The Effects Of Elevated CO₂ To Different Tillering Positions On Rice Growth, Yield And Quality-A FACE Study

The atmospheric carbon dioxide concentration ([CO2]) has increased from less than 280 μmol mol-1 in preindustrial times to the current 396 μmol mol-1, it will reach 550 μmol mol-1 in 2050 according to several prediction models. Rice (Orayza Sativa L) is one of the most important sources of food. Although the effects of high [CO2] on rice growth, yield and quality have been extensively reported, whether such effects various with different tillering positions are unclear. In order to answer this question, A FACE (Free Air gas Enrichment) experiment was conducted in a rice field located in Yangzhou China in 2013. Two Chinese rice cultivars, Wuyunjing23 (WYJ23, conventional Japonica rice) and II you 084 (ⅡY084, super rice), were grown at Ambient [CO2] and Elevated [CO2](200 μmol mol-1 above Ambient). The effects of elevated atmospheric [CO2] on growth, yield and quality of rice at different tillering positions were investigated for the first time, the results obtained from this study will provide new experimental evidence for developing rice adaptation strategies to cope with the changing climate.1.Compared to the control (Ambient [CO2]), elevated [CO2] increased the leaves, stems, panicles and aboveground dry weight of ⅡY084 at maturity by 29%**,31%*,47%* and 40%*, respectively. WYJ23 showed no significant change on dry matter production and distribution. Week CO2 by variety interactions (p<0.1) were detected for the dry weight of individual organs as well as the total aboveground dry weight. Averaged after classification, the dry weight increase by elevated [CO2] of panicles and aboveground biomass of the primary tillers (50%**,42%**) was greater than the secondry tillers (40%+,37%*) of ⅡY084; While the dry weight increases of leaves and stems were the same for the primary and secondry tillers (30%). On the controry, the CO2 response of the secondry tillers (11%*、9.4%*、8%*) was greater than the primary tillers (non significant) for WYJ23. A week interaction between CO2 and variety on dry weight of different organs were detected for the most of primary tillers.2. The fertilizer effect of elevated CO2 to the grain yield of ⅡY084 was significantly greater than WYJ23, which was showed by the significant CO2 by variety interaction:compared to the control, elevated CO2 increased grain yield of 397 (61%**) and 83 g m-2 (12%*) for ⅡY 084 and WYJ23, respectively. Averaged after classification, FACE increased the grain yield of main stem, primary tillers and secondry tillers of ⅡY084 for 47,233 and 117 g m-2, the increasement was 50%*,64%** and 62%*, respectively. While for WYJ23 the increasement was 7 g m-2 (8%ns),27 g m-2 (7%+) and 49 g m-2 (25%+). Based on different tillering positions, CO2-induced yield enhancement of Ⅱ Y084 reached significant level (P＜0.1) for the tillering positions 6/0,7/0,8/0,9/0,1/6, while for WYJ23 only tillering position 6/0 showed significant increase in grain yield by elevated CO2. Variance analysis showed that, the interactions between CO2 and variety on grain yield reached significant level (P＜0.1) for the main stem, tillering positions 6/0,7/0,8/0,9/0,10/0 and 1/8.3. Compared to the control, elevated CO2 increased spikelets per panicle, spikelets per unit area, fulfilled grain percentage and fulfilled grain weight of ⅡY084 by 28%+,37%*,11%** and 6%*, respectively; But for WYJ23, only spikelets per unit area (10%) and fullfilled grain weight (2%) has increased significantly. The interactions between CO2 and variety on spikelets per panicle, spikelets per unit area, fulfilled grain percentage and fullfilled grain weight reached or close to 0.1 significant level. Averaged after classification, the CO2-response of primary tillers (32%**,41%**,11%**) was greater than secondry tillers (21%ns,34%+,12%*) on the spikelets per panicle, spikelets per unit area, fulfilled grain percentage, but the fullfilled grain weight showed the opposite trend (5%+ vs.8%*) for ⅡY084. On the controry, CO2 elevation had no significant effects on each yield components of main stem, primary tillers and secondry tillers of WYJ23. The interactions between CO2 and variety on spikelets per panicle, spikelets per unit area and fulfilled grain percentage reached P<0.1 for the most of primary tillers.4. Elevated CO2 increased primary branch number, grains on the primary branch and panicle length of ⅡY084 by 9%**,28%** and 10%+, respectively, but only panicle length (7%**) was increased significantly for WYJ23. The interactions between CO2 and variety on primary branch number, grains on the primary branch and grain density reached or close to 0.1 significant level. Averaged after classification, the CO2-response of primary tillers (11%**,30%**, 14%**,17%+) was greater than secondry tillers (7%*、24%**、8%ns、12%ns) on primary branch number, grains on the primary branch, panicle length and grain density of ⅡY084, but most of the panicle traits of WYJ23 showed opposite trend. The interaction between CO2 and variety on grains on the primary branch and panicle length reached or close to 0.1 significant level for the most of primary tillers.5. Elevated CO2 increased milled rice percentage (3%+) and head rice percentage (8%+), but decreased chalky grain percentage (30%+), chalkiness area (23%*), chalkiness degree (46%**), total starch content (6%+), amylopectin content (12%), gel consistency (23%) and N concentraitions (13%+). In terms of WYJ23, elevated CO2 increased chalky grain percentage (57%*), chalkiness degree (67%*), gel consistency (9%*) and Zn concentraitions (9%+), but decreased the concentraitions of N (13%**) and Mg (16%+).The interactions between CO2 and variety on milled rice percentage, head rice percentage, appearance quality, total starch content, amylopectin content, gel consistency and Mg concentraitions reached or close to 0.1 significant level. Averaged after classification, the CO2-response of primary tillers was greater than secondry tillers on chalky grain percentage, chalkiness area and N concentraitions of ⅡY084, but milled rice percentage, chalkiness degree, total starch content, amylopectin content and gel consistency showed opposite trend. The CO2-response of secondry tillers was greater than primary tillers on brown rice percentage, milled rice precentage, head rice percentage, chalky grain percentage and chalkiness degree of WYJ23, but gel consistency, the concentraitions of N, Mg and Zn showed the opposite trend. The CO2 by variety interactions were significant for total starch content and amylopectin content of the most of the secondry tillers, and for processing quality, appearance quality, and gel consistency of the most of tillers.In conclusion, in most cases the effects of elevated CO2 on rice growth, grain yield and quality varied with different tillers or variety. The CO2 response of primary tillers was greater than secondry tillers on rice growth and grain yield for ⅡY084, but the response of WYJ23 showed the opposite trend. The CO2 by variety interactions on rice growth and yield traits were detected for the most of primary tillers. The response of the hybrid rice to elevated CO2 was significantly greater than conventional rice. Elevated CO2 improved processing quality and appearance quality of the most of tillers of hybrid rice, but the conventional rice showed the opposite trend. In most cases, the CO2 by variety interactions were significant for total starch content and amylopectin content of the most of the secondry tillers, and for processing quality, appearance quality, and gel consistency of the most of tillers.