Differential CO2 effect on primary carbon metabolism of flag leaves in durum wheat (Triticum durum Desf.)

An Analysis of the Mechanism About CO2 Enrichment Promoting Carbohydrate Metabolism in Cucumber (Cucumis sativus L.) Leaves

Elevated CO2 can affect the synthesis and distribution of photosynthetic assimilates. However, the carbohydrate metabolism molecular mechanism of cucumber leaves in response to CO2 enrichment is unclear. Therefore, it is of great significance to investigate the key functional regulatory genes in cucumber. In this study, the growth of cucumber leaves under different CO2 conditions was compared. The results showed that under CO2 enrichment, leaf area increased, the number of mesophyll cells increased, stomata enlarged, and more starch grains accumulated in the chloroplasts. Compared with the control, the starch and soluble sugar content of leaves were maximally increased by 194.1% and 55.94%, respectively; the activities of fructose-1,6-bisphosphatase (FBPase), ADPG pyrophosphorylase (AGPase), starch synthase (SSS), sucrose phosphate synthase (SPS), sucrose synthase (SS) and invertase (Inv) were maximally increased by 36.91%, 66.13%, 33.18%, 21.7%, 54.11%, and 46.01%, respectively. Through transcriptome analysis, a total of 1,582 differential expressed genes (DEGs) were identified, in which the starch and sucrose metabolism pathway was significantly enriched, and 23 genes of carbon metabolism were screened. Through metabolome analysis, a total of 22 differential accumulation metabolites (DAMs) were identified. Moreover, D-glucose and D(+)-glucose were significantly accumulated, showing upregulation 2.4-fold and 2.6-fold, respectively. Through combined analysis of transcriptome and metabolome, it was revealed that seven genes were highly related to D-glucose, and Csa6G153460 (AGPase), Csa5G612840 (β-glucosidase), and Csa4G420150 (4-α-glucanotransferase) were significantly correlated to the carbohydrate regulatory network. Furthermore, the mechanism of CO2 enrichment that promotes carbohydrate metabolism in leaves at the molecular level was revealed. This mechanism advances the development of the cell wall and leaf morphology by activating the expression of key genes and improving enzyme activity.

Optimizing oilseed rape growth: Exploring the effect of foliar biostimulants on the interplay among metabolism, phenology, and yield

The current agricultural system is in search of new strategies to achieve a more sustainable production while keeping or even increasing crop yield and quality. In this scenario, the application of biostimulants constitutes a potent solution. In the current study, the impact of a blue-green microalgal extract (MB) and a pig tissue hydrolysate (PTH) on rapeseed plants' development was characterized. Obtained results revealed a positive effect on yield parameters of plants treated with MB and, especially, PTH; this was associated to an improvement on the photosynthetic performance. Moreover, this study remarked the effects of biostimulants on plant phenology through their pivotal role in modulating developmental processes. More specifically, proteomic, metabolomic, and hormone content analyses revealed distinct alterations associated with the acceleration of phenology induced by biostimulant application. Additionally, some antioxidant enzymes and stress-related compounds were up-regulated upon MB and PTH treatments, indicating enhanced plant defense mechanisms in response to accelerated phenological transitions. Such findings highlight the intricate interplay between biostimulants and plant physiology, wherein biostimulants orchestrate rapid developmental changes, ultimately influencing growth dynamics. Altogether, the current study reveals that the application of both MB and PTH biostimulants promoted rapeseed plant phenology and productivity associated with an improvement in the photosynthetic machinery while boosting other physiological and molecular mechanisms.

