Effects of elevated CO2 concentration on bulbil germination and early seedling growth in Chinese yam under different air temperatures

The present study investigated the effects of elevated carbon dioxide concentration ([CO₂]) and air temperature on the germination of seed bulbils and the seedling vigour of two Chinese yam lines. Plants were grown under two [CO₂] levels, ambient and elevated (ambient + 200 μmol mol^?1), and two mean air temperature regimes, 22.2 °C (ambient + 1.4 °C) and 25.6 °C (ambient + 5.2 °C). Elevated [CO₂] did not affect bulbil germination under both air temperature regimes. During the early growth stage, the dry weight (DW) of leaves, vines, shoots, roots, belowground parts (roots + tubers) and whole plants were higher under elevated [CO₂] than ambient [CO₂] for both lines under the low- and high-temperature regimes. The values of vigour indexes (index I = germination % × seedling length and index II = germination % × seedling DW) were also higher under elevated [CO₂] than ambient [CO₂] for both lines. These results indicated that Chinese yam seedlings respond positively to elevated [CO₂] during the early growth stage. The above:belowground DW ratios were lower under elevated [CO₂] than ambient [CO₂] in seedlings with very small new tubers for both yam lines, indicating that elevated [CO₂] strongly affected the root growth in the early growth stage. The DWs of post-treatment seed bulbils were higher in the elevated [CO₂] under both air temperature regimes. The results showed that Chinese yam used a smaller amount of the reserves in seed bulbils under elevated [CO₂] than under ambient [CO₂].     

Effects of elevated atmospheric CO2 concentration on morphology of leaf blades in Chinese yam

ABSTRACT

The effects of elevated carbon dioxide concentration on the morphology of leaf blades in two Chinese yam lines under different temperature conditions were determined. Plants were grown under two [CO₂] levels, ambient (about 400 µmol mol^?1) and elevated (ambient + 200 µmol mol^?1) in the daytime, and two mean air temperature regimes, approximately ambient temperature (22.2°C) and high temperature (25.6°C). The palisade layer was thicker under elevated [CO₂] than under ambient [CO₂] in both temperature regimes, and the whole yam leaf blade was thicker under elevated [CO₂] than under ambient [CO₂] in the approximately ambient temperature regime. The numbers of chloroplasts per palisade cell and spongy cell as well as per unit profile area of palisade cell, number of starch grains per chloroplast, profile area of the starch grain, and starch-to-chloroplast area ratio in both palisade and spongy cells were higher under elevated [CO₂] than under ambient [CO₂] in both temperature regimes. Furthermore, the stomatal density on the abaxial side of the leaf blade in Chinese yam was greater under elevated [CO₂] than under ambient [CO₂] under both temperature regimes, and stomatal-pore length was higher under elevated [CO₂] than under ambient [CO₂] in the approximately ambient temperature regime. These results indicate that elevated [CO₂] positively affects the photosynthetic apparatus. The results of this study provide information for understanding the response characteristics of the leaf blade under elevated [CO₂] and a possible explanation for the positive photosynthetic responses of Chinese yam to elevated [CO₂] in our previous study.

List of Abbreviations:[CO₂]: carbon dioxide concentration     

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.     

Effects of atmospheric CO2 concentration and defoliation on the growth of Themeda triandra

The effects of elevated atmospheric carbon dioxide (CO₂) concentration (700 μmol mol^?1) on defoliated (three clippings at 3‐week intervals) and undefoliated plants were determined for the C₄ grass Themeda triandra, Forsk. The elevated CO₂ concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO₂ concentration treatment. The primary effect of the elevated CO₂ concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down‐regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO₂ concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO₂ concentration treatment were lost following a final 3‐week reversion to ambient CO₂ concentration, but occurred in plants exposed to the elevated CO₂ concentration for the final 3‐week period only. In conclusion, elevated atmospheric CO₂ concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO₂ responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation.     

Interactive Effects of CO2 and O3 on the Growth of Trisetum flavescens and Trifolium pratense Grown in Monoculture or a Bi-Species Mixture

SUMMARY

Golden oat grass (Trisetum flavescens L.) and red clover (Trifolium pratense L.) were grown as monocultures or bi-species mixtures under controlled conditions and exposed to ambient (350 ppm) or elevated (580 ppm) CO₂, with or without addition of O₃ (diel profile with 150 ppb maximum). Shoot biomass measurements after the initial growth and two re-growth periods were used to determine the specific responses of both species, and the difference in the specific response between monocultures and mixtures. T. pratense was much more responsive to CO₂, O₃, and their combination, compared to T. flavescens. In the case of O₃ but not of CO₂, the difference in sensitivity between species was larger in mixture than in monoculture. In contrast to elevated CO₂, O₃ significantly reduced the root:shoot ratio in the mixture, which could explain the increasing negative effect of O₃ on clover with progressing harvests.

