Effects of elevated atmospheric CO2 on grain quality of wheat

Wheat (Triticum aestivum L.) is one of the most important agricultural crops worldwide. Due to its high content of starch and unique gluten proteins, wheat grain is used for many food and non-food applications. Although grain quality is an important topic for food and feed as well as industrial processing, the consequences of future increases in atmospheric carbon dioxide (CO₂) concentrations on quality parameters such as nutritional and bread-making rheological properties are still unclear. Wheat productivity increases under CO₂ enrichment. Concomitantly, the chemical composition of vegetative plant parts is often changed and grain quality is altered. In particular, the decrease in grain protein concentration and changes in protein composition may have serious economic and health implications. Additionally, CO₂ enrichment affects amino acid composition and the concentrations of macro- and micro-elements. However, experimental results are often inconsistent. The present review summarises the results from numerous CO₂ enrichment experiments using different exposure techniques in order to quantify the potential impacts of projected atmospheric CO₂ levels on wheat grain yield and on aspects of grain composition relevant to processing and human nutrition.     

Intra-specific variation of wheat grain quality in response to elevated [CO2] at two sowing times under rain-fed and irrigation treatments

In order to investigate the intra-specific variation of wheat grain quality response to elevated atmospheric CO₂ concentration (e[CO₂]), eight wheat (Triticum aestivum L.)cultivars were grown at two CO₂ concentrations ([CO₂]) (current atmospheric, 389 CO₂ μmol mol⁻¹vs. e[CO₂], FACE (Free-Air CO₂ Enrichment), 550  ±  10% CO₂ μmol mol⁻¹), at two water levels (rain-fed vs. irrigated) and at two times of sowing (TOS₁, vs. TOS₂). The TOS treatment was mainly imposed to understand whether e[CO₂] could modify the effects of timing of higher grain filling temperatures on grain quality. When plants were grown at TOS₁, TKW (thousand kernel weight), grain test weight, hardness index, P, Ca, Na and phytate were not significantly changed under e[CO₂]. On the other hand, e[CO₂] increased TKW (16%), hardness index (9%), kernel diameter (6%), test weight (2%) but decreased grain protein (10%) and grain phytate (11%) at TOS₂. In regard to grain Zn, Mn and Cu concentrations and some flour rheological properties, cultivar specific responses to e[CO₂] were observed at both sowing times. Observed genetic variability in response to e[CO₂] in terms of grain minerals and flour rheological properties could be easily incorporated into future wheat breeding programs to enable adaptation to climate change.     

Wheat grain quality under increasing atmospheric CO2 concentrations in a semi-arid cropping system

We investigated wheat (Triticum aestivum) grain quality under Free Air CO₂ Enrichment (FACE) of 550 ± 10% CO₂ μmol mol⁻¹. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO₂ increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO₂], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO₂] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO₂] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO₂] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO₂] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO₂] effects may be moderated. Reduced phytate concentrations at e[CO₂] may improve bioavailability of Fe and Zn in wheat grain.     

Wheat grain quality under increasing atmospheric CO2 concentrations in a semi-arid cropping system

We investigated wheat (Triticum aestivum) grain quality under Free Air CO₂ Enrichment (FACE) of 550 ± 10% CO₂ μmol mol⁻¹. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO₂ increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO₂], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO₂] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO₂] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO₂] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO₂] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO₂] effects may be moderated. Reduced phytate concentrations at e[CO₂] may improve bioavailability of Fe and Zn in wheat grain.     

Atmospheric CO2 enrichment changes the wheat grain proteome

Spring wheat (Triticum aestivum L. cv. Triso) was grown in a free-air CO₂ enrichment (FACE) field experiment in order to gain information on CO₂-induced effects on grain composition and quality at maturity. A proteome analysis was performed using two-dimensional gel electrophoresis (2-DE) and protein identification was done with mass spectrometry (MALDI-TOF MS). In elevated CO₂ (526 μl l⁻¹), an increase of 13.5% in grain yield was observed relative to 375 μl l⁻¹ at a low level of significance (P = 0.528). Total grain protein concentration was decreased by 3.5% at a high level of statistical significance. Most importantly, a number of statistically significant changes within the grain proteome were observed, as the levels of 32 proteins were affected by elevated CO₂: 16 proteins were up-regulated and 16 were down-regulated. Our experiment demonstrates that high-CO₂ can markedly affect the proteome of mature wheat grain. The potential role of the proteins, changed in response to CO₂ enrichment, is discussed as some may affect grain quality. For the task of selecting cultivars resistant to CO₂-induced quality loss, we propose to consider the proteins affected by elevated CO₂ identified in this work here.     

Wheat (Triticum aestivum L.) grain proteome response to elevated [CO2] varies between genotypes

The impact of rising carbon dioxide concentration ([CO₂]) in the atmosphere on wheat grain protein concentration and proteome was investigated in this study. Wheat genotypes (H45, SB003, SB062 and Yitpi) were grown in the Australian Grains Free-Air CO₂ Enrichment (AGFACE) facility, Horsham, Victoria, Australia under ambient [CO₂] (a[CO₂], 391 μmol mol⁻¹) and elevated [CO₂] (e[CO₂], 550 ± 20 μmol mol⁻¹). Grain yield and grain protein concentration were measured. Global grain proteome comparison was carried out using stable isotope dimethyl labelling followed by liquid chromatography - mass spectrometry (LC-MS/MS). Grain yield was significantly increased at e[CO₂], whereas protein concentration was significantly decreased and responses varied between genotypes. Proteome-wide analysis revealed that protein composition was also altered under e[CO₂]. Grain protein concentration and composition of SB003 was very responsive to e[CO₂]. Mainly storage proteins were decreased at e[CO₂] and the responses varied between genotypes. These findings suggest that e[CO₂] may have a major impact on grain protein quality and thus bread quality and human and animal nutrition. Further, these findings suggest that [CO₂] insensitive cultivars can be identified for grain quality improvement under changing climate.     

CO2 Enrichment Effects on Forage and Grain Nitrogen Content of Pasture and Cereal Plants

SUMMARY

Increasing atmospheric CO₂ concentrations [CO₂] have the potential to enhance growth and yield of agricultural plants. Con-comitantly plants grown under high [CO₂] show significant changes of the chemical composition of their foliage and of other plant parts. Particularly, high [CO₂] result in a decrease of plant nitrogen (N) concentration, which may have serious consequences for crop quality. This presentation summarizes the results of a variety of CO₂ enrichment studies with pasture plants (Lolium spp., Trifolium repens) and cereal species (Triticum aestivum, Hordeum vulgare) which were conducted at our laboratory under different growth and CO₂ exposure conditions ranging from controlled environment studies to investigations under free air carbon dioxide enrichment (FACE). With the exception of clover in all experiments a CO₂-induced decline of forage and grain N concentration was observed. The magnitude of this reduction differed between species, cultivars, management conditions (N fertilization) and CO₂ exposure conditions. No unambiguous evidence was obtained whether N fertilization can contribute to meet the quality requirements for cereals and grass monocultures with respect to tissue N concentrations in a future high-CO₂ world. As shown in the FACE experiments current application rates of N fertilizers are inadequate to achieve quality standards.     

Yield dilution of grain Zn in wheat grown in open-top chamber experiments with elevated CO2 and O3 exposure

Wheat (Triticum aestivum L.) grain Zn data from six open-top chamber experiments performed in south-west Sweden were combined to study the relationship between Zn accumulation and grain yield, grain protein, and yield components. Treatments included, in addition to open-top chamber controls, elevated CO₂, elevated O₃, combined CO₂ and O₃ exposure, combined elevated CO₂ and supplemental irrigation, supplemental irrigation, and ambient air comparison plots. The grain Zn concentration was strongly correlated with grain protein (R² = 0.90) over the range of the experimental treatments, representing non-soil factors. A significant yield dilution effect was found for Zn. For a 10% increase in grain yield, Zn yield was increased by 6.8% on average. Effects on Zn yield correlated strongly with effects on grain protein yield, with a slope close to unity, showing that yield dilution effects for grain Zn and grain protein were similar. Treatment effects on grain Zn concentration were related to effects on grain weight (P < 0.01) and grain number (P < 0.05), but not to harvest index. It was concluded that yield stimulation caused by rising CO₂ concentrations is likely to lead to reduced Zn concentrations of wheat grain, thus reducing the nutritional quality.     

