| Grain output of rice occupies over 40 percent of total food production in China, and stabilizing and increasing rice production are of vital importance in assuring the security of Chinese food supply. Facing the continuous increase of the concentration of atmospheric CO2, we have to answer such important questions imminently: How does rice yield response to this change? How does this change influence rice growth, development and nutrient utilization? And, what measures we can take to cope with the effect of the atmospheric CO2 elevation on rice production? Free-Air CO2 Enrichment, FACE, is designed to elevate CO2 concentration under field condition with no isolation and least disturbance to natural environment. CO2 flows freely and its concentration is computer-controlled so that plants growing within the FACE rings are always supplied with air of the desired CO2 concentration and their growth condition, both above- and underground, is well consistent with natural environment. Therefore, it is generally agreed that FACE approach is the most realistic of the techniques currently employed to create higher-than-normal concentrations of atmospheric CO2 in order to study the impacts of CO2-enriched air on plant growth and development. This study was carried out in the platform for FACE study, located in Wuxi (31 37'N, 120 28'E), China, using Wuxiangjing 14 as tested rice cultivar. The CO2 concentration in FACE treatment was 570umol mol-1, with 370umol mol-1 as ambient (CK). Nitrogen application rates were 150, 250 kg N-ha'1 in 2001, and 150, 250, 350 kg N-ha-1 in 2002 and 2003, respectively. The main purpose of the experiment was to study the impacts of the elevation of global atmospheric CO2 on rice production in rice-wheat ecosystems in China. Results showed as follows:1. Compared with CK, the duration from sowing to heading, and from heading tomaturity of shortened 3.5 and 2.3 days, respectively, while the whole growth duration shrank 5.8 days in FACE treatment. Change of growth duration in FACE treatment was greater and more susceptive of the environment than that in CK. Multiple regression and path analysis indicated that the reduction of growth duration was closely related to the obvious decrease of N content in rice plant in N-n, jointing, and heading stages, and increase of P content in rice plant and concentration of soluble carbohydrates in stem and sheath in heading and maturity.2. In three year's experiment, FACE significantly affected rice yield. Compared with CK, Grain output in FACE treatment increased 1275.0 (12.04), 1360.0 (14.05), and 1163 (13.60) kg.ha-2 (percent) in 2001, 2002 and 2003, respectively. Suitable rate of N applied (250 kg N.ha-2) significantly increased rice yield in FACE, while over-rated N (350 kg N.ha-2) reduced the yield. Number of panicles, filled grain percentage and 1000-grain-weight in FACE, average value of the data in 2001, 2002 and 2003, increased 18.07, 4.79 and 1.31 percent, respectively, while number of spikelets per panicle decreased in FACE treatment. FACE significantly influenced number of panicles and number of spikelets per panicle. The effects of FACE and N application on rice yield and its components were independent and no significant interaction between FACE and N was found in this study.3. Tillering speed between 11th and 30th day after transplantation and the highest tiller number was significantly higher in FACE treatment than that in CK, which led to the significant increase of panicle number. The differentiation of spikelets was not affected by FACE, but degeneration of the spikelets on secondary branches significantly increased in FACE, which contributed the decline of spikelet number per panicle in FACE treatment.4. FACE significantly increased the biomass production and had no apparent influence on economic coefficient. The differences of biomass production during various stages between FACE and CK were significant, but the tendency and degree of effects of FACE on biomass accumulation were different with growth period. The biomass accumulated...
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