Elevated Atmospheric CO2 Concentration Has Limited Effect on Wheat Grain Quality Regardless of Nitrogen Supply.

Elevated atmospheric CO2 concentrations (e[CO2]) can decrease the grain quality of wheat. However, little information exists concerning interactions between e[CO2] and nitrogen fertilization on important grain quality traits. To investigate this, a 2-year free air CO2 enrichment (FACE) experiment was conducted with two CO2 (393 and 600 ppm) and three (deficiency, adequate, and excess) nitrogen levels. Concentrations of flour proteins (albumins/globulins, gliadins, and glutenins) and key minerals (iron, zinc, and sulfur) and baking quality (loaf volume) were markedly increased by increasing nitrogen levels and varied between years. e[CO2] resulted in slightly decreased albumin/globulin and total gluten concentration under all nitrogen conditions, whereas loaf volume and mineral concentrations remained unaffected. Two-dimensional gel electrophoresis revealed strong effects of nitrogen supply and year on the grain proteome. Under adequate nitrogen, the grain proteome was affected by e[CO2] with 19 downregulated and 17 upregulated protein spots. The downregulated proteins comprised globulins but no gluten proteins. e[CO2] resulted in decreased crude protein concentration at maximum loaf volume. The present study contrasts with other FACE studies showing markedly stronger negative impacts of e[CO2] on chemical grain quality, and the reasons for that might be differences between genotypes, soil conditions, or the extent of growth stimulation by e[CO2].

Narrowing uncertainties in the effects of elevated CO2 on crops.

Plant responses to rising atmospheric carbon dioxide (CO2) concentrations, together with projected variations in temperature and precipitation will determine future agricultural production. Estimates of the impacts of climate change on agriculture provide essential information to design effective adaptation strategies, and develop sustainable food systems. Here, we review the current experimental evidence and crop models on the effects of elevated CO2 concentrations. Recent concerted efforts have narrowed the uncertainties in CO2-induced crop responses so that climate change impact simulations omitting CO2 can now be eliminated. To address remaining knowledge gaps and uncertainties in estimating the effects of elevated CO2 and climate change on crops, future research should expand experiments on more crop species under a wider range of growing conditions, improve the representation of responses to climate extremes in crop models, and simulate additional crop physiological processes related to nutritional quality.

Response of maize biomass and soil water fluxes on elevated CO2 and drought-From field experiments to process-based simulations.

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

Effects of free air carbon dioxide enrichment (FACE) on nitrogen assimilation and growth of winter wheat under nitrate and ammonium fertilization.

A 2-year Free Air CO2 Enrichment (FACE) experiment was conducted with winter wheat. It was investigated whether elevated atmospheric CO2 concentration (e[CO2 ]) inhibit nitrate assimilation and whether better growth and nitrogen acquisition under e[CO2 ] can be achieved with an ammonium-based fertilization as it was observed in hydroponic culture with wheat. Under e[CO2 ] a decrease in nitrate assimilation has been discussed as the cause for observed declines in protein concentration in C3 cereals. Wheat was grown under ambient [CO2 ] and e[CO2 ] (600 ppm) with three levels (deficiency, optimal, and excessive) of nitrate-based fertilization (calcium ammonium nitrate; CAN) or with optimal ammonium-based fertilization. Ammonium fertilization was applied via injection of an ammonium solution into the soil in the 1st year and by surface application of urea combined with nitrification inhibitors (UNI) in the 2nd year. Results showed that ammonium-based fertilization was successfully achieved in the 2nd year with respect to nitrification control, as soil ammonium concentration was considerably higher over the growing season for UNI fertilized plots compared to optimal CAN plots. Also, stem nitrate concentration, flag leaf nitrate reductase activity, and transcript levels were lower in UNI fertilized plants compared to optimal CAN. Regarding the e[CO2 ] effect on nitrate reductase activity and transcript levels, no alteration could be observed for any nitrogen fertilizer treatment. Flag leaf growth was stimulated under e[CO2 ] leading to an enhanced nitrate reductase activity referred to m2 ground area at late flowering being in line with a higher nitrogen acquisition under e[CO2 ]. Moreover, nitrogen acquisition was considerably higher in nitrate fertilized plants compared to ammonium fertilized plants under e[CO2 ]. Our results obtained under field conditions show that a change from nitrate- to ammonium-based fertilization will not lead to a better growth and nitrogen acquisition of winter wheat under future e[CO2 ].

Effect of rising atmospheric carbon dioxide concentration on the protein composition of cereal grain.

