[Effects of elevated atmospheric CO₂ concentration on chemical composition of rice straw]

Rice straw is a potential material for bioenergy production. Elevated atmospheric carbon dioxide (CO₂) concentration changed the quantity and quality of rice straw, thus changing its bioenergy production potential. In this experiment, we collected rice straw from China Free Air CO₂ Enrichment Platform (FACE). Three rice varieties, Wuyunjing 27, Y Liangyou 900 and Nipponbare N16, were selected from the FACE platform (the CO₂ concentration in the experimental group was controlled at 570 μmol ·mol^-1, which was 200 μmol ·mol^-1 higher than the control group), the chemical composition of which was analyzed. The results showed that elevated CO₂ concentration significantly increased C content, C/N, and the content of non-structural carbohydrates in straw. Elevated CO₂ concentration significantly increased total sugar release by 8.8%, 6.7% and 9.9% in Wuyunjing 27, Y liangyou 900 and N16, respectively. Elevated CO₂ concentration significantly enhanced the biomass of N16 straw, but had no effect on the straw biomass of the other two rice varieties. The total sugar yield of N16 increased most significantly with elevated CO₂ concentration, reaching 19.2%. Our results indicated that elevated CO₂ concentration could improve the quality and quantity of rice straw, thereby increasing the utilization potential of biofuel.