Effect of free-air CO2 enrichment (FACE) on forage quality of wheat

Abstract Wheat ( Triticum aestivum L., cultivar ‘Yecora rojo’) was grown in ambient (370 μmol mol −1 ) or enriched (550 μmol mol −1 ) concentrations of CO 2 in the free-air CO 2 enrichment (FACE) project, and components were analyzed for in vitro digestibility, fiber constituents, and crude protein. Four replicated plots of each CO 2 treatment were split for irrigation: ‘wet’ regions received 60 cm of water and ‘dry’ regions received 30 cm of water through underground tubes. Enriched CO 2 concentrations had no effect on in vitro digestion of intact sections of young (26–32-day-old plants) leaf blades except at 24–27 h incubation, at which time enriched leaves were lower in digestibility than control ones. Enriched CO 2 concentrations increased the content of acid detergent fiber (ADF) and cellulose of young wet leaves. Sections of main shoots at 26 days tended to have increased digestibility with elevated CO 2 levels. Enriched CO 2 concentrations did not alter the digestibility of flag leaves from 105-day-old plants or of flag leaves, uppermost stems, and sheaths from plants at full grain maturity. Enriched CO 2 levels reduced the acid detergent lignin (ADL) and tended to reduce the protein of leaves from 105-day-old plants. For mature leaf blades, neutral detergent fiber, ADF, and cellulose were, or tended to be, higher while protein content tended to be lower in elevated CO 2 -grown plants; for both CO 2 treatments, ‘dry’ leaves were higher in digestibility and lower in ADL than ‘wet’ samples. Mature stems plus sheaths had lower protein contents in plants grown in elevated CO 2 . Results indicated that enriched CO 2 concentrations to 550 μmol mol −1 did not substantially alter wheat in vitro digestibility, regardless of irrigation treatment. Elevated CO 2 altered fiber components and protein, but these were not consistent among parts and harvests.