The present study investigates effects of rising atmospheric CO2 concentration on protein composition of maize, wheat, and barley grain, especially on the fractions prolamins and glutelins. Cereals were grown at different atmospheric CO2 concentrations to simulate future climate conditions. Influences of two nitrogen fertilization levels were studied for wheat and barley. Enriched CO2 caused an increase of globulin and B-hordein of barley. In maize, the content of globulin, α-zein, and LMW polymers decreased, whereas total glutelin, zein, δ-zein, and HMW polymers rose. Different N supplies resulted in variations of barley subfractions and wheat globulin. Other environmental influences showed effects on the content of nearly all fractions and subfractions. Variations in starch-protein bodies caused by different CO2 treatments could be visualized by scanning electron microscopy. In conclusion, climate change would have impacts on structural composition of proteins and, consequently, on the nutritional value of cereals.

The effect of free air carbon dioxide enrichment and nitrogen fertilisation on the chemical composition and nutritional value of wheat and barley grain.

A rising atmospheric CO2 concentration might influence the nutrient composition of feedstuffs and consequently the nutritional value for livestock. The present study investigates the effects of atmospheric CO2 enrichment on the chemical composition and nutritional value of winter wheat cv. "Batis" and winter barley cv. "Theresa". Both cereals were grown at two different atmospheric CO2 concentrations (ambient CO2 [AMBI]: 380 ppm and enriched CO2 [free air carbon dioxide enrichment, FACE]: 550 ppm) for two growing seasons. The influence of two different nitrogen (N) fertilisation levels (adequate N supply [N100] and nearly 50% of adequate N supply [N50]) were studied as well. A significant effect was observed for the crude protein content, which declined at FACE condition in a range of 8-16 g kg(-1) in wheat and of 10-20 g kg(-1) in barley. A reduced N fertilisation level resulted in a strong reduction of crude protein concentration in both cereal species. In wheat, a decrease in N supply significantly enhanced the concentration of starch and crude fibre. In barley, only the concentration of fructose increased under FACE condition and reduced N fertilisation. The FACE did not have major effects on the concentrations of minerals, while the influence of N fertilisation was different for both cereals. Whereas no effects could be observed for barley, a reduced N supply caused a significant reduction in concentrations of zinc, manganese and iron in wheat. Furthermore, an undirected effect of atmospheric CO2 and N fertilisation levels were found for the amino acid concentrations. Based on these results, future scenarios of climate change would have an impact on the nutritional value of cereal grains.

Elevated CO(2) and drought stress effects on the chemical composition of maize plants, their ruminal fermentation and microbial diversity in vitro.

Climate changes are supposed to influence productivity and chemical composition of plants. In the present experiments, it was hypothesised that the incubation of plants exposed to elevated atmospheric carbon dioxide concentrations ([CO2]) and drought stress will result in different ruminal fermentation pattern and microbial diversity compared to unaffected plants. Maize plants were grown, well-watered under ambient (380 ppm CO2, Variant A) and elevated [CO2] (550 ppm CO2, Variant B). Furthermore, each CO2 treatment was also exposed to drought stress (380 ppm and 550 ppm CO2,Variants C and D, respectively), which received only half as much water as the well-watered plants. Plant material from these treatments was incubated in a semi-continuous in vitro fermentation experiment using the rumen simulation technique. Single strand conformation polymorphism (SSCP) analysis was conducted for Bacteria and Archaea specific profiles. The analysis of crude nutrients showed higher contents of fibre fraction in drought stress Variants C and D. Crude protein content was increased by drought stress under ambient but not under elevated [CO2]. Fermentation of drought stress variants resulted in significantly increased pH values, decreased digestibilities of organic matter and increased ammonia-N (NH3-N) concentrations compared with well-watered variants. Additionally, the 550 ppm CO2 Variants B and D showed significantly lower NH3-N concentrations than Variants A and C. The Bacteria- and Archaea-specific SSCP profiles as well as the production rates of short-chain fatty acids and their molar percentages were not affected by treatments. During the first four days of equilibration period, a decrease of molar percentage of acetate and increased molar percentages of propionate were observed for all treatments. These alterations might have been induced by adaptation of the in vitro system to the new substrate. The rumen microflora appeared to be highly adaptive and could cope with altered contents of crude nutrients in plants as induced by elevated [CO2] and drought stress.

Effects of free air carbon dioxide enrichment and drought stress on the feed value of maize silage fed to sheep at different thermal regimes.

