Monday, 6 October 2008
George R. Brown Convention Center, Exhibit Hall E
Adequate N status in plants is a critical factor for ensuring their ability to respond positively to elevated atmospheric CO2 concentrations ([CO2]). A cultivar with higher N concentration might thus respond better to elevated [CO2]. To test this hypothesis, we examined four rice cultivars with different times to maturity in a 2-year free-air CO2 enrichment (FACE) experiment. Plant N concentration at the heading stage differed significantly between cultivars but without any significant [CO2] ´ cultivar interaction; cultivars that matured earlier had higher N concentrations. Grain yield was significantly increased by elevated [CO2] (by up to 23%), but the magnitude differed among the cultivars due to a significant [CO2] ´ cultivar interaction; two cultivars (one with early and one with late maturity) responded more strongly to elevated [CO2] than those with intermediate maturity dates, resulting from increased spikelet density. Biomass and N uptake at the heading stage were closely correlated with grain yield and spikelet density. Our 2-year field trial rejected the N-response hypothesis and showed that the magnitude of the growth enhancement before heading rather than plant N concentration is a useful criterion for selecting cultivars capable of adapting to future elevated levels of [CO2].