Differential effects of elevated CO2 on awn and glume metabolism in durum wheat (Triticum durum)

While the effect of CO2 enrichment on wheat (Triticum spp.) photosynthesis, nitrogen content or yield has been well-studied, the impact of elevated CO2 on metabolic pathways in organs other than leaves is poorly documented. In particular, glumes and awns, which may refix CO2 respired by developing grains and be naturally exposed to higher-than-ambient CO2 mole fraction, could show specific responses to elevated CO2 . Here, we took advantage of a free-air CO2 enrichment experiment and performed multilevel analyses, including metabolomics, ionomics, proteomics, major hormones and isotopes in Triticum durum . While in leaves, elevated CO2 tended to accelerate amino acid metabolism with many significantly affected metabolites, the effect on glumes and awns metabolites was modest. There was a lower content in compounds of the polyamine pathway (along with uracile and allantoin) under elevated CO2 , suggesting a change in secondary N metabolism. Also, cytokinin metabolism appeared to be significantly affected under elevated CO2 . Despite this, elevated CO2 did not affect the final composition of awn and glume organic matter, with the same content in carbon, nitrogen and other elements. We conclude that elevated CO2 mostly impacts on leaf metabolism but has little effect in awns and glumes, including their composition at maturity.

Elevated atmospheric CO2 concentration mitigates salt damages to safflower: Evidence from physiological and biochemical examinations

The physiological and biochemical responses of salt-stressed safflower to elevated CO2 remain inadequately known. This study investigated the interactive effects of high CO2 concentration (700 ± 50 vs. 400 ± 50 μmol mol-1) and salinity stress levels (0.4, 6, and 12 dS m-1, NaCl) on growth and physiological properties of four safflower (Carthamus tinctorius L.) genotypes, under open chamber conditions. Results showed that the effects of CO2 on biomass of shoot and grains depend on salt stress and plant genotype. Elevated CO2 conditions increased shoot dry weight under moderate salinity stress and decreased it under severe stress. The increased CO2 concentration also increased the safflower genotypes' relative water content and their K+/Na + concentrations. Also enriched CO2 increased total carotenoid levels in safflower genotypes and improved membrane stability index by reducing H2O2 levels. In addition, increased CO2 level led to an increase in seed oil content, under both saline and non-saline conditions. This effect was particularly pronounced under severe saline conditions. Under conditions of high CO2 and salinity, the Koseh genotype exhibited higher grain weight and seed oil content than other genotypes. This advantage is due to the higher relative water content, maximum quantum efficiency of photosystem II (Fv/Fm), and K+/Na+, as well as the lower Na+ and H2O2 concentrations. Results indicate that the high CO2 level mitigated the destructive effect of salinity on safflower growth by reducing Na + uptake and increasing the Fv/Fm, total soluble carbohydrates, and membrane stability index. This finding can be used in safflower breeding programs to develop cultivars that can thrive in arid regions with changing climatic conditions.

H2 S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen-deficient soybeans

Hydrogen sulfide (H₂ S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H₂ S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H₂ S drives photosynthetic C fixation, utilisation, and accumulation in soybean-rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N-fixation performance were considerably improved owing to H₂ S and rhizobia. Furthermore, H₂ S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H₂ S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H₂ S and rhizobia on primary metabolism and C-N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H₂ S synergy with rhizobia inspired complex primary metabolism and C-N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans.

Physiological and transcriptome analysis of response of soybean (Glycine max) to cadmium stress under elevated CO2 concentration

The continuous accumulation of Cd has long-lasting detrimental effects on plant growth and food safety. Although elevated CO₂ concentration (EC) has been reported to reduce Cd accumulation and toxicity in plants, evidence on the functions of elevated CO₂ concentration and its mechanisms in the possible alleviation of Cd toxicity in soybean are limited. Here, we used physiological and biochemical methods together with transcriptomic comparison to explore the effects of EC on Cd-stressed soybean. Under Cd stress, EC significantly increased the weight of roots and leaves, promoted the accumulations of proline, soluble sugars, and flavonoid. In addition, the enhancement of GSH activity and GST gene expressions promoted Cd detoxification. These defensive mechanisms reduced the contents of Cd²⁺, MDA, and H₂O₂ in soybean leaves. The up-regulation of genes encoding phytochelatin synthase, MTPs, NRAMP, and vacuoles protein storage might play vital roles in the transportation and compartmentalization process of Cd. The MAPK and some transcription factors such as bHLH, AP2/ERF, and WRKY showed changed expressions and might be engaged in mediation of stress response. These findings provide a boarder view on the regulatory mechanism of EC on Cd stress and provide numerous potential target genes for future engineering of Cd-tolerant cultivars in soybean breeding programs under climate changes scenarios.

