The impact of free-air CO2 enrichment (FACE) and nitrogen supply on grain quality of rice

Because CO2 is needed for plant photosynthesis, the increase in atmospheric CO2 concentration ([CO2]) has the potential to enhance the growth and yield of rice (Oryza sativa L.), but little is known regarding the impact of elevated [CO2] On grain quality of rice, especially under different N availability. In order to investigate the interactive effects of [CO2] and N supply on rice quality, we conducted a free-air CO2 enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001-2003. A long-duration rice japonica with large particle (cv. Wuxiangging 14) was grown at ambient or elevated (ca. 200 mu mol mol(-1) above ambient) [CO2] under three levels of N: low (LN, 15 g N m(2)), medium (MN, 25 g N m(2)) and high N (HN, 35 g N m(2) (2002, 2003)). The MN level was similar to that recommended to local farmers. FACE significant increased rough (+12.8%), brown (+13.2%) and milled rice yield (+10.7%), while markedly reducing head rice yield (-13.3%); FACE caused serious deterioration of processing suitability (milled rice percentage -2.0%; head rice percentage -23.5%) and appearance quality (chalky grain percentage +16.9%; chalkiness degree +28.3%) drastically; the nutritive value of grains was also negatively influenced by FACE due to a reduction in protein (-6.0%) and Cu content (-20.0%) in milled rice. By contrast, FACE resulted in better eating/cooking quality (amylose content -3.8%; peak viscosity +4.5%, breakdown +2.9%, setback -27.5%). These changes in grain quality revealed that hardness of grain decreased with elevated [CO2] while cohesiveness and resilience increased when cooked. Overall, N supply had significant influence on rice yield with maximum value occurring at MN, whereas grain quality was less responsive to the N supply, showing trends of better appearance and eating/cooking quality for LN or MN-crops as compared with HN-crops. For most cases, no [CO2] x N interaction was detected for yield and quality parameters. These data suggested that the current recommended rates of N fertilization for rice production should not be modified under projected future [CO2] levels, at least for the similar conditions of this experiment. (c) 2007 Published by Elsevier B.V.