Quality Responses Of Twelve Rice Cultivars To Elevated Atmospheric CO₂ Concentration-a FACE Study

Global atmospheric carbon dioxide concentration [CO2] continues to rise since the industrial revolution and it is estimated that atmospheric [CO2] will increase to at least 550μmol mol-1 by 2050. Rice is the most important food crop in the world. However, there is little informaiton to date regarding genotypic variation in responsiveness of rice quality to elevated [CO2]. In order to investigate the effects of elevated [CO2] on processing quality, appearance quality, cooking and eating quality, nutritional quality and microelements concentration of different rice genotypes, we conducted a unique Free-Air CO2 Enrichment (FACE) experiment at Jiangdu County, Jiangsu Province, China (32°35′5″N, 119°42′0″E), in 2008-2009. Twelve rice cultivars, including four conventional japonica cultivars, four conventional indica cultivars and four hybrid rice cultivars, were grown under two levels of [CO2] (ambient and elevated by 200μmol mol-1). The results obtained here could provide important implications on rice breeding under future elevated [CO2] conditions. The main findings are as follows:1. Averaged across all cultivars tested, elevated [CO2] decreased head rice rate by 2% (P < 0.01), while no significant CO2 effect was observed for brown and milled rice rate; There was a significant interaction between CO2 and cultivar for head rice rate with no interaction found for brown and milled rice rate; No CO2×year interaction was detected for above parameters.2. Averaged across all cultivars tested, elevated [CO2] significantly increased chalky grain percentage, chalkiness area and chalkiness degree by 11%, 15% and 25%, respectively; There was a significant interaction between CO2 and cultivar for chalky grain percentage and chalkiness degree with no interaction found for chalkiness area; No CO2×year interaction was detected for above parameters.3. Averaged across all cultivars tested, elevated [CO2] increased amylose content and gel consistency all by 3% ( P < 0.01 and P < 0.05), decreased protein content by 7% (P < 0.01), while no significant CO2 effect was observed for gelatinization temperature; No CO2×cultivar interaction was detected for above parameters; There was a significant interaction between CO2 and year for amylose content and protein content with no interaction found for gel consistency and gelatinization temperature.4. Averaged across all cultivars tested, elevated [CO2] significantly increased peak viscosity, breakdown and final Viscosity by 3%, 5% and 1%, respectively, decreased setback by 8%, while no significant CO2 effect was observed for hot paste viscosity, consistency and peak time; There was a significant interaction between CO2 and cultivar for peak viscosity, breakdown, setback and consistency with no interaction found for hot paste viscosity, final Viscosity and peak time; No CO2×year interaction was detected for above parameters.5. Averaged across all cultivars tested, elevated [CO2] significantly decreased Cu content (-5%), while no significant CO2 effect was observed for Fe, Mn, Zn, K and Mg content. There was a significant interaction between CO2 and cultivar for Mn, K and Mg content with no interaction found for Cu, Fe and Zn content; There was a significant interaction between CO2 and year for Zn content with no interaction found for Cu, Fe, Mn, K and Mg content.