Information about the effects of rising atmospheric CO2 concentration and drought on the feed value of maize silage and interactions with the thermal environment during feeding is limited. A free air carbon dioxide enrichment facility was operated in a maize field to generate an elevated CO2 concentration of 550 ppm. Drought was induced by the exclusion of precipitation in one half of all experimental plots. Plants were harvested, chopped and ensiled. In a balance experiment on sheep, the nutrient digestibility was determined for three climatic treatments (temperate, temperature humidity index (THI) 57-63; mild heat, THI 68-71; severe heat, THI 75-80). The CO2 concentration and drought did not alter the crude nutrient content of silage dry matter (DM) or nutrient and organic matter (OM) digestibility. Drought increased the concentration of deoxynivalenol (DON, p < 0.001). The drought-associated increase of DON was reduced by CO2 enrichment (p = 0.003). The lowest digestibility of acid detergent fibre (p = 0.024) and neutral detergent fibre (p = 0.005) was observed during the coldest climate. OM digestibility increased during mild heat (p = 0.023). This study did not indicate considerable alterations of the feed value of maize silage due to increased atmospheric CO2 and drought. Enriched CO2 may decrease DON contaminations during drought. The thermal environment during the balance experiment did not interact with feeding maize silage grown under elevated CO2, but may affect cell wall and OM digestibility.

Effects of the thermal environment on metabolism of deoxynivalenol and thermoregulatory response of sheep fed on corn silage grown at enriched atmospheric carbon dioxide and drought.

Future livestock production is likely to be affected by both rising ambient temperatures and indirect effects mediated by modified growth conditions of feed plants such as increased atmospheric CO2 concentrations and drought. Corn was grown at elevated CO2 concentrations of 550 ppm and drought stress using free air carbon dioxide enrichment technology. Whole plant silages were generated and fed to sheep kept at three climatic treatments. Differential blood count was performed. Plasma DON and de-epoxy-DON concentration were measured. Warmer environment increased rectal and skin temperatures and respiration rates (p < 0.001 each) but did not affect blood parameters and the almost complete metabolization of DON into de-epoxy-DON. Altered growth conditions of the corn fed did not have single effects on sheep body temperature measures and differential blood count. Though the thermoregulatory activity of sheep was influenced by the thermal environment, the investigated cultivation factors did not indicate considerable impacts on the analysed parameters.

Effects of elevated atmospheric CO2 concentrations on the quantitative protein composition of wheat grain.

The continuing increase in atmospheric CO 2 concentration is predicted to enhance biomass production and to alter biochemical composition of plant tissues. In the present study, winter wheat ( Triticum aestivum L. cv. 'Batis') was grown under ambient air (BLOW, CO 2 concentration: 385 muL L (-1)) and free-air CO 2 enrichment (FACE, CO 2 concentration: 550 muL l (-1)) and two different nitrogen (N) fertilization levels (normal N supply: N100, 50% of normal N supply: N50). Mature kernels were milled into white flour and analyzed for the contents of crude protein, Osborne fractions, single gluten protein types and glutenin macropolymer. Elevated CO 2 caused significant reductions in crude protein and all protein fractions and types ( p < 0.001) except albumins and globulins. Effects were more pronounced in wheat samples supplied with normal amounts of N fertilizer. Crude protein was reduced by 14% (N100) and 9% (N50), gliadins by 20% and 13%, glutenins by 15% and 15% and glutenin macropolymer by 19% and 16%, respectively. Within gliadins, omega5-gliadins (-35/-22%) and omega1,2-gliadins (-27/-14%) were more affected than alpha-gliadins (-21/-13%) and gamma-gliadins (-16/-12%). Within glutenins, HMW subunits (-23/-18%) were more affected than LMW subunits (-12/-15%). According to these results, flour from high CO 2 grown grain will have a diminished baking quality. To our knowledge, these are the first results of elevated CO 2 concentrations impacts on wheat grain protein composition gained under relevant growing conditions at least for Central Europe.

Next generation of elevated [CO2] experiments with crops: a critical investment for feeding the future world.

A rising global population and demand for protein-rich diets are increasing pressure to maximize agricultural productivity. Rising atmospheric [CO(2)] is altering global temperature and precipitation patterns, which challenges agricultural productivity. While rising [CO(2)] provides a unique opportunity to increase the productivity of C(3) crops, average yield stimulation observed to date is well below potential gains. Thus, there is room for improving productivity. However, only a fraction of available germplasm of crops has been tested for CO(2) responsiveness. Yield is a complex phenotypic trait determined by the interactions of a genotype with the environment. Selection of promising genotypes and characterization of response mechanisms will only be effective if crop improvement and systems biology approaches are closely linked to production environments, that is, on the farm within major growing regions. Free air CO(2) enrichment (FACE) experiments can provide the platform upon which to conduct genetic screening and elucidate the inheritance and mechanisms that underlie genotypic differences in productivity under elevated [CO(2)]. We propose a new generation of large-scale, low-cost per unit area FACE experiments to identify the most CO(2)-responsive genotypes and provide starting lines for future breeding programmes. This is necessary if we are to realize the potential for yield gains in the future.