Biomass responses in a temperate European grassland through 17 years of elevated CO2.

Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the "GiFACE" experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2 (eCO2 ) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014, aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = .045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.

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 ].

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].

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 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 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.