What was done
The authors grew rice (Oryza sativa) in a FACE experiment that subjected plants to atmospheric CO2 concentrations of 390 and 690 ppm throughout the growing season.  In addition, plants were supplemented with low, medium, and high rates of nitrogen application to determine the interactive effects of elevated CO2 and nitrogen on root nitrogen uptake and grain yield.

What was learned
Elevated CO2 enhanced crop nitrogen uptake by 2, 15 and 23% in the low, medium and high nitrogen treatments, respectively.  With greater amounts of nitrogen uptake, CO2-enriched plants had more raw materials available to support enhanced biomass production, which led to total dry mass enhancements of 38-45%.  Atmospheric CO2 enrichment also positively impacted final grain yields, which were 2, 15 and 23% greater in the low, medium and high nitrogen treatments, respectively.

What it means
As the atmospheric CO2 concentration rises, it is likely that rice plants will increase their nitrogen uptake and utilize this important mineral resource to enhance their biomass production and grain yield, even under conditions of low soil nitrogen availability.  However, if more nitrogen is available to rice plants, it is likely that CO2-induced yield increases will be even greater.  Thus, one can anticipate that yields of this important food crop will increase in future years, enabling the sustenance of greater human populations in areas where rice is utilized as a staple food crop.