Growth and nitrogen uptake of CO2-enriched rice under field conditions

The effects of elevated CO2 are reported here on the uptake of nitrogen (N) and its relationships with growth and grain yield in rice (Oryza sativa). Using free-air CO2 enrichment (FACE), rice crops were grown at ambient or elevated (c. 300 mu mol mol(-1) above ambient) CO2 and supplied with tow, medium or high levels of N. For the medium and high N treatments, FACE increased N uptake at panicle initiation but not at maturity. For total dry matter, as well as spikelet number and grain yield, positive interactions between CO2 and N uptake were observed. Furthermore, spikelet number was closely associated with N uptake at panicle initiation. These results indicate that, to maximize rice grain yield under elevated CO2, it is important to supply sufficient N over the whole season, in order to maintain the enhancement in dry matter production. In addition, N availability must be co-ordinated with the developmental stage of the crop, specifically to ensure that sufficient N is available at panicle initiation in order to maximize spikelet number and grain yield.