Yield formation of CO2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice (Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO2] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO2 enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol−1) [CO2] under two levels of supplemental N (12.5 g Nm−2 and 25 g Nm−2). Elevated [CO2] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO2] was independent of N fertilization, but varied among different years. On average, elevated [CO2] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO2], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO2], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO2] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO2] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO2] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO2] levels.