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

Wheat (Triticum aestivum L., cultivar ‘Yecora rojo’) was grown in ambient (370 μmol mol−1) or enriched (550 μmol mol−1) concentrations of CO2 in the free-air CO2 enrichment (FACE) project, and components were analyzed for in vitro digestibility, fiber constituents, and crude protein. Four replicated plots of each CO2 treatment were split for irrigation: ‘wet’ regions received 60 cm of water and ‘dry’ regions received 30 cm of water through underground tubes. Enriched CO2 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 CO2 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 CO2 levels. Enriched CO2 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 CO2 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 CO2-grown plants; for both CO2 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 CO2. Results indicated that enriched CO2 concentrations to 550 μmol mol−1 did not substantially alter wheat in vitro digestibility, regardless of irrigation treatment. Elevated CO2 altered fiber components and protein, but these were not consistent among parts and harvests.