Effect Of Increasing CO₂ Concentration On Growth, Physiology, Yield And Quality Of Rice

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. With the global atmospheric CO₂ concentrations of the growing increase, rice yields will be certain changes in its growth, yield and nutrient absorption and utilization will be corresponding changes.Through the open-top chamber control atmospheric CO₂ concentration, we research on rice growth and development, and Physiological characteristics such as yield and quality, and height, length of panicle, the net photosynthetic rate, transpiration, water use efficiency, productivity and yield components, chlorophyll content, protein and amino acid content, and their responses to elevated CO₂ were analyzed. The results showed that, compared with CK, the height in maturation stage increased from 5.82% to 11.76%,the length of panicle from7.02% to 12.40% under two high CO₂ concentration (550μmol·mol^-1and 750μmol·mol^-1).Net photosynthetic rate in rice jointing stage changes on a single peak, the highest 9:00 am, the lowest level in around 13:00, midday depression of photosynthesis is more obvious, but with the increasing atmospheric CO₂ concentrations, midday depression of photosynthesis have been alleviated, When CO₂ increased to 750μmol ? mol^-1, midday depression of photosynthesis disappeared. Rice leaves the stomatal conductance is a single peak-evident, the highest 10:00 am, stomatal conductance around 14:00 in the reduction of the most significant. At each stage of fertility, with the increase of CO₂ concentration, stomatal conductance decreased, the largest drop in jointing stage, the smallest in tillering stage.Two high concentration of CO₂ processing and background showed the biggest transpiration rate in heading stage, followed by jointing stage, tillering stage relatively small trend. Through the various growth stages of the transpiration rate variance analysis and multiple comparison indicates that the CO₂ concentration of different treatment under various stages of rice transpiration rate of the overall difference reached significant levels. In the same CO₂ concentration, water use efficiency as the rice growing period and the post was generally higher trend. When the atmospheric CO₂ concentration from 350μmol ? mol^-1 to 750μmol ? mol^-1, in different developmental stages of rice, water use efficiency increases ranging from water use efficiency in the maturation stage the biggest increase, respectively 35.24 % and 77.05%.In elevated atmospheric CO₂ scenarios, chlorophyll a, b and the total amount of chlorophyll has increased , and promote the strengthening of rice photosynthesis. The concentration of CO₂ in the 550μmol ? mol^-1and750μmol ? mol^-1, the jointing stage of chlorophyll-a more than the current (350μmol ? mol^-1) increased by 4.65%and7.94%, chlorophyll b increased 16.03%and20.75%, The total amount of chlorophyll increased 7.22 %and 10.83% in atmospheric CO₂ concentration increased the circumstances, the rice leaves the content of carotenoids also an upward trend, increased by 17.81 %and 35.61 %.With the increasing in atmospheric CO₂ concentration, the rice yield give an upward trend. With the background CO₂ concentration (350μmol·mol^-1) compared to two high CO₂ concentrations, the yield increased by 19.34 percent and 31.55 percent. With the increase in atmospheric CO₂ concentration , the most notable contribution on increase rice yield factor is the improvement of grains per panicle.The second is thousand seeds weight.The total grains per panicle is minimum.With the increasing atmospheric CO₂ concentrations, the nutritional elements in rice, such as phosphorus, potassium and copper content with the atmospheric CO₂ concentration was increased gradually reduce the trend, which, phosphorus and potassium content of the most significant decrease, while copper content is the largest decline, reaching 13.79 percent and 26.09 percent; On the other hand, the increase in atmospheric CO₂ concentration, rice grain in sodium, zinc, selenium and manganese content are in a growth trend, rising more of the elements for sodium and manganese, and manganese content is also the largest increase, reaching 4.58 percent and 7.09 percent, while calcium, magnesium and iron in rice grain are no change in the trend obviously.Compared with the background atmospheric CO₂ concentration, when CO₂ increased to 550 and 750μmol·mol^-1, protein content of a declining trend, were down 3.10 percent and 5.49 percent. The overall differences in protein content also reached a significant level. This is due to the growth environment of the increase in CO₂ concentration, increased use of rice to carbon, causing its grain carbon and nitrogen in the balance between change and crops need to absorb more from the soil of nitrogen to meet their growing needs.In the production practice, we must be appropriately increased use of nitrogen fertilizer. With the increasing atmospheric CO₂ concentrations, the amino acid components in rice decreased, tryptophan and Histidine dropped mostly, isoleucine and leucine are the smallest rate of decline.With the increasing in atmospheric CO₂ concentration, total amino acids and essential amino acids showed overall downward trend. When atmospheric CO₂ concentration are 550 and 750μmol·mol^-1, compared with the background, the tested rice grain decreased the total content of amino acids 5.99% and 14.26% respectively, and the total content of 8-essential amino acids dropped by 5.33 percent and 12.53 percent. Increased in atmospheric CO₂ concentration on rice methionine and threonine content appropriate to increase the role-played. Therefore, although the high atmospheric CO₂ concentration would cause a decrease of rice protein content, but some of the amino acid increased, thus can improved the composition of the rice protein structure furtherly.