smaller in ht1-2. Taken together, these results indicate that HT1 is a critical regulator for CO2 signaling and is partially involved in the light-induced stomatal opening pathway. [ABSTRACT FROM AUTHOR]

Photosynthesis determines the growth and dry matter accumulation of rice, and drought and waterlogging stress can inhibit the photosynthesis of rice. Study on the light response curve would help to understand the photosynthetic characteristics of rice in a more detailed way. Pot experiments were performed to research the effects of alternative stress of drought and waterlogging (ASDW) at tillering and jointing stage on rice leaf photosynthesis, light response and CO2 response, including net photosynthetic rate, stomatal conductance, potential water use efficiency and intercellular carbon dioxide concentration. Four treatments were set up in 2013 at tillering stage of rice (the water depth of waterlogging was 10 cm) including light drought (T-LD) and severe drought (T-HD), at jointing stage (the water depth of waterlogging was 15 cm) including light drought (S-LD) and severe drought (S-HD). Irrigation with water depth at 0-5 cm except for drying yellow ripening stage (CK) was the control. The experiments were conducted in the greenhouse of Key Laboratory of Efficient Irrigation-Drainage and Agricultural Soil-Water Environment in Southern China (Hohai University), Ministry of Education. The results indicated that rice leaf photosynthesis was inhibited by ASDW at the both tillering and jointing stage, and photosynthetic capacity recovered as the stress changing from drought to waterlogging; At the end of water stress, the net photosynthetic rate of T-HD treatment was lower than that of T-LD and CK (P＜0.01); The stomatal conductance of T-LD and T-HD treatment was reduced by 72.93% and 85.01% and the intercellular carbon dioxide concentration was also significantly lower than CK, but the potential water use efficiency was more than two times of CK; The net photosynthetic rate of S-HD treatment was significantly lower than that of CK (P＜0.01), while S-LD was lower than CK by 18.66%; The stomatal conductance of S-LD was close to CK, and that of S-HD was 62.73% lower than that of CK (P＜0.01); and The intercellular carbon dioxide concentration of S-LD and S-HD treatments showed an increasing trend, and S-LD was 21.57% higher than CK (P＜0.05), S-HD reached 1.50 times of CK, but potential water use efficiency of S-HD and S-LD treatments were lower than that of CK, and S-HD was 29.58% lower than CK (P＜0.01). After stress, water stress treatments showed obvious compensation effect; On October 10th, the net photosynthetic rate, stomatal conductance, and intercellular carbon dioxide concentration of water stress treatments were significantly higher than those of CK (P＜0.05); The potential water use efficiency of S-LD treatment was higher than that of other water stress treatments, but was still lower than CK by 21.35%. The net photosynthetic rate of water stress treatments was lower than CK under the same light intensity, but the light compensation point (LCP), light saturation point (LSP) and dark respiration rate were higher than that of CK, and net photosynthetic rate of rice CO2 response curve was increased. In the tillering stage, the photosynthetic capacity of the light drought treatment was strong, which was weak of the light drought treatment at jointing stage. But in the ripening period, photosynthetic rate of the two severe drought stress treatments were higher than that of light drought treatments. Alternative stress of drought and waterlogging decreased the maximal rate of photosynthesis, but improve the carboxylation efficiency, change the photosynthetic rate turning point of CO2 response curve. After the stress, increasing the light intensity appropriately and prolong the illumination time would be conducive to the rapid growth of rice. But the final yield of each treatment was significantly lower than that of CK (P＜0.05). The results can provide valuable information for analyzing the accumulation of dry matter and irrigation water use efficiency of rice, and further proved that drought stress in the early did not reduce the ability of waterlogging tolerance of rice in the late, and slight drought-waterlogging stress in the early stage would be helpful for enhancing rice drought ability from the perspective of photosynthesis. [ABSTRACT FROM AUTHOR]