Differential Effect of Free-Air CO2 Enrichment (FACE) in Different Organs and Growth Stages of Two Cultivars of Durum Wheat

Wheat is a target crop within the food security context. The responses of wheat plants under elevated concentrations of CO₂ (e[CO₂]) have been previously studied; however, few of these studies have evaluated several organs at different phenological stages simultaneously under free-air CO₂ enrichment (FACE) conditions. The main objective of this study was to evaluate the effect of e[CO₂] in two cultivars of wheat (Triumph and Norin), analyzed at three phenological stages (elongation, anthesis, and maturation) and in different organs at each stage, under FACE conditions. Agronomic, biomass, physiological, and carbon (C) and nitrogen (N) dynamics were examined in both ambient CO₂ (a[CO₂]) fixed at 415 µmol mol^-1 CO₂ and e[CO₂] at 550 µmol mol^-1 CO₂. We found minimal effect of e[CO₂] compared to a[CO₂] on agronomic and biomass parameters. Also, while exposure to 550 µmol mol^-1 CO₂ increased the photosynthetic rate of CO₂ assimilation (An), the current study showed a diminishment in the maximum carboxylation (V_c,max) and maximum electron transport (J_max) under e[CO₂] conditions compared to a[CO₂] at physiological level in both cultivars. However, even if no significant differences were detected between cultivars on photosynthetic machinery, differential responses between cultivars were detected in C and N dynamics at e[CO₂]. Triumph showed starch accumulation in most organs during anthesis and maturation, but a decline in N content was observed. Contrastingly, in Norin, a decrease in starch content during the three stages and an increase in N content was observed. The amino acid content decreased in grain and shells at maturation in both cultivars, which might indicate a minimal translocation from source to sink organs. These results suggest a greater acclimation to e[CO₂] enrichment in Triumph than Norin, because both the elongation stage and e[CO₂] modified the source-sink relationship. According to the differences between cultivars, future studies should be performed to test genetic variation under FACE technology and explore the potential of cultivars to cope with projected climate scenarios.

Wheat Omics: Advancements and Opportunities

Plant omics, which includes genomics, transcriptomics, metabolomics and proteomics, has played a remarkable role in the discovery of new genes and biomolecules that can be deployed for crop improvement. In wheat, great insights have been gleaned from the utilization of diverse omics approaches for both qualitative and quantitative traits. Especially, a combination of omics approaches has led to significant advances in gene discovery and pathway investigations and in deciphering the essential components of stress responses and yields. Recently, a Wheat Omics database has been developed for wheat which could be used by scientists for further accelerating functional genomics studies. In this review, we have discussed various omics technologies and platforms that have been used in wheat to enhance the understanding of the stress biology of the crop and the molecular mechanisms underlying stress tolerance.

Could ammonium nutrition increase plant C-sink strength under elevated CO2 conditions?

Atmospheric carbon dioxide (CO₂) is increasing, and this affects plant photosynthesis and biomass production. Under elevated CO₂ conditions (eCO₂), plants need to cope with an unbalanced carbon-to-nitrogen ratio (C/N) due to a limited C sink strength and/or the reported constrains in leaf N. Here, we present a physiological and metabolic analysis of ammonium (NH₄⁺)-tolerant pea plants (Pisum sativum L., cv. snap pea) grown hydroponically with moderate or high NH₄⁺ concentrations (2.5 or 10 mM), and under two atmospheric CO₂ concentrations (400 and 800 ppm). We found that the photosynthetic efficiency of the NH₄⁺ tolerant pea plants remain intact under eCO₂ thanks to the capacity of the plants to maintain the foliar N status (N content and total soluble proteins), and the higher C-skeleton requirements for NH₄⁺ assimilation. The capacity of pea plants grown at 800 ppm to promote the C allocation into mobile pools of sugar (mainly sucrose and glucose) instead of starch contributed to balancing plant C/N. Our results also support previous observations: plants exposed to eCO₂ and NH₄⁺ nutrition can increase of stomatal conductance. Considering the C and N source-sink balance of our plants, we call for exploring a novel trait, combining NH₄⁺ tolerant plants with a proper NH₄⁺ nutrition management, as a way for a better exploitation of eCO₂ in C3 crops.