Effect of free-air CO2 enrichment on the storage of carbohydrate fixed at different stages in rice (Oryza sativa L.)

Increasing global atmospheric CO₂ concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO₂ (AMB) or free-air CO₂-enrichment (FACE) at CO₂ concentrations ranged from 275 to 365 μmol mol⁻¹ above AMB. We supplied ¹³CO₂ to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with ¹³C at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem ¹³C content. Furthermore, there were no differences between treatments in whole-plant ¹³C contents at heading and grain maturity. In contrast, plants supplied with ¹³C at the grain-filling stage had more ¹³C in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO₂ enrichment might be effectively stored in the grains. Furthermore, regardless of when the ¹³C was supplied, plants had more ¹³C in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO₂ enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains.     

The impact of free-air CO2 enrichment (FACE) and nitrogen supply on grain quality of rice

Because CO₂ is needed for plant photosynthesis, the increase in atmospheric CO₂ concentration ([CO₂]) has the potential to enhance the growth and yield of rice (Oryza sativa L.), but little is known regarding the impact of elevated [CO₂] on grain quality of rice, especially under different N availability. In order to investigate the interactive effects of [CO₂] and N supply on rice quality, we conducted a free-air CO₂ enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001–2003. A long-duration rice japonica with large panicle (cv. Wuxiangging 14) was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] under three levels of N: low (LN, 15 g N m²), medium (MN, 25 g N m²) and high N (HN, 35 g N m² (2002, 2003)). The MN level was similar to that recommended to local farmers. FACE significant increased rough (+12.8%), brown (+13.2%) and milled rice yield (+10.7%), while markedly reducing head rice yield (−13.3%); FACE caused serious deterioration of processing suitability (milled rice percentage −2.0%; head rice percentage −23.5%) and appearance quality (chalky grain percentage +16.9%; chalkiness degree +28.3%) drastically; the nutritive value of grains was also negatively influenced by FACE due to a reduction in protein (−6.0%) and Cu content (−20.0%) in milled rice. By contrast, FACE resulted in better eating/cooking quality (amylose content −3.8%; peak viscosity +4.5%, breakdown +2.9%, setback −27.5%). These changes in grain quality revealed that hardness of grain decreased with elevated [CO₂] while cohesiveness and resilience increased when cooked. Overall, N supply had significant influence on rice yield with maximum value occurring at MN, whereas grain quality was less responsive to the N supply, showing trends of better appearance and eating/cooking quality for LN or MN-crops as compared with HN-crops. For most cases, no [CO₂] × N interaction was detected for yield and quality parameters. These data suggested that the current recommended rates of N fertilization for rice production should not be modified under projected future [CO₂] levels, at least for the similar conditions of this experiment.     

Effects of atmospheric CO2 enrichment on biomass,yield and low molecular weight metabolites in wheat grain

Spring wheat (Triticum aestivum L.) was grown in a free-air carbon dioxide (CO₂) enrichment (FACE) field experiment. Grain and biomass yield and its components were determined at maturity and the grain metabolome was analysed by gas chromatography-mass spectrometry (GC–MS). Elevated CO₂ (537 versus 409 μl l⁻¹) increased biomass production except for leaves. In total, levels of 16 grain metabolites were decreased and four were increased. CO₂ enrichment resulted in significant decreases of amino acids such as o-acetyl-L-homoserine, leucine, arginine, L-homoserine and the group of ornithine, arginine and citrulline and negative trends for norleucine, L-aspartate, proline, L-cysteine and tyrosine. The amines D/L-diaminopimelate and alpha-ketoaminobutyrate and the polyamine putrescine were significantly decreased. In contrast, the polyamine spermidine tended to increase under elevated CO₂. Among sugars and sugar derivatives, ribose-5-P was significantly increased, while gluconate-6-P was decreased. There were also negative CO₂-induced effects on sugar alcohols: significant for glycerol-2-P (P = 0.008) and almost significant for myo-inositol-P (P = 0.066). In contrast, organic acids such as pyruvate and glucuronic acid were significantly increased. Overall, the N-rich metabolites especially were reduced. CO₂ enrichment can markedly affect the physiology and metabolome of mature grains which may in turn lead to changes in nutritional status.     

Quality (End-Use) Improvement in Wheat

Abstract

Wheat provides nutrients and the raw materials for industrialized food production. Recent global economic trends and increases in urban population growth have led to an increased demand for wheat-based convenience foods (fast, ready-to-eat, frozen foods, etc.) and for new wheat-based products. These factors have resulted in a greater emphasis than ever on the end-use quality of wheat. This paper reviews grain compositional aspects influencing the processing and quality attributes of the main foods produced with wheat, as well as the breeding strategies and methodologies used to achieve germplasm with desirable end-use quality. Common wheat (Triticum aestivum) is used in bread (leavened, flat, and steamed), noodles, biscuits, and cakes. Durum wheat (T. turgidum L. var. durum) is used globally in alimentary pasta and regional foods (flat breads, couscous, and burghoul) in North Africa and West Asia. Grain characteristics (grain hardness, protein content/quality, enzymatic activity, etc.) play a moderate to important role in the processing and end-use quality of wheat-based products. Among these, gluten strength and extensibility, which are determined by glutenin (HMW and LMW) and gliadin composition, are two of the main factors that determine quality. The complex and generally additive nature of inheritance of most quality traits has led to the development of several indirect tests used in early and advanced generations to increase the frequency of high yielding lines with desirable quality attributes. Additionally, characterization of HMW and LMW glutenins and gliadins allows breeders to combine protein content and quality more effectively. The use of molecular-marker-assisted selection and genetic transformation is expected to accelerate the tailoring of new wheat varieties to meet specific end-use quality requirements. Accumulating desirable quality genes will help reduce genotype X environment effects on quality-presently among the major challenges confronting breeders.     

Effects of free air carbon dioxide enrichment and nitrogen supply on growth and yield of winter barley cultivated in a crop rotation

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate growth of C₃ crops. Although barley is one of the important cereals of the world, little information exists about the effect of elevated [CO₂] on grain yield of this crop, and realistic data from field experiments are lacking. Therefore, winter barley was grown within a crop rotation over two rotation cycles (2000 and 2003) at present and elevated [CO₂](375 ppm and 550 ppm) and at two levels of nitrogen supply (adequate (N2): 262 kg ha⁻¹ in 1st year and 179 kg ha⁻¹ in 2nd year) and 50% of adequate (N1)). The experiments were carried out in a free air CO₂ enrichment (FACE) system in Braunschweig, Germany. The reduction in nitrogen supply decreased seasonal radiation absorption of the green canopy under ambient [CO₂] by 23%, while CO₂ enrichment had a positive effect under low nitrogen (+8%). Radiation use efficiency was increased by CO₂ elevation under both N levels (+12%). The CO₂ effect on final above ground biomass was similar for both nitrogen treatments (N1: +16%; N2: +13%). CO₂ enrichment did not affect leaf biomass, but increased ear and stem biomass. In addition, final stem dry weight was higher under low (+27%) than under high nitrogen (+13%). Similar findings were obtained for the amount of stem reserves available during grain filling. Relative CO₂ response of grain yield was independent of nitrogen supply (N1: +13%; N2: +12%). The positive CO₂ effect on grain yield was primarily due to a higher grain number, while changes of individual grain weight were small. This corresponds to the findings that under low nitrogen grain growth was unaffected by CO₂ and that under adequate nitrogen the positive effect on grain filling rate was counterbalanced by shortening of grain filling duration.     

