Effect of Free Air Carbon Dioxide Enrichment (FACE) on the Chemical Composition and Nutritive Value of Wheat Grain and Straw

Authors: PORTEAUS, F - University Of Essex; HILL, J - University Of Melbourne; BALL, A - Flinders University; Pinter Jr, Paul; Kimball, Bruce; Wall, Gerard - Gary; Adamsen, Floyd; Hunsaker, Douglas - Doug; LAMORTE, ROBERT - US Department Of Agriculture (USDA); LEAVITT, S - University Of Arizona; THOMPSON, T - University Of Arizona; MATTIAS, A - University Of Arizona; BROOKS, T - University Of Arizona; Morris, Craig

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2008
Publication Date: 3/9/2009
Citation: Porteaus, F., Hill, J., Ball, A.S., Pinter Jr, P.J., Kimball, B.A., Wall, G.W., Adamsen, F.J., Hunsaker, D.J., Lamorte, R.L., Leavitt, S.W., Thompson, T.L., Mattias, A.D., Brooks, T.J., Morris, C.F. 2009. Effect of Free Air Carbon Dioxide Enrichment (FACE) on the Chemical Composition and Nutritive Value of Wheat Grain and Straw. Animal Feed Science And Technology. 149:322-332

Interpretive Summary: Atmospheric levels of CO2 concentration are increasing, but the likely consequences on wheat straw and grain nutritional quality are largely unknown. Therefore, wheat grain and straw samples from a free-air CO2 enrichment (FACE) experiment conducted at ample and limiting levels of soil nitrogen (N) fertilizer were analyzed for several chemical and nutritional analyses. Generally, applications of N fertilizer increased the N concentrations of the wheat straw and grain at ambient levels of CO2, whereas at elevated CO2, the concentrations were not increased as much. This implies that at the same levels of fertilizer application (which were considered large), that the nutritional value of the straw and grain will decrease in the future. Such information is needed to develop management strategies in the future, which will benefit all consumers of wheat and other grain food and feed products.

Technical Abstract: The global impact of increasing concentrations of CO2 in the atmosphere on plants has been studied extensively recently but little information has been published on the effect of enrichment of atmospheric CO2 on the development of nutritive value of grain and straw for ruminant feeds. This paper reports the chemical composition and nutritive value of grain and straw harvested from the drought tolerant hard red spring wheat (Triticum aestivum L.) variety Yecora Rojo managed with two carbon dioxide regimes (ambient, 350 µl/l and elevated, 550 µl/l), two rates of nitrogen application (low N: 53 kg N/ha and high N: 393 kg N/ha) under a water-fed (no deficit) regime. Accumulation of carbon in straw did not differ among crops grown at elevated CO2 and low N supplementation and crops grown under ambient CO2 with low levels of N supplementation. Increased N application increased sequestration of C (P<0.05) compared to straw from crops grown under ambient CO2 concentration. Low levels of N application and elevated CO2 led to straw containing similar concentrations of N to those grown under ambient CO2 conditions. Increasing N application to crops grown under ambient concentrations of CO2 elevated the concentration of N (P<0.01) whereas crops grown at elevated concentrations of CO2 did not accumulate N to the same extent. Differences in non structural carbohydrate and cell wall content reflected the patterns observed for total C. No effect of increasing the concentration of CO2 on WSC, aNDFom, ADFom, hemicellulose, cellulose and lignin (sa) occured. There was a small decline (-26 g/kg; P<0.05) in the concentration of aNDFom in straw from crops that had received high N input. The ratio of lignin to total N was higher in straw harvested from plots with elevated CO2 (33.5:1) compared with ambient CO2 (24.6:1). No changes in the total C content occurred for grain samples in response to CO2 concentration or supplemental N fertiliser. No interaction between supply of Nitrogen and CO2 concentration occured. Changes in the total N content of grain in response to treatments were similar to the changes observed in the straw fraction. The increases in concentration of N incorporated in the grain were higher from crops grown under enriched concentrations of CO2 (+8.6 g/kg; P<0.01) than for crops grown under ambient supply of CO2 (+3.5 g/kg; P<0.05). Differences in concentration of starch in the grain with increasing supply of N from fertiliser occurred under FACE conditions (P<0.05), but not for grain harvested from those grown under ambient CO2 levels. No effect of changing concentrations of CO2 were observed for ADFom, lignin(sa), cellulose and neutral detergent cellulose digestability but higher concentrations of aNDFom (P<0.05) and hemicellulose (P<0.05) were higher in grain grown under ambient concentrations of CO2 irrespective of supply of N to the crop. Although effects of elevated concentrations of CO2 on grain and straw quality were expected, this poses concerns for livestock production in systems that use lower levels of agronomic inputs. Elevated concentrations of CO2 in the ambient environment were beneficial for the development of above ground biomass and grain yield as measured by thousand grain weight. However straw and grain quality, in terms of crude protein and the crude protein to energy ratio will be affected by increasing concentrations of CO2 in the atmosphere, and this may lead to a reduction in the total supply of crude protein in crops used by livestock.