The relative CO₂ stimulation of T. pratense and of the cumulative mixture shoot biomass was larger in the presence than in the absence of O₃, which was due to an almost complete protection from O₃ stress by elevated CO₂. In the mixture, the fraction of T. flavescens was small and increased during the experiment; this increase was most pronounced with O3, but any change in mixture biomass was dominated by the response of T. repens.

The results confirm that in grass/legume mixtures legumes are most sensitive to elevated CO₂ and O₃, but the magnitude of specific responses depends on canopy structure and of plant development. Elevated CO₂ minimizes the negative impacts of O₃ stress on above- and below-ground plant growth.     

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.     

Metabolite profiling of sheath blight disease resistance in rice: in the case of positive ion mode analysis by CE/TOF-MS

Rice sheath blight is an important disease caused by Rhizoctonia solani. The resistant and susceptible rice lines (32R and 29S, respectively) showed different responses to R. solani infection in metabolite levels. The aim of this study was to characterize the metabolite levels in rice lines during R. solani infection using capillary electrophoresis equipped with time of flight mass spectrophotometry (CE/TOF-MS) in positive ion mode. Hundred metabolites were identified and classified into six clusters by hierarchical cluster using Mass Profiler Professional software. Changes in metabolite level at inoculated 32R and 29S were mapped on branches of tricarboxylic acid and glycolysis pathway. Volcano plot successfully filtered the metabolites based on fold change and p-value. The volcano plot result showed that 10 metabolites were up and down regulated in inoculated 32R relative to 29S. One metabolite, chlorogenic acid, showed a positive response in 32R. Meanwhile, pipecolic acid showed as the highest magnitude of fold change and p-value significance level in 29S. In addition, eight amino acids; glutamate, γ-aminobutyric acid, glycine, histidine, phenylalanine, serine, tryptophan, and tyrosine showed increase in 29S after R. solani inoculation.     

Production Ecophysiology of Hungarian Green Pepper Under Elevated Air CO2 Concentration

SUMMARY

Production, dry matter (including reproductive) allocation, photosynthesis, transpiration, water use efficiency and carbon and nitrogen responses of a Hungarian sweet pepper (Capsicum annum L.) under continuous elevated CO₂ concentrations are reported. Plants were grown in open top chambers under a temperate-continental climate in Hungary from plantation at ambient (350 μmol mol^?1) and elevated (700 μmol mol^?1) CO₂ concentrations. The CO₂ assimilation responses of the green pepper plants grown in high CO₂ from plantation until final harvest reflected down-regulation of their photosynthesis. The integrated and combined effect of the increased net CO₂ assimilation rate and the unchanged rate of transpiration resulted in higher WUE at elevated CO₂ concentrations in the high CO₂ plants than in the control ones grown at ambientCO₂. However, the improved water use efficiency in the high CO₂ plants was not followed by an acclimation in C-trans-location and C-allocation to the reproductive organs in the required degree. This was reflected in a slightly increased overall plant production and higher reproductive allocation, but was not accompanied by an increased fresh or dry berry mass production. The acclimation discussed may be of advantage for plant growth in a high CO₂ environment with restricted water availability. We did not find worthy statistical difference between the yield mass of the control and elevated CO₂, although the dry matter production parameters of the high CO₂ plants had statistically not significantly higher values.     

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.     

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.     

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.     

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.     

Elevated carbon dioxide and temperature effects on rice yield,leaf greenness,and phenological stages duration

The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO₂]) (550 μmol mol^?1) and air temperature (+2–3 °C) on japonica rice (Oryza sativa L. “Ariete”) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO₂]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO₂] (average 382 μmol mol^?1). Results obtained showed that the rice “Ariete” had a moderate high yielding under open-field condition, but was susceptible to air temperature rise of +2–3 °C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO₂] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.     