Breeding for increased grain protein and micronutrient content in wheat: Ten years of the GPC-B1 gene

To provide food and nutrition security for a growing world population, continued improvements in the yield and nutritional quality of agricultural crops will be required. Wheat is an important source of calories, protein and micronutrients and is thus a priority to breed for improvements in these traits. The GRAIN PROTEIN CONTENT-B1 (GPC-B1) gene is a positive regulator of nutrient translocation which increases protein, iron and zinc concentration in the wheat grain. In the ten years since it was cloned, the impacts of GPC-B1 allelic variation on quality and yield traits have been extensively analyzed in diverse genetic backgrounds in field studies spanning forty environments and seven countries. In this review, we compile data from twenty-five studies to summarize the impact of GPC-B1 allelic variation on fifty different traits. Taken together, the results demonstrate that the functional copy of the GPC-B1 gene is associated with consistent positive effects on grain protein, Fe and Zn content with only marginally negative impacts on yield. We conclude that the GPC-B1 gene has the potential to increase nutritional and end use quality in a wide range of modern cultivars and environments and discuss the possibilities for its application in wheat breeding.     

Implications of Elevated CO2-Induced Changes in Agroecosystem Productivity

SUMMARY

Since CO₂ is a primary input for crop growth, there is interest in how increasing atmospheric CO₂ will affect crop productivity and alter cropping system management. Effects of elevated CO₂ on grain and residue production will be influenced by crop selection. This field study evaluated soybean [C₃; Glycine max(L.) Merr.] and grain sorghum [C₄; Sorghum bicolor (L.) Moench.] cropping systems managed under conservation tillage practices and two atmospheric CO₂ concentrations (ambient and twice ambient) for three growing seasons. Elevated CO₂ increased soybean and sorghum yield by 53% and 17% increase, respectively; reductions in whole plant water use were also greater for soybean than sorghum. These findings suggest that increasing CO₂ could improve future food security, especially in soybean production systems. Elevated CO₂ increased aboveground residue production by > 35% for both crops; such shifts could complement conservation management by increasing soil surface cover, thereby reducing soil erosion. However, increased residue could negatively impact crop stand establishment and implement effectiveness during tillage operations. Elevated CO₂ increased total belowground dry weight for both crops; increased root proliferation may alter soil structural characteristics (e.g., due to increased number and extent of root channels) which could lead to increases in porosity, infiltration rates, and subsequent soil water storage. Nitrate leaching was reduced during the growing season (due to increased N capture by high CO₂-grown crops), and also during the fallow period (likely a result of altered decomposition patterns due to increased C:N ratios of the high CO₂-grown material). Enhanced crop growth (both above-and be-lowground) under elevated CO₂ suggests greater delivery of C to soil, more soil surface residue, and greater percent ground coverage which could reduce soil C losses, increase soil C storage, and help ameliorate the rise in atmospheric CO₂. Results from this study suggests that the biodegradability of crop residues and soil C storage may not only be affected by the environment they were produced in but may also be species dependent. To more fully elucidate the relationships between crop productivity, nutrient cycling, and decomposition of plant materials produced in elevated CO₂ environments, future studies must address species effects (including use of genetically modified crops) and must also consider other factors such as cover crops, crop rotations, soil series, tillage practices, weed management, and regional climatic differences.     