[Objective] This study aimed to investigate the photosynthetic characteristics of different Prunus domestica × armeniaca cultivars, thereby providing some theoretical basis for high-yield and high-quality cultivation of P. domestica × armeniaca. [Method] Total three cultivars (Konglongdan, Fengwei Huanghou and Weiwang) of P. domestica × armeniaca were selected as the test materials, and their leafphotosynthetic parameters were measured with Li-6400 portable photosynthesis system. The light response curve and CO2 response curve were drawn. [Result] There were significant differences in photosynthetic rate among the three cultivars of P. domestica × armeniaca (P<0.01). The photosynthetic rate of Konglongdan [14.76 μmol/(m2·s)] was highest. When the light intensity reached 1 800 μmol/(m2·s), the maximum net photosynthetic rate of Konglongdan was up to 27.27 μmol/(m2·s), and its apparent quantum yield reached the peak. Konglongdan showed lower light compensation point [43.069 μmol/(m2·s)] and higher light saturation point [697.684 μmol/(m2·s)]. Weiwang showed the lowest CO2 compensation point (68.264 μmol/mol) and the highest carboxylic efficiency [0.072 μmol/(m2·s)]. [Conclusion] Konglongdan showed the highest light utilization efficiency and photosynthetic potential, and it had the strongest utilization ability for weak light. The utilization ability of Weiwang for low-concentration CO2 was strongest, fol owed by those of Fengwei Huanghou and Konglongdan. [ABSTRACT FROM AUTHOR]

The intelligent responsive membranes have aroused much attention due to their distinctive capability to reversibly change separation performances under the stimulation of ambient environment. Especially, the responsive membranes derived from block copolymers, which have regular nanoporous structures, display great potential in high-precision controllable separation. Herein, we use CO 2 gas as the non-toxic, mild stimulus, and develop the responsive membranes from a block copolymer of poly(2-diethylaminoethyl methacrylate)-block-polystyrene (PDEAEMA- b -PS) by the selective swelling method. The membranes exhibit a bi-continuous nanoporous structure and the surfaces and pore walls are rich with CO 2 -responsive PDEAEMA chains. Based on the reversible conformation transition of PDEAEMA chains between the collapsed state and extended state upon CO 2 /N 2 stimulation, the membranes achieve the controllable regulation on the water permeances from ∼100 to ∼2100 L⋅h−1⋅m−2⋅bar−1, also realize the blocking/passing switch for varied proteins. More importantly, the extended PDEAEMA chains shrink the effective pore size down to less than 5 nm, moving the separation scope from ultrafiltration to tight-ultrafiltration. Thus, the membranes are capable to separate macromolecular proteins with small molecule polypeptide and vitamin with high separation efficiencies, demonstrating their application prospect in precise separation and fractionation of biomolecules. [Display omitted] • CO2-responsive membranes were prepared via selective swelling of block copolymer. • The membranes achieve the regulation on blocking/passing switch for proteins. • The water permeance can be regulated from ∼100 to ∼2100 L⋅h−1⋅m−2⋅bar−1. • The membranes are capable to separate biomolecules with high efficiencies. [ABSTRACT FROM AUTHOR]

Isoprene emission is typically modelled using independent controls of light, temperature, and ambient [CO2], assuming these are unaffected by growth [CO2]. We demonstrated strong interactive environmental controls on emissions, calling for profound revision of emission algorithms.Plant isoprene emissions have been modelled assuming independent controls by light, temperature and atmospheric [CO2]. However, the isoprene emission rate is ultimately controlled by the pool size of its immediate substrate, dimethylallyl diphosphate (DMADP), and isoprene synthase activity, implying that the environmental controls might interact. In addition, acclimation to growth [CO2] can shift the share of the control by DMADP pool size and isoprene synthase activity, and thereby alter the environmental sensitivity. Environmental controls of isoprene emission were studied in hybrid aspen (Populus tremula × Populus tremuloides) saplings acclimated either to ambient [CO2] of 380 μmol mol–1 or elevated [CO2] of 780 μmol mol–1. The data demonstrated strong interactive effects of environmental drivers and growth [CO2] on isoprene emissions. Light enhancement of isoprene emission was the greatest at intermediate temperatures and was greater in elevated-[CO2]-grown plants, indicating greater enhancement of the DMADP supply. The optimum temperature for isoprene emission was higher at lower light, suggesting activation of alternative DMADP sinks at higher light. In addition, [CO2] inhibition of isoprene emission was lost at a higher temperature with particularly strong effects in elevated-[CO2]-grown plants. Nevertheless, DMADP pool size was still predicted to more strongly control isoprene emission at higher temperatures in elevated-[CO2]-grown plants. We argue that interactive environmental controls and acclimation to growth [CO2] should be incorporated in future isoprene emission models at the level of DMADP pool size. [ABSTRACT FROM AUTHOR]