Effect of CO2 Concentration,Temperature and N Fertilization on Biomass Production of Soybean Genotypes Differing in N Fixation Capacity

Abstract

We tested the hypothesis that elevated CO₂ concentration [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype that has a higher nitrogen (N) fixation capacity. Furthermore, we analyzed theinteractive effects of N fertilization, temperature and [CO₂] on biomass production. Three genetically related genotypes: Enrei (normally-nodulating genotype), Kanto 100 (supernodulating genotype), and En1282 (non-nodulating genotype) were grown in pots, with or without N fertilizer for two years (2004, 2005). They were then subjected to two different [CO₂] (ambient and elevated (ambient + 200 ?mol mol-¹)) × two temperature regimes (low,high (low + 4~5ºC)). Top dry weight at maturity was the greatest in the elevated [CO₂] × high temperature regime, irrespective of genotype and N fertilization. The [CO₂] elevation generally enhanced N acquisition and dry matter production during the vegetative growth stage, and the enhancement was more pronounced in the nodulating genotypes (Enrei and Kanto 100) than in the non-nodulating genotype (En1282), indicating that N supply through N fixation contributes to elevated [CO₂]-induced biomass production in soybean. However, the relative responsiveness ofbiomass production to elevated [CO₂] was not necessarily higher in the supernodulating genotype than the normally-nodulating genotype. The N utilization efficiency to produce biomass was inferior in the supernodulating genotype than in the normally-nodulating and non-nodulating genotypes. These results did not fully verify the hypothesis that elevated [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype with a higher N fixation capacity.     

Analysis of QTLs for Flag Leaf Shape and Its Response to Elevated CO2 in Rice （Oryza sativa）

To understand the responses of flag leaf shape in rice to elevated CO2 environment and their genetic characteristics,quantitative trait loci(QTLs)for flag leaf shape in rice were mapped onto the molecular marker linkage map of chromosome segment substitution lines(CSSLs)derived from a cross between a japonica variety Asominori and an indica variety IR24 under free air carbon dioxide enrichment(FACE,200μmol/mol above current levels)and current CO2 concentration(Ambient,about 370μmol/mol).Three flag-leaf traits,flag-leaf length(LL),width(LW)and the ratio of LL to LW (RLW),were estimated for each CSSL and their parental varieties.The differences in LL,LW and RLW between parents and in LL and LW within IR24 between FACE and Ambient were significant at 1%level.The continuous distributions and transgressive segregations of LL,LW and RLW were also observed in CSSL population,showing that the three traits were quantitatively inherited under both FACE and Ambient.A total of 16 QTLs for the three traits were detected on chromosomes 1,2,3,4,6,8 and 11 with LOD(Log10-likelihood ratio)scores ranging from 3.0 to 6.7.Among them,four QTLs (qLL-6*,qLL-8*,qLW-4*,and qRLW-6*)were commonly detected under both FACE and Ambient.Therefore,based on the different responses to elevated CO2 in comparison with current CO2 level,it can be suggested that the expressions of several QTLs associated with flag-leaf shape in rice could be induced by the high CO2 level.     

Effects of Elevated Atmospheric Carbon Dioxide Concentration on Silica Deposition in Rice (Oryza sativa L.) Panicle

Abstract

The effects of elevated carbon dioxide concentration ([CO₂]) on silica deposition on husk epidermis of rice (Oryza sativa L. cv. Akitakomachi) during the flowering stage were investigated in this study. The study was motivated by the concept that the rice yield maybe affected by global warming as a result of elevated [CO₂] environment since sterility of rice is related to the panicle silica content that influences transpiration, and elevated [CO₂] could affect plant transpiration. Silica deposition analysis was focused on the flowering stage of the rice crop grown hydroponically under two [CO₂] conditions: 350 μmol mol-¹ (ambient) and 700 μmol mol-¹ (elevated). Silica deposition on the husk epidermis from three parts of the panicle at four flowering stages were examined using a scanning electron microscope (SEM) combined with an energy dispersive X-ray microanalyzer (EDX). The results demonstrated that elevated [CO₂] significantly suppressed silica deposition on the husk epidermis at the lower part of the panicle, and at the early flowering stage when 1/3 of the panicle emerged from the leaf sheath. In the transverse section analysis of the husk, silica deposition on the husk epidermis under elevated [CO₂] was less than that under ambient [CO₂] at the late flowering stage. The less silica deposition observed on the husks at the late flowering stage under elevated [CO₂] might be related to the suppressed transpiration from the panicle by elevated [CO₂] found in a previous study.     

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.     

Yield formation of CO2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice (Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO₂] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO₂ enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol⁻¹) [CO₂] under two levels of supplemental N (12.5 g Nm⁻² and 25 g Nm⁻²). Elevated [CO₂] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO₂] was independent of N fertilization, but varied among different years. On average, elevated [CO₂] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO₂], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO₂], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO₂] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO₂] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO₂] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO₂] levels.     

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.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on dry matter production and distribution of rice (Oryza sativa L.)

It is reported that stimulating effect of elevated atmospheric [CO₂] on photosynthesis of rice (Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO₂]. A free-air CO₂ enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] and supplied with 25 g N m², which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO₂] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique).