Physiological Response Of Rice Seedlings To Elevated CO₂ Concentration And/or Pb Stress

Based on global CO₂ concentration increases and Pb pollution stress in the soil,the rice seedlings?Oryza sativa L.??bei jing 2?were studied.At the atmospheric CO₂ concentration conditions?400±20?mol/mol?and at high CO₂ concentration conditions?800±20?mol/mol?,Pb?NO₃?₂ was used to simulate Pb stress,Pb?NO₃?₂ concentration is 0,50,150?M.Treatment was divided into control?AC?,high concentration of CO₂?EC?,different concentration of Pb treatment?L,H?,high concentration of CO₂ and Pb composite treatment?EC+L,EC+H?,a total of 6treatment groups.Growth,photosynthetic parameters and endogenous hormones of rice seedlings were studied to explore physiological and metabolic responses under