Physiological Response Of Rice Seedlings To Elevated CO₂ Concentration And Water Stress

Based on the widespread fact of global CO₂ concentration increases and water stress, as well as the understanding of cultivating CO₂ “fertilization effect”, the rice（Oryzaglaberrima）liao star 1 is studied. At the atmospheric CO₂ concentration conditions（380 ± 10 μmol/mol） and at high CO₂ concentration conditions（760 ± 20 μmol/mol）, PEG 6000 was used to simulate rhizosphere water stress（PEG6000 concentration is 0%, 5%, 10%, 5%）. Growth, photosynthetic parameters, antioxidant enzyme activity, and osmotic adjustment substances contents of rice seedling under elevated CO₂ and/or different water stress were studied to provide important theoretical basis.The results showed as follow:1.Compared with the control, the growth of rice seedlings was inhibited by the single water stress, a significant reduction in the plant height and root length, fresh weight and dry weight were detected, and the inhibition of the ground portion is greater than the underground part, the inhibition of the fresh weight is greater than dry weight; Under a single water stress, net photosynthetic rate（Pn）, stomatal conductance（gs） and transpiration rate（Tr） were significantly decreased compared with the control. Under light and moderate water stress, intercellular CO₂ concentration（Ci） decreased, decrease of Pn was largely because of stomatal factors, But under severe water stress, Ci increased, decrease of Pn was largely because of non-stomatal factors; The chloroplast pigment content, the initial fluorescence yield（Fo）, the largest PSII photochemical quantum yield（Fv/Fm） and potential photochemical efficiency（Fv/Fo） do not change significantly under mild water stress; Fo does not change significantly under moderate water stress and Fo was significantly increased under severe water stress. Under moderate and severe water stress, Fv/Fm, Fv/Fo and Chla, Chlb, Car contents were significantly decreased; Under light water stress POD and Pro content increased, and no significant change detected in MDA content, compared with control. Membrane lipid peroxidation increased significantly under moderate and severe water stress, and content of soluble sugar（SS）, proline（Pro）, soluble protein increased. Under moderate water stress, SOD and POD activities increasd and under severe water stress SOD activity increasd, The CAT activity has no significant change under water stress.2. High CO₂ concentration promote the growth of rice seedlings, a significant increases in plant height and root length, the promotion on root is greater than plant height, dry weight of underground part increased significantly and the promotion on dry weight is greater than fresh weight; Pn was increased significantly and gs, Tr, Ci were decreased significantly under high CO₂ concentration compared with control. And photosynthesis was also increased by the increase of Fv/Fm, Fv/Fo and Chla, Chlb, Car content. High CO₂ concentration could increase POD, CAT activity to clear reactive oxygen, significantly reduce membrane permeability, and the increases of SS and soluble protein contents may be the results of accelerated metabolism of carbohydrates and protein.3. Under high CO₂ and water stress, high CO₂ promoted the growth of rice seedlings compared with under the atmospheric CO₂ concentration, Pn, gs and Tr were also significantly increased under water stress. Photosynthesis was promoted by the increases of Fv/Fm, Fv/Fo and content of chlorophyll and decrease of Fo to reduce damage induced by water stress. The decrease of Pn was because of stomatal factors from non-stomatal factors unde severe water stress. High CO₂ concentrations could also alleviate danmage of membrane caused by water stress, reduced the peroxidation of membrane lipid and membrane permeability, and increased activities of SOD, POD, CAT to clear reactive oxygen species. Water stress was more severe, the alleviation was more obvious. The increase of soluble protein content was for osmotic adjustment under a certain degree of water stress. Key words: rice, elevated CO concentration, water stress, physiolo-...