Transcriptomic, proteomic, and physiological studies reveal key players in wheat nitrogen use efficiency under both high and low nitrogen supply

The effective use of available nitrogen (N) to improve crop grain yields provides an important strategy to reduce environmental N pollution and promote sustainable agriculture. However, little is known about the common genetic basis of N use efficiency (NUE) at varying N availability. Two wheat (Triticum aestivum L.) cultivars were grown in the field with high, moderate, and low N supply. Cultivar Zhoumai 27 outperformed Aikang 58 independent of the N supply and showed improved growth, canopy leaf area index, flag leaf surface area, grain number, and yield, and enhanced NUE due to both higher N uptake and utilization efficiency. Further, transcriptome and proteome analyses were performed using flag leaves that provide assimilates for grain growth. The results showed that many genes or proteins that are up- or down-regulated under all N regimes are associated with N and carbon metabolism and transport. This was reinforced by cultivar differences in photosynthesis, assimilate phloem transport, and grain protein/starch yield. Overall, our study establishes that improving NUE at both high and low N supply requires distinct adjustments in leaf metabolism and assimilate partitioning. Identified key genes/proteins may individually or concurrently regulate NUE and are promising targets for maximizing crop NUE irrespective of the N supply.

Recent Advances in Carbon and Nitrogen Metabolism in C3 Plants

C and N are the most important essential elements constituting organic compounds in plants. The shoots and roots depend on each other by exchanging C and N through the xylem and phloem transport systems. Complex mechanisms regulate C and N metabolism to optimize plant growth, agricultural crop production, and maintenance of the agroecosystem. In this paper, we cover the recent advances in understanding C and N metabolism, regulation, and transport in plants, as well as their underlying molecular mechanisms. Special emphasis is given to the mechanisms of starch metabolism in plastids and the changes in responses to environmental stress that were previously overlooked, since these changes provide an essential store of C that fuels plant metabolism and growth. We present general insights into the system biology approaches that have expanded our understanding of core biological questions related to C and N metabolism. Finally, this review synthesizes recent advances in our understanding of the trade-off concept that links C and N status to the plant's response to microorganisms.

Elevated CO2 has concurrent effects on leaf and grain metabolism but minimal effects on yield in wheat

While the general effect of CO2 enrichment on photosynthesis, stomatal conductance, N content, and yield has been documented, there is still some uncertainty as to whether there are interactive effects between CO2 enrichment and other factors, such as temperature, geographical location, water availability, and cultivar. In addition, the metabolic coordination between leaves and grains, which is crucial for crop responsiveness to elevated CO2, has never been examined closely. Here, we address these two aspects by multi-level analyses of data from several free-air CO2 enrichment experiments conducted in five different countries. There was little effect of elevated CO2 on yield (except in the USA), likely due to photosynthetic capacity acclimation, as reflected by protein profiles. In addition, there was a significant decrease in leaf amino acids (threonine) and macroelements (e.g. K) at elevated CO2, while other elements, such as Mg or S, increased. Despite the non-significant effect of CO2 enrichment on yield, grains appeared to be significantly depleted in N (as expected), but also in threonine, the S-containing amino acid methionine, and Mg. Overall, our results suggest a strong detrimental effect of CO2 enrichment on nutrient availability and remobilization from leaves to grains.

