ENHANCED ROOT-SYSTEM C-SINK ACTIVITY, WATER RELATIONS AND ASPECTS OF NUTRIENT ACQUISITION IN MYCOTROPHIC BOUTELOUA-GRACILIS SUBJECTED TO CO2 ENRICHMENT

In order to better elucidate fixed-C partitioning, nutrient acquisitio n and water relations of prairie grasses under elevated [CO2], we grew the C-4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column-lysimeters in two growth chambers maintained at cu rrent ambient [CO2] (350 mu L L(-1)) and twice enriched [CO2] (700 mu L L(-1)). Once established, plants were deficit irrigated; growth cham ber conditions were maintained at day/night temperatures of 25/16 degr ees C, relative humidities of 35%/90% and a 14-hour photoperiod to sim ulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produc ed 35% and 65% greater total and root biomass, respectively, and had t wice the level of vesicular-arbuscular mycorrhizal (VAM) infection (19 .8% versus 10.8%) as plants grown under current ambient [CO2]. The CO2 -enriched plants also exhibited greater leaf water potentials and high er plant water use efficiencies. Plant N uptake was reduced by CO2 enr ichment, while P uptake appeared little influenced by CO2 regime. Unde r the conditions of the experiment, CO2 enrichment increased root biom ass and VAM infection via stimulated growth and adjustments in C parti tioning below-ground.