Elevated atmospheric CO2 effects on N fertilization in grain sorghum and soybean

Increasing atmospheric CO₂ concentration has led to concerns about global changes to the environment. One area of global change that has not been fully addressed is the effect of elevated atmospheric CO₂ on agriculture production inputs. Elevated CO₂ concentration alterations of plant growth and C:N ratios may modify C and N cycling in soil and N fertility. This study was conducted to examine the effects of legume, soybean (Glycine max (L.) Merr.), and non-legume, grain sorghum (Sorghum bicolor (L.) Moench.) carbon dioxide-enriched agro-ecosystems on N soil fertility in a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split-plot design replicated three times with crop species (soybean and grain sorghum) as the main plots and CO₂ concentration (ambient and twice ambient) as subplots using open top field chambers. Fertilizer application was made with ${}^{15}\text{N}$-depleted NH₄NO₃ to act as a fertilizer tracer. Elevated CO₂ increased total biomass production in all 3 years of both grain sorghum (average 30%) and soybean (average 40%). With soybean, while no impact on the plant C:N ratio was observed, the total N content was greatly increased (average 29%) due to increased atmospheric N₂ fixation with elevated CO₂ concentration. With grain sorghum, the total N uptake was not affected, but the C:N ratio was markedly increased (average 31%) by elevated CO₂. No impact of elevated CO₂ level was observed for fertilizer N in grain sorghum. The results from this study indicated that while elevated CO₂ may enhance crop production and change N status in plant tissue, changes to soil N fertilizer application practices may not be needed.     

Heat-tolerant rice cultivars retain grain appearance quality under free-air CO2 enrichment

Background

Heat-tolerant rice cultivars have been developed as a countermeasure to poor grain appearance quality under high temperatures. Recent studies showed that elevated CO₂ concentrations (E-[CO₂]) also reduce grain quality. To determine whether heat-tolerant cultivars also tolerate E-[CO₂], we conducted a free-air CO₂ enrichment (FACE) experiment with 12 rice cultivars differing in heat tolerance.

Results

The percentage of undamaged grains of five standard cultivars (Akitakomachi, Kinuhikari, Koshihikari, Matsuribare, Nipponbare) averaged 61.7% in the ambient [CO₂] (AMB) plot and 51.7% in the FACE plot, whereas that of heat-tolerant cultivars (Eminokizuna, Wa2398, Kanto 257, Toyama 80, Mineharuka, Kanto 259, Saikai 290) averaged 73.5% in AMB and 71.3% in FACE. This resulted in a significant [CO₂] by cultivar interaction. The percentage of white-base or white-back grains increased from 8.4% in AMB to 17.1% in FACE in the sensitive cultivars, but from only 2.1% in AMB to only 4.4% in FACE in the heat-tolerant cultivars.

Conclusion

Heat-tolerant cultivars retained their grain appearance quality at E-[CO₂] under present air temperatures. Further improvements in appearance quality under present conditions will be needed to achieve improvements under E-[CO₂], because E-[CO₂] will likely lower the threshold temperature for heat stress.     

Increasing atmospheric CO2 modifies durum wheat grain quality and pasta cooking quality

The present study focused on the quality traits of durum wheat grains (protein and content, gluten content, yellow pigment content), semolina (gluten index and yellow index) and pasta (firmness, yellow index, cooking time) obtained from 12 durum wheat genotypes grown under elevated atmospheric CO₂ concentration in an open field Free Air CO₂ Enrichment (FACE) experiment. The aims were to evaluate the impact of elevated CO₂ on durum wheat pasta making related traits as well as investigate genetic differences existing in a panel of old and modern cultivars. The protein content showed a not significant decrease (7%), the GC decreased significantly (13.3%), while the GI showed an increasing significant tendency (14%). The overall pasta quality (firmness and weight) worsened in ELE. Correlation between all traits and pasta firmness demonstrated that the decrease in pasta firmness under ELE was correlated with GPC and GC while it was not with the GI. All varieties, although to different extent, showed lower pasta firmness values compared to the ambient condition. Among the varieties tested, some were more sensitive than others to the increased atmospheric CO₂ concentration, a finding that can be exploited by breeding for designing novel genotypes with lower sensitivity to increased atmospheric CO₂.     