Differential Flag Leaf and Ear Photosynthetic Performance Under Elevated (CO2) Conditions During Grain Filling Period in Durum Wheat

Elevated concentrations of CO₂ (CO₂) in plants with C₃ photosynthesis metabolism, such as wheat, stimulate photosynthetic rates. However, photosynthesis tends to decrease as a function of exposure to high (CO₂) due to down-regulation of the photosynthetic machinery, and this phenomenon is defined as photosynthetic acclimation. Considerable efforts are currently done to determine the effect of photosynthetic tissues, such us spike, in grain filling. There is good evidence that the contribution of ears to grain filling may be important not only under good agronomic conditions but also under high (CO₂). The main objective of this study was to compare photoassimilate production and energy metabolism between flag leaves and glumes as part of ears of wheat (Triticum turgidum L. subsp. durum cv. Amilcar) plants exposed to ambient [a(CO₂)] and elevated [e(CO₂)] (CO₂) (400 and 700 μmol mol^-1, respectively). Elevated CO₂ had a differential effect on the responses of flag leaves and ears. The ears showed higher gross photosynthesis and respiration rates compared to the flag leaves. The higher ear carbohydrate content and respiration rates contribute to increase the grain dry mass. Our results support the concept that acclimation of photosynthesis to e(CO₂) is driven by sugar accumulation, reduction in N concentrations and repression of genes related to photosynthesis, glycolysis and the tricarboxylic acid cycle, and that these were more marked in glumes than leaves. Further, important differences are described on responsiveness of flag leaves and ears to e(CO₂) on genes linked with carbon and nitrogen metabolism. These findings provide information about the impact of e(CO₂) on ear development during the grain filling stage and are significant for understanding the effects of increasing (CO₂) on crop yield.

Metabolomics Provides Valuable Insight for the Study of Durum Wheat: A Review

Metabolomics is increasingly being applied in various fields offering a highly informative tool for high-throughput diagnostics. However, in plant sciences, metabolomics is underused, even though plant studies are relatively easy and cheap when compared to those on humans and animals. Despite their importance for human nutrition, cereals, and especially wheat, remain understudied from a metabolomics point of view. The metabolomics of durum wheat has been essentially neglected, although its genetic structure allows the inference of common mechanisms that can be extended to other wheat and cereal species. This review covers the present achievements in durum wheat metabolomics highlighting the connections with the metabolomics of other cereal species (especially bread wheat). We discuss the metabolomics data from various studies and their relationships to other "-omics" sciences, in terms of wheat genetics, abiotic and biotic stresses, beneficial microbes, and the characterization and use of durum wheat as feed, food, and food ingredient.

C and N metabolism in barley leaves and peduncles modulates responsiveness to changing CO2

Balancing of leaf carbohydrates is a key process for maximising crop performance in elevated CO2 environments. With the aim of testing the role of the carbon sink-source relationship under different CO2 conditions, we performed two experiments with two barley genotypes (Harrington and RCSL-89) exposed to changing CO2. In Experiment 1, the genotypes were exposed to 400 and 700 ppm CO2. Elevated CO2 induced photosynthetic acclimation in Harrington that was linked with the depletion of Rubisco protein. In contrast, a higher peduncle carbohydrate-storage capacity in RSCL-89 was associated with a better balance of leaf carbohydrates that could help to maximize the photosynthetic capacity under elevated CO2. In Experiment 2, plants that were grown at 400 ppm or 700 ppm CO2 for 5 weeks were switched to 700 ppm or 400 ppm CO2, respectively. Raising CO2 to 700 ppm increased photosynthetic rates with a reduction in leaf carbohydrate content and an improvement in N assimilation. The increase in nitrate content was associated with up-regulation of genes of protein transcripts of photosynthesis and N assimilation that favoured plant performance under elevated CO2. Finally, decreasing the CO2 from 700 ppm to 400 ppm revealed that both stomatal closure and inhibited expression of light-harvesting proteins negatively affected photosynthetic performance and plant growth.

