Effects Of Free-air CO₂ Enrichment (FACE) On Rice Quality And Primary Research On Its Formation

Effects of free-air CO2 enrichment (FACE) on rice quality was investigated with two rice cultivars: Asominori (Japonica) and International Rice24(Indica) over two cropping seasons(2003 and 2004). According to the results from last two years, the mechanism of effect of FACE on the quality was studied with another rice cultiar: Wu xiangjing-14(Japonica) in 2004.The quality of rice grains harvested from the control(ambient CO2: 370μmol/mol) and FACE treatment( ambient CO2: 570μmol/mol) was studied. FACE decreased significantly the rates of brown rice, milling rice and heading milled rice from 82.25%, 71.94%,63.70% to 80.76%,70.65%, 62.05% for IR24(International Rice 24) and from 83.85%,73.04%,70.65 to 83.30%,72.20%,69.10% for ASO(Asominori) respectively. FACE had no obvious effect on the length, width and length-width ratio of rice grains. But there were significant decreases in chalky rice grain rate under FACE conditions, by 36.11% and 19.57% for IR24 and ASO respectively. The amylose content was not obviously affected by FACE treatment, but the peak viscosity, breakdown, setback and pasting temperature from the RVA profile responded markedly different between FACE and control. The peak viscosity increased obviously in both experimental years for two cultivars, but the other three parameters didn't changed consistently as a result of difference between years and other environmental factors. The content of crude protein as an important parameter for rice quality was decreased significantly under the FACE environment, from 11.77 % to 10.23% for IR24 and from 10.97 to 9.91% for ASO.Studies on the grain-filling of Wuxiangjing-14 showed that rice growing under the FACE environment accumulated more carbohydrate, but decreased the content of totle nitrogen based on dry mass in the vegetative tissues. From heading to 12 days after anthesis,carbohydrate was accumulated as a result of unestablishment of sink capacity of grain under both treatment but higher under control conditions.From 12 days after anthesis, the contents of carbohydrate in the vegetative tissues were declined. Comparing to the control, the declining period was 6 days longer under FACE condition. No difference wasobserved about the dynamic changes of totle nitrogen basesd on dry mass between the two treatments during the whole grain filling period It suggested that the reasonable process of grain filling under FACE condition resulted in the significant decrease of chalky rice grain.Studies also showed that FACE treatment didn't affect the starch content of grain at each stage of grain filling, but the content of water soluble carbohydrate was significantly affected at the early stage of grain filling. From 12 days after anthesis to the period when the content of water soluble carbohydrate (WSC) was unchanged, the accumulation of starch under control was significantly promoted as a result of much more decline of WSC comparing to FACE treatment.. The study also made clear that FACE treatment significantly decreased the crude protein content of rice grain based on dry mass at every stage of grain filling,In conclusion, the change of milling quality of variety Wu xiangjing-14 under FACE treatment may be connected with the physiological changes in aleurone(data not showed in this paper); the change of chalky rice rate may be the result of stable process of grain filling. The increase of amylose content may be the result of large amount of carbohydrate accumulation under the FACE treatment; The actual amylose content and the structure of starch should be investigated to explain the complex changes of parameters from the RVA profile, and the lack of N assimilation may directly lead to the decrease in the content of crude protein in rice grains.