Plant growth and metabolism are regulated in response to various environmental factors. To investigate modulations in plant metabolism by the combined action of elevated atmospheric CO2 concentration and other nutritional factors, we performed targeted metabolomic analysis using Arabidopsis thaliana plants grown under 24 different conditions where the CO2 concentration, amounts and species of nitrogen source, and light intensity were modified. Our results indicate that both the biosynthesis of diverse metabolites and growth are promoted in proportion to the CO2 concentration at a wide range of CO2 levels, from ambient concentrations to an extremely high concentration (3,600 p.p.m.) of CO2. This suggests that A. thaliana has the potential to utilize effectively very high concentrations of CO2. On the other hand, ammonium (but not nitrate) supplied as an additional nitrogen source induced drastic alterations in metabolite composition, including increases in the contents of glucose, starch and several amino acids, and reductions in the tricarboxylic acid (TCA) cycle-related organic acid content under any CO2 conditions. Hierarchical clustering analysis using the metabolite profiles revealed that ammonium is a prominent factor determining metabolic status, while the CO2 concentration is not. However, ammonium-induced metabolic alterations were differently modified by high concentrations of CO2. Hence, our results imply that increases in CO2 concentration may differently influence plant metabolism depending on the nitrogen nutrient conditions. [ABSTRACT FROM AUTHOR]

Previous studies have suggested that the mesophyll contributes to stomatal CO2 responses., The effects of changes in CO2 concentration (100 or 700 ppm) on stomatal responses in red or white light were examined microscopically in a leaf segment, an epidermal strip and an epidermal strip placed on a mesophyll segment of Commelina communis, all mounted on a buffer-containing gel., In both red and white light, stomata of the leaf segment opened/closed rapidly at low/high CO2. In red light, epidermal strip stomata barely responded to CO2. In white light, they opened at low CO2, but hardly closed at high CO2. Stomata of the epidermal strip placed on the mesophyll responded in the same manner as those on the leaf segment. Insertion of a doughnut-shaped cellophane spacer (but not polyethylene spacer) between the epidermal strip and the mesophyll hardly altered these responses. Stomata in leaf segments treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea ( DCMU), a photosynthesis inhibitor, did not open in red light, but opened/closed at low/high CO2 in white light., These results indicate that the apoplast transfer of 'mesophyll signals' and the stomatal opening at low CO2 are dependent on photosynthesis, whereas the stomatal closure at high CO2 is independent of photosynthesis. [ABSTRACT FROM AUTHOR]

Taking the two-year old potted Prunus sibirica seedlings as test materials, and using CIRAS-2 photosynthetic system, this paper studied the CO2 response process of P. sibirica photosynthesis in semi-arid loess hilly region under eight soil moisture conditions. The CO2 response data of P. sibirica were fitted and analyzed by rectangular hyperbola model, exponential equation, and modified rectangular hyperbola model. Meanwhile, the quantitative relationships between the photosynthesis and the soil moisture were discussed. The results showed that the CO2 response process of P. sibirica photosynthesis had obvious response characteristics to the soil moisture threshold. The relative soil water content (RWC) required to maintain the higher photosynthetic rate (Pn) and carboxylation efficiency (CE) of P. sibirica was in the range of 46. 3% -81. 9%. In this RWC range, the photosynthesis did not appear obvious CO2 saturated inhibition phenomenon. When the RWC exceeded this range, the photosynthetic capacity (Pn max ), CE, and CO2 saturation point (CSP) decreased evidently. Under different soil moisture conditions, there existed obvious differences among the three models in simulating the CO2 response data of P. sibirica. When the RWC was in the range of 46. 3% -81. 9%, the CO2 response process and the characteristic parameters such as CE, CO2 compensation point (Γ), and photorespiration rate (Rp) could be well fitted by the three models, and the accuracy was in the order of modified rectangular hyperbola model > exponential equation > rectangular hyperbola model. When the RWC was too high or too low, namely, the RWC was >81. 9% or <46. 3%, only the modified rectangular hyperbola model could well fit the CO2 response process and the characteristic parameters. It was suggested that when the RWC was from 46.3% to 81. 9%, the photosynthetic efficiency of P. sibirica was higher, and, as compared with rectangular hyperbola model and exponential equation, modified rectangular hyperbola model had more applicability to fit the CO2 response data of P. sibirica photosynthesis under different soil moisture conditions. [ABSTRACT FROM AUTHOR]

Approximately 1-2% of net primary production by land plants is re-emitted to the atmosphere as isoprene and monoterpenes. These emissions play major roles in atmospheric chemistry and air pollution-climate interactions. Phenomenological models have been developed to predict their emission rates, but limited understanding of the function and regulation of these emissions has led to large uncertainties in model projections of air quality and greenhouse gas concentrations. We synthesize recent advances in diverse fields, from cell physiology to atmospheric remote sensing, and use this information to propose a simple conceptual model of volatile isoprenoid emission based on regulation of metabolism in the chloroplast. This may provide a robust foundation for scaling up emissions from the cellular to the global scale. [ABSTRACT FROM AUTHOR]

Carbon dioxide served as a proxy for biodegradation in the biofiltration of multiple organic solvents in a batch biofilter. The solvents were injected into the batch biofilter system and were biodegraded with the biomass immobilized on a column of fibrous media; the immobilized biomass was acclimated to ethanol in a continuous biofilter. Time profiles of CO2 concentration were obtained for substrate utilization and for biomass endogenous respiration. The CO2 and substrate concentration profiles provided insight for the biodegradation of multiple substrates in a biofilter. Experimental results indicate that the biomass utilized the solvents simultaneously but at different rates. The utilization rates were in the order: acetaldehyde > ethanol > propanol > isopropanol, acetone > methanol > butanol. Isopropanol was transformed to acetone, which was then utilized and converted to CO2, and propanol was also utilized through the formation of an intermediate. The biodegradation of ethanol was inhibited by acetaldehyde. Total CO2 production was contributed by the endogenous respiration of the biomass as well as by the biodegradation of all the substrates present to the biomass, and the total CO2 rate might not reach its maximum potential. [ABSTRACT FROM AUTHOR]

Increased atmospheric CO2 concentration (Ca) produces a short-term stimulation of photosynthesis and plant growth across terrestrial ecosystems. However, the long-term response remains uncertain and is thought to depend on environmental constraints. In the longest experiment on natural ecosystem response to elevatedCa, we measured the shoot-density, biomass and net CO2 exchange (NEE) responses to elevatedCafrom 1987 to 2003 in aScirpus olneyiwetland sedge community of the Chesapeake Bay, MD, USA. Measurements were conducted in five replicated open-top chambers per CO2 treatment (ambient and elevated). In addition, unchambered control plots were monitored for shoot density. Responses of daytime NEE,Scirpusplant biomass and shoot density to elevatedCawere positive for any single year of the 17-year period of study. Daytime NEE stimulation by elevatedCarapidly dropped from 80% at the onset of the experiment to a long-term stimulation average of about 35%. Shoot-density stimulation by elevatedCaincreased linearly with duration of exposure (r2=0.89), exceeding 120% after 17 years. Although of lesser magnitude, the shoot biomass response to elevatedCawas similar to that of the shoot density. Daytime NEE response to elevatedCawas not explained by the duration of exposure, but negatively correlated with salinity of the marsh, indicating that this elevated-Caresponse was decreased by water-related stress. By contrast, circumstantial evidence suggested that salinity stress increased the stimulation of shoot density by elevatedCa, which highlights the complexity of the interaction between water-related stresses and plant community responses to elevatedCa. Notwithstanding the effects of salinity stress, we believe that the most important finding of the present research is that a species response to elevatedCacan continually increase when this species is under stress and declining in its natural environment. This is particularly important because climate changes associated with elevatedCaare likely to increase environmental stresses on numerous species and modify their present distribution. Our results point to an increased resilience to change under elevatedCawhen plants are exposed to adverse environmental conditions. [ABSTRACT FROM AUTHOR]

The aim of the study was to evaluate the microsphere technique for the quantitative assessment of regional cerebral blood flow (rCBF) at different time points in the same animal. Yellow–green and red fluorescent microspheres with a diameter of 15 μm were injected into the rat at two different time points via a cannula inserted into the left ventricle of the heart. The reproducibility of the rCBF measurements in normocapnic conditions (n=7) and the responsiveness of the flow to hypercapnia induced by 7% CO2 (n=7) was examined. The fluorescent spheres were counted on 100 μm vibratome sections of perfusion-fixed brains and rCBF was calculated. The median total CBF in normocapnic rats was 224 ml/min/100 g for the first microsphere injection and 216 ml/min/100 g for the second one. In the hypercapnic group CBF amounted to 400 ml/min/100 g and after 30 min of normocapnia decreased to 178 ml/min/100 g. No differences between the left and right hemisphere were found and there was no indication that the first injection might have influenced the second one. The described approach allows combining the assessment of rCBF at different time points in physiological or pathological conditions with histological evaluation of related morphological alterations in the same brain region of the same animal. [Copyright &y& Elsevier]

In this study we evaluated the feasibility of measuring cerebral blood flow in rats by monitoring the transit of an indocyanine green bolus through the brain with multiwavelength near-infrared spectroscopy. Different volumes of a 1 mg/ml indocyanine green solution (5, 15, 25, 50 μl) were injected intravenously in the search for an optimal dose. Clear transit curves were obtained with all doses and a blood flow index could easily be determined. The indocyanine green signal obtained with the bolus of 5 μl rapidly returned to baseline and interfered minimally with the haemoglobin and cytochrome oxidase signals. This dose was used in a second study to evaluate the reproducibility of the signal and the effect of hypercapnia. Two groups of rats received 7 repetitive boli of indocyanine green. In one group, 7% CO2 was added to the gas mixture before the second, fourth and sixth indocyanine green injection. Hypercapnia consistently caused a significant increase in blood flow index, cerebral haemoglobin concentration and O2-saturation. In the control group these variables remained stable in time. We conclude that monitoring of the transit of an indocyanine green bolus with multiwavelength near-infrared spectroscopy can be used to assess cerebral blood flow qualitatively in rats in combination with continuous monitoring of brain oxygenation. [Copyright &y& Elsevier]

The capacity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) to consume RuBP is a major limitation on the rate of net CO2 assimilation (A) in C3 and C4 plants. The pattern of Rubisco limitation differs between the two photosynthetic types, as shown by comparisons of temperature and CO2 responses of A and Rubisco activity from C3 and C4 species. In C3 species, Rubisco capacity is the primary limitation on A at light saturation and CO2 concentrations below the current atmospheric value of 37 Pa, particularly near the temperature optimum. Below 20 °C, C3 photosynthesis at 37 and 68 Pa is often limited by the capacity to regenerate phosphate for photophosphorylation. In C4 plants, the Rubisco capacity is equivalent to A below 18 °C, but exceeds the photosynthetic capacity above 25 °C, indicating that Rubisco is an important limitation at cool but not warm temperatures. A comparison of the catalytic efficiency of Rubisco (kcat in mol CO2 mol−1 Rubisco active sites s−1) from 17 C3 and C4 plants showed that Rubisco from C4 species, and C3 species originating in cool environments, had higher kcat than Rubisco from C3 species originating in warm environments. This indicates that Rubisco evolved to improve performance in the environment that plants normally experience. In C4 plants, and C3 species from cool environments, Rubisco often operates near CO2 saturation, so that increases in kcat would enhance A. In warm‐habitat C4 species, Rubisco often operates at CO2 concentrations below the Km for CO2. Because kcat and Km vary proportionally, the low kcat indicates that Rubisco has been modified in a manner that reduces Km and thus increases the affinity for CO2 in C3 species from warm climates. [ABSTRACT FROM PUBLISHER]

