Abstract: 【Objective】 In order to investigate the effect of atmospheric CO2 concentration ([CO2]) on grain-filling properties of rice. 【Method】Using the unique free-air CO2 enrichment (FACE) system in China, a japonica rice cv. Wuxiangging 14 was grown at ambient or elevated (ca 200 μmol mol-1 above ambient) [CO2] under three levels of N: low (LN, 150 kg hm-2), medium (MN, 250 kg hm-2) and high N (HN, 35 kg hm-2). Grain filling dynamic at different positions of rice panicle was investigated. The Richards equation was used to describe grain filling processes. 【Result】(1) Under LN condition, FACE treatment increased grain weight significantly, averaging 9.9%, 7.0% and 7.7% for grains on upper, middle and low parts of the panicle, respectively. However, no effect of FACE was observed under HN and MN conditions. (2) In general, FACE treatment enhanced the initial relative growth power (GR0/W0) of grains on different parts of the panicle. (3) FACE treatment greatly increased the maximum grain-filling rate (MRm), averaging 38.6%, 24.3% and 38.6% for LN-, MN- and HN-plants, respectively, with CO2-induced increase being larger for upper grains than middle and low ones on the panicle. In addition, the mean grain-filling rate (MGR) was enhanced due to FACE by 38.9%, 47.7% and 44.1% for LN-, MN- and HN-plants, respectively. (4) Overall, grains of FACE plants had later time to reach maximum growth rate, heavier grain weight at time when the growth rate is maximum and shorter mean grain-filling duration as compared with those of ambient plants. As for different grain-filling stages, FACE treatment obviously prolonged the duration of early grain-filling stage, while the duration of middle and late grain-filling stages showed the opposite trends.【Conclusion】These data indicated that FACE treatment increased the GR0/W0, GRm and MGR, prolonged the duration of early grain-filling stage with a shortening of duration of middle, late and whole grain-filling stages. FACE treatment greatly increased grain weight of different panicle positions under LN condition, whereas no significant changes were observed under MN and HN conditions.

Key words: Rice, Free-air CO2 enrichment (FACE), Grain filling property