The impact of free-air CO2 enrichment (FACE) and N supply on yield formation of rice crops with large panicle

Because CO2 is needed for plant photosynthesis, the increase in atmospheric [CO2] has the potential to enhance the growth and yield of agricultural crops. However, little is known about the interactive effects of elevated [CO2] and nitrogen (N) supply on grain yield formation of rice (Otyza sativa L.), and no information is available on the combined effect of these factors on grain yield formation of rice cultivars with large particles or under high N supply. Therefore we conducted a free-air CO2 enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001-2003. A japonica cultivar with large particle (Wuxiangging 14) was grown at ambient or elevated (c. 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 significantly increased the grain yield by 12.8% across the 3 years. Maximum grain yield was reached by MN-crops under both ambient and FACE treatments. FACE also substantially increased particle number per square meter (+18.8%) due to the increase in maximum tiller number (+30.0%) being substantially more than the decreases in productive tiller ratio (-7.7%) with FACE: the former was related to significant increases with FACE in tillering occurrence speed from 10 to 30 days after transplanting (DAT), while for the latter the increases in tillering extinction speed after 45 DAT contributed to the decreases. FACE significantly reduced spikelet number per particle (-7.6%), which was due mainly to the significant increase in degenerated spikelets per panicle (+51.7%) while differentiated spikelets per particle showed no change. FACE caused a small but significant increase in filled spikelet percentage and grain weight, which may be due to the combined effects of increased proportion of spikelets on primary branches and source-sink ratio at heading under FACE conditions. The year effects were all significant for yield and its components; however, interactions between all treatment variables were hardly detected. For the cultivar and conditions of this experiment, the above results indicate that, in addition to supply proper total amount of N over the whole season, high-yielding cultivation under future elevated [CO,] conditions need to be focused on regulations after particle initiation in order to increase the productive tiller ratio, enhance the spikelet formation and raise harvest index. (c) 2006 Elsevier B.V. All rights reserved.