EFFECT OF FREE-AIR CO2 ENRICHMENT (FACE) ON FORAGE QUALITY OF WHEAT

Wheat (Triticum aestivum L., cultivar 'Yecora rojo') was grown in ambi ent (370 mu mol mol(-1)) or enriched (550 mu mol mol(-1)) concentratio ns of CO2 in the free-air CO2 enrichment (FACE) project, and component s were analyzed for in vitro digestibility, fiber constituents, and cr ude protein. Four replicated plots of each CO2 treatment were split fo r irrigation: 'wet' regions received 60 cm of water and 'dry' regions received 30 cm of water through underground tubes. Enriched CO2 concen trations had no effect on in vitro digestion of intact sections of you ng (26-32-day-old plants) leaf blades except at 24-27 h incubation, at which time enriched leaves were lower in digestibility than control o nes. Enriched CO2 concentrations increased the content of acid deterge nt fiber (ADF) and cellulose of young wet leaves, Sections of main sho ots at 26 days tended to have increased digestibility with elevated CO 2 levels. Enriched CO2 concentrations did not alter the digestibility of flag leaves from 105-day-old plants or of flag leaves, uppermost st ems, and sheaths from plants at full grain maturity, Enriched CO2 leve ls reduced the acid detergent lignin (ADL) and tended to reduce the pr otein of leaves from 105-day-old plants. For mature leaf blades, neutr al detergent fiber, ADF, and cellulose were, or tended to be, higher w hile 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 th at enriched CO2 concentrations to 550 mu mol mol(-1) did not substanti ally alter wheat in vitro digestibility, regardless of irrigation trea tment. Elevated CO2 altered fiber components and protein, but these we re not consistent among parts and harvests.