The impact of free-air CO 2 enrichment (FACE) and nitrogen supply on grain quality of rice

Abstract

Because CO 2 is needed for plant photosynthesis, the increase in atmospheric CO 2 concentration ([CO 2]) has the potential to enhance the growth and yield of rice ( Oryza sativa L.), but little is known regarding the impact of elevated [CO 2] on grain quality of rice, especially under different N availability. In order to investigate the interactive effects of [CO 2] and N supply on rice quality, we conducted a free-air CO 2 enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001–2003. A long-duration rice japonica with large panicle (cv. Wuxiangging 14) was grown at ambient or elevated (ca. 200 μmol mol −1 above ambient) [CO 2] 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 [CO 2] 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 [CO 2] × 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 [CO 2] levels, at least for the similar conditions of this experiment.