Changes of soluble protein expression and leaf metabolite levels in Arabidopsis thaliana grown in elevated atmospheric carbon dioxide

Plant responses to elevated atmospheric CO₂ vary with species and with environmental conditions. Rates of dry matter formation were initially enhanced in response to CO₂ enrichment but these accelerated growth rates typically were not maintained over long periods of time. The objective of this study was to better understand the basis for this acclimation process. Changes of metabolite levels and of total protein expression in response to CO₂ enrichment were studied using biochemical assays and two-dimensional gel electrophoresis. Arabidopsis thaliana (L.) Henyh. (Columbia ecotype) plants were grown for 2–6 weeks in controlled environment chambers providing 36 (ambient) or 100 (elevated) Pa CO₂. Averaged over all harvest dates above-ground biomass was greater (P < 0.05) in the elevated than in the ambient CO₂ treatment but shoot biomass did not differ between treatments on the final harvest. Flowering was delayed by CO₂ enrichment. One or more flowers were observed for 52% and 100% of the elevated and ambient CO₂ grown plants, respectively, after 4-weeks growth. Starch and sucrose levels were increased 132 and 43%, respectively, in leaves of 6-week-old plants in response to CO₂ enrichment. Nitrate varied with plant age, although mean nitrate levels in rosettes were decreased 31% by CO₂ enrichment when averaged over all harvest dates. Chlorophyll, the chlorophyll a/b ratio, carotenoids and total soluble protein did not differ between CO₂ treatments. Total Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity decreased with plant age and was lower (P < 0.01) in the elevated compared to the ambient CO₂ treatment. The above results suggested that acclimation to elevated CO₂ occurred in Arabidopsis without developing symptoms of N-deficiency. A total of 400 major proteins were separated and compared by two-dimensional gel electrophoresis. No proteins appeared de novo or disappeared in response to CO₂ enrichment, although pixel densities for 13 protein spots differed significantly between CO₂ treatments on at least one harvest date. Six of these proteins were identified by mass spectrometry. Three of these identified proteins were involved in plant growth and development or were associated with stress. Two other proteins were encoded by genes with putative functions. Only one protein, the 23 kDa subunit of the oxygen evolving complex (OEC23), was involved in photosynthesis. It was concluded that long-term plant growth in elevated CO₂ caused only small changes in the Arabidopsis proteome.     

CO2 fertilization does not affect biomass production and nutritive value of a C4 tropical grass in short timeframe

Increased atmospheric carbon dioxide (CO₂) is a consequence of recent anthropogenic environmental changes, and few studies have evaluated its effects on tropical grasses used in Brazilian pastures, the main feed source for major part of ruminant livestock. This study evaluated forage production, chemical composition, in vitro total gas production and organic matter degradability of Brachiaria brizantha under contrasting CO₂ atmospheric conditions in a free air carbon dioxide enrichment (FACE) facility. The forage plants were sown in each of the 12 octagonal rings of the FACE facility: six under ambient atmospheric CO₂ concentration of approximately 390 μmol/mol, hereafter referred to as control (CON) plots, and other six rings enriched with pure CO₂ flux to achieve a target CO₂ concentration of 550 μmol/mol, hereafter called elevated CO₂ (eCO₂) plots. Soil samples were collected to determine carbon and nitrogen concentrations. After seventy days of sowing, a standardization cutting was performed and then at regular intervals of 21 days the forage was harvested (ten harvest dates) and forwarded to laboratorial analyses. Forage above‐ground biomass production (dry matter (DM): 6,143 vs. 6,554 kg/ha), as well as morphological characteristics (leaves: 71% vs. 68%; stem: 28% vs. 31%), chemical composition (crude protein: 162.9 vs. 161.8; neutral detergent fibre: 663.8 vs. 664.3; acid detergent fibre: 369.5 vs. 381; lignin: 60.1 vs. 64.1 g/kg DM; total C: 45.9 vs. 45.9; total N: 2.8 vs. 2.8; total S: 0.2% vs. 0.2%), organic matter in vitro degradability (573.5 vs. 585.3 g/kg), methane (5.7 vs. 4.3 ml/g DM) and total gas (128.3 vs. 94.5 ml/g DM) production did not differ significantly between CON and eCO₂ treatments (p > .05). The results indicated that at least under short‐term enrichment, B. brizantha was not affected by eCO₂.