Carbon dioxide and temperature effects on forage establishment: tissue composition and nutritive value

Atmospheric CO2 concentration ([CO2]) and temperature are likely to increas e in the future and may change plant growth and composition characteristics . Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flugge) were grown on a natural field soil in temperature-gradient greenho uses to evaluate the effects of elevated [CO2] and temperature on tissue co mposition and digestibility during the establishment year. Carbon dioxide l evels were maintained at 365 (ambient) and 640 mu L CO2 L-1 air. The temper ature-gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 degrees C above ambient. Samples were taken of p reviously undefoliated herbage at 57, 86, 121, 148, and 217 days after plan ting and entire plots were harvested at 218 days after planting. Elevated [ CO2] increased total nonstructural carbohydrate concentration in rhizoma pe anut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO2]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO2], while the N concentration in ba hiagrass was not affected by temperature or [CO2]. No effects of [CO2] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO2] increased neutral detergent fibre in bahi agrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg(-1)) than at elevated [CO2] (609 g kg(-1)). Elevated [CO2] had a greater effect on tissue composition of rh izoma peanut than of bahiagrass. These data suggest that elevated temperatu re and CO2-induced changes in chemical composition of forage species adapte d to humid subtropics will be relatively small, particularly for C4 species .