Elevated carbon dioxide and temperature effects on rice yield,leaf greenness,and phenological stages duration

The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO₂]) (550 μmol mol^?1) and air temperature (+2–3 °C) on japonica rice (Oryza sativa L. “Ariete”) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO₂]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO₂] (average 382 μmol mol^?1). Results obtained showed that the rice “Ariete” had a moderate high yielding under open-field condition, but was susceptible to air temperature rise of +2–3 °C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO₂] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.     

Effect of elevated carbon dioxide (CO2) on phenolic acids,flavonoids, tocopherols,tocotrienols, γ-oryzanol and antioxidant capacities of rice (Oryza sativa L.)

There have been no studies conducted with the objective of investigating the effect of elevated CO₂ concentrations ([CO₂]) on antioxidants in grains. Therefore, a two-year field experiment was conducted using open-top chambers with two levels of atmospheric CO₂ (375 and 550 μmol/mol) to evaluate their effects on rice grain antioxidants. Following exposure to high [CO₂], the total phenolic content of all rice milling fractions decreased (3%–18%), with the highest reduction in the brown rice for sinapic acid (167%), and in the white rice for p-hydroxybenzoic acid (100%). The total flavonoid content also decreased under elevated [CO₂] in all rice milling fractions (8%–14%), with apigenin (25%) being highly affected in the white rice, and tricin (12%) in the bran. The same trend was found for γ-oryzanol, with decreases of 35%, 32%, 25%, and 2% in the white rice, brown rice, husk, and bran, respectively. In the white and brown rices, tocopherols and tocotrienols were all lower under elevated [CO₂], with reductions larger for α-tocotrienol (69%), γ-tocotrienol (46%), and α-tocopherol (38%). Good correlations between antioxidant contents and DPPH radical scavenging capacities indicated that these decreases may be meaningful in the preventive ability of rice against free radical-mediated degenerative diseases.     

Effect of Elevated Carbon Dioxide Concentration on Rice Quality: Proximate Composition,Dietary Fibers,and Free Sugars

Little is known regarding the impact of elevated carbon dioxide concentration ([CO₂]) on the chemical composition of rice grains. A field experiment was conducted with open‐top chambers with rice (Oryza sativa L. cv. Ariete) grown at two levels of atmospheric CO₂ (375 and 550 μmol/mol), and their effects were monitored on the proximate composition and carbohydrate contents of the grains. Following exposure to elevated [CO₂], soluble dietary fiber increased by 136, 82, and 77% in brown rice, white rice, and bran, respectively. Increases of a lower magnitude (8%) were observed for insoluble dietary fiber in the bran and brown rice. For all 10 sugars identified, there was a trend for increasing their content. For example, increases of 135% were recorded for glucose in the white rice. In all rice milling fractions, elevated [CO₂] reduced the protein (4–15%) and amylose (6–16%) contents, with no effect on the ash, starch, and gross energy contents. The fat content was increased by elevated [CO₂] in the white rice (23%) and tended to decrease in the bran (9%). It is concluded that besides yield, increased dietary fiber might be another positive effect of high levels of atmospheric CO₂ expected by the middle of the current century.     

Effect of Elevated Carbon Dioxide Concentration on Rice Quality: Nutritive Value,Color, Milling,Cooking, and Eating Qualities

Increase in the atmospheric carbon dioxide concentration ([CO₂]) enhanced the concentration of carbohydrates in rice grains, according to results of a previous study. However, its impact on other quality traits is little known. To investigate the effect of CO₂ levels (375 and 550 μmol/mol) on rice quality, a field experiment was conducted with open‐top chambers. Elevated [CO₂] affected several nutritional parameters of the grain. Whereas the concentration of α‐linolenic acid increased, that of linoleic and γ‐linolenic acids decreased. For example, reductions of 9 and 28% were observed for linoleic acid in the brown rice and for γ‐linolenic acid in the husk, respectively. Phytic acid concentration and zinc bioavailability were unaffected. Whereas iron bioavailability decreased in the brown rice (22%), calcium bioavailability increased in the bran and husk (5–11%). The concentrations of essential amino acids were also reduced; for example, the amount of isoleucine in the white rice, tyrosine in the brown rice, and phenylalanine in the bran decreased by 40, 57, and 23%, respectively. In contrast, elevated [CO₂] resulted in improved grain whiteness (3%) and starch viscosity (11%), with no effect on the milling quality. These data indicate that increased [CO₂] has both positive and negative effects on quality, depending on the specific end use of the rice grain.     

Some factors affecting the concentration of the aroma compound 2-acetyl-1-pyrroline in two fragrant rice cultivars grown in South China

The fragrance potential of two fragrant rice (Oryza sativa L.) cultivars grown in South China was investigated in this study using headspace SPME and static headspace in conjunction with GC-MS. About a five-fold difference of 2-acetyl-1-pyrroline (2-AP) levels were observed among the two fragrant rice cultivars, with Guixiangzhan having the highest content (3.86 μg·g⁻¹) comparable to that obtained with Thai KDML 105 rice. Other compounds instead of 2-AP were assumed to contribute to the characteristic aroma of Peizaruanxiang. The two cultivars were subjected to two preharvest treatments (planting density and harvest date) and different storage conditions (3 to 6 months at −4, 8, 20, and 30°C). Results were discussed in terms of grain yield, milling quality, grain appearance, and amylose and protein contents of rice samples associated with differing treatments. Highest 2-AP concentrations were obtained for Guixiangzhan and Peizaruanxiang with lower planting densities, the earliest harvesting time of 10 days after heading, the shortest storage time of 3 months, and the lowest storage temperature of −4°C. These findings indicate that manipulating pre- and postharvest treatments can greatly improve the specific attributes of the domestically produced cultivars. With that in mind, China could effectively increase its share of the domestic market of fragrant rice and even tap into the international market.