Using gas exchange, enzyme assays, and theoretical modeling of photosynthetic responses to light and CO2, we investigated whether decarbamylation of the active site of Rubisco at low CO2 and low light leads to a condition where the activation state of Rubisco directly limits the rate of net CO2 assimilation. Photosynthetic limitation by a reduction in the activation state of Rubisco would be indicated as a decline in the initial slope of the photosynthetic CO2 response relative to what is predicted using theoretical models. In bean ( Phaseolus vulgaris) and oat ( Avena sativa), we saw no discrepancy between predicted and observed initial slope values at 200 and 400 mbar O2, indicating no limitation by the carbamylation state of Rubisco. At 30 mbar O2 and light saturation, we also saw no discrepancy between predicted and observed initial slope values; however, at subsaturating light intensity, our observed initial slope values were less than the modeled initial slope values that corresponded to an RuBP regeneration limitation. Moreover, significant reduction of the Rubisco activation state occurred in both species at 30 mbar O2 and 30 μbar CO2. When the model was reprogrammed to account for observed levels of Rubisco deactivation, the predicted and measured initial slope values at low O2 and low PPFD were similar, indicating the reduction in carbamylation state accounted for the discrepancy. We interpret this as evidence for a direct limitation of the carbamylation state of Rubisco, probably because of a CO2 limitation for carbamate formation. This limitation was only observed at intercellular CO2 levels below what is encountered in vivo. At physiologically relevant CO2 levels in situ, the leaves maintained sufficient Rubisco activity to avoid cabamylation state limitations in the steady state. [ABSTRACT FROM AUTHOR]

Using 11 closely related grass species, we tested the capacity of physiological criteria to predict the growth response to elevated CO2 and to categorize the species with regard to their CO2 response. A growth analysis was conducted under productive conditions both at ambient (350 μmol mol-1) and elevated (700 μmol mol-1) CO2. The relative growth rate stimulation was regressed against each of the growth rate components measured at ambient CO2. Growth response to CO2 was positively correlated with specific leaf area (SLA, the leaf surface area per unit of leaf weight), leaf area ratio (the leaf area per unit of total plant dry weight) and negatively correlated with net assimilation rate and leaf nitrogen concentration, both per unit of leaf area. We suggest that SLA has a predominant role in these relationships. Different hypotheses are proposed and discussed in order to explain why species with low SLA are less responsive to elevated CO2. Neither biomass allocation, relative growth rate, shoot or root specific activities per unit of mass, nor chemical composition were significantly correlated with growth response to CO2. The four predictive criteria mentioned above coherently differentiate the five wild annual species (higher SLA, stronger growth response to CO2) from the four wild perennials. The two perennial crop species, with the highest SLA, were more responsive than the wild species. [ABSTRACT FROM AUTHOR]

The effect of elevated [CO2] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991-93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO2 response. Measurements of the canopy gas exchange (CO2 and water vapour) were made continuously from emergence until harvest. At an external [CO2] of 700 µmol mol-1 Maximum Canopy CO2 Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 µmol mol-1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991-93 were used, assuming adequate water supply and [CO2] at 350 and 700 µmol mol-1. For spring wheat the simulated responses (35-50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO2 response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO2 response can be largely explained by differences in weather conditions (especially temperature) between growing seasons. [ABSTRACT FROM AUTHOR]