New insights into the cellular mechanisms of plant growth at elevated atmospheric carbon dioxide concentrations

Rising atmospheric carbon dioxide concentration ([CO₂ ]) significantly influences plant growth, development, and biomass. Increased photosynthesis rate, together with lower stomatal conductance, has been identified as the key factors that stimulate plant growth at elevated [CO₂ ] (e[CO₂ ]). However, variations in photosynthesis and stomatal conductance alone cannot fully explain the dynamic changes in plant growth. Stimulation of photosynthesis at e[CO₂ ] is always associated with post-photosynthetic secondary metabolic processes that include carbon and nitrogen metabolism, cell cycle functions, and hormonal regulation. Most studies have focused on photosynthesis and stomatal conductance in response to e[CO₂ ], despite the emerging evidence of e[CO₂ ]'s role in moderating secondary metabolism in plants. In this review, we briefly discuss the effects of e[CO₂ ] on photosynthesis and stomatal conductance and then focus on the changes in other cellular mechanisms and growth processes at e[CO₂ ] in relation to plant growth and development. Finally, knowledge gaps in understanding plant growth responses to e[CO₂ ] have been identified with the aim of improving crop productivity under a CO₂ rich atmosphere.

Effects of Elevated Atmospheric CO2 on Respiratory Rates in Mature Leaves of Two Rice Cultivars Grown at a Free-Air CO2 Enrichment Site and Analyses of the Underlying Mechanisms

Respiratory CO2 efflux and O2 uptake rates in leaves change in response to the growth CO2 concentration ([CO2]). The degrees of change vary depending on the responses of cellular processes such as nitrogen (N) assimilation and accumulation of organic acids to growth [CO2]. However, the underlying mechanisms remain unclear. Here, we examined the respiratory characteristics of mature leaves of two rice varieties with different yield capacities at different growth stages under ambient and elevated [CO2] conditions at a free-air CO2 enrichment site. We also examined the effect of increased water temperature on leaf respiration. We measured the rates of CO2 efflux and O2 uptake, and determined N contents, primary metabolite contents and maximal activities of respiratory enzymes. The leaf CO2 efflux rates decreased in plants grown at elevated [CO2] in both varieties, and were higher in high-yielding Takanari than in Koshihikari. The leaf O2 uptake rates showed little change with respect to growth [CO2] and variety. The increased water temperature did not significantly affect the CO2 efflux and O2 uptake rates. The N and amino acid contents were significantly higher in Takanari than in Koshihikari. The enhanced N assimilation in Takanari may have consumed more respiratory NADH, leading to higher CO2 efflux rates. In Koshihikari, the ratio of tricarboxylic acid (TCA) cycle intermediates changed and maximal activities of enzymes in the TCA cycle decreased at elevated [CO2]. Therefore, the decreased rates of CO2 efflux in Koshihikari may be due to the decreased activities of TCA cycle enzymes at elevated [CO2].

Melatonin alleviates low PS I-limited carbon assimilation under elevated CO2 and enhances the cold tolerance of offspring in chlorophyll b-deficient mutant wheat

Melatonin is involved in the regulation of carbohydrate metabolism and induction of cold tolerance in plants. The objective of this study was to investigate the roles of melatonin in modulation of carbon assimilation of wild-type wheat and the Chl b-deficient mutant ANK32B in response to elevated CO₂ concentration ([CO₂ ]) and the transgenerational effects of application of exogenous melatonin (hereafter identified as melatonin priming) on the cold tolerance in offspring. The results showed that the melatonin priming enhanced the carbon assimilation in ANK32B under elevated [CO₂ ], via boosting the activities of ATPase and sucrose synthesis and maintaining a relatively higher level of total chlorophyll concentration in leaves. In addition, melatonin priming in maternal plants at grain filling promoted the seed germination in offspring by accelerating the starch degradation and improved the cold tolerance of seedlings through activating the antioxidant enzymes and enhancing the photosynthetic electron transport efficiency. These findings suggest the important roles of melatonin in plant response to future climate change, indicating that the melatonin priming at grain filling in maternal plants could be an effective approach to improve cold tolerance of wheat offspring at seedling stage.

Leaf day respiration: low CO2 flux but high significance for metabolism and carbon balance

Contents 986 I. 987 II. 987 III. 988 IV. 991 V. 992 VI. 995 VII. 997 VIII. 998 References 998 SUMMARY: It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low-flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO₂ and thus impacts on plant carbon and nitrogen balances. However, for a long time, uncertainties have remained as to whether techniques used to measure day respiratory efflux were valid and whether day respiration responded to environmental gaseous conditions. In the past few years, significant advances have been made using carbon isotopes, 'omics' analyses and surveys of respiration rates in mesocosms or ecosystems. There is substantial evidence that day respiration should be viewed as a highly dynamic metabolic pathway that interacts with photosynthesis and photorespiration and responds to atmospheric CO₂ mole fraction. The view of leaf day respiration as a constant and/or negligible parameter of net carbon exchange is now outdated and it should now be regarded as a central actor of plant carbon-use efficiency.

Release of resource constraints allows greater carbon allocation to secondary metabolites and storage in winter wheat

The atmospheric CO₂ concentration ([CO₂ ]) is rapidly increasing, and this may have substantial impact on how plants allocate metabolic resources. A thorough understanding of allocation priorities can be achieved by modifying [CO₂ ] over a large gradient, including low [CO₂ ], thereby altering plant carbon (C) availability. Such information is of critical importance for understanding plant responses to global environmental change. We quantified the percentage of daytime whole-plant net assimilation (A) allocated to night-time respiration (R), structural growth (SG), nonstructural carbohydrates (NSC) and secondary metabolites (SMs) during 8 weeks of vegetative growth in winter wheat (Triticum aestivum) growing at low, ambient and elevated [CO₂ ] (170, 390 and 680 ppm). R/A remained relatively constant over a large gradient of [CO₂ ]. However, with increasing C availability, the fraction of assimilation allocated to biomass (SG + NSC + SMs), in particular NSC and SMs, increased. At low [CO₂ ], biomass and NSC increased in leaves but decreased in stems and roots, which may help plants achieve a functional equilibrium, that is, overcome the most severe resource limitation. These results reveal that increasing C availability from rising [CO₂ ] releases allocation constraints, thereby allowing greater investment into long-term survival in the form of NSC and SMs.

Rising CO2 from historical concentrations enhances the physiological performance of Brassica napus seedlings under optimal water supply but not under reduced water availability

The productivity of many important crops is significantly threatened by water shortage, and the elevated atmospheric CO₂ can significantly interact with physiological processes and crop responses to drought. We examined the effects of three different CO₂ concentrations (historical ~300 ppm, ambient ~400 ppm and elevated ~700 ppm) on physiological traits of oilseed rape (Brassica napus L.) seedlings subjected to well-watered and reduced water availability. Our data show (1) that, as expected, increasing CO₂ level positively modulates leaf photosynthetic traits, leaf water-use efficiency and growth under non-stressed conditions, although a pronounced acclimation of photosynthesis to elevated CO₂ occurred; (2) that the predicted elevated CO₂ concentration does not reduce total evapotranspiration under drought when compared with present (400 ppm) and historical (300 ppm) concentrations because of a larger leaf area that does not buffer transpiration; and (3) that accordingly, the physiological traits analysed decreased similarly under stress for all CO₂ concentrations. Our data support the hypothesis that increasing CO₂ concentrations may not significantly counteract the negative effect of increasing drought intensity on Brassica napus performance.

Wheat ear carbon assimilation and nitrogen remobilization contribute significantly to grain yield

The role of wheat ears as a source of nitrogen (N) and carbon (C) in the grain filling process has barely been studied. To resolve this question, five wheat genotypes were labeled with ¹⁵ N-enriched nutrient solution. N remobilization and absorption were estimated via the nitrogen isotope composition of total organic matter and Rubisco. Gas exchange analyses showed that ear photosynthesis contributed substantially to grain filling in spite of the great loss of C due to respiration. Of the total kernel N, 64.7% was derived from the N acquired between sowing and anthesis, while the remaining 35.3% was derived from the N acquired between anthesis and maturity. In addition, 1.87 times more N was remobilized to the developing kernel from the ear than from the flag leaf. The higher yielding genotypes showed an increased N remobilization to the kernel compared to the lower yielding genotypes. In addition, the higher yielding genotypes remobilized more N from the ears to the kernel than the lower yielding genotypes, while the lower yielding genotypes remobilized more N from the flag leaf to the kernel. Therefore, the ears contribute significantly toward fulfilling C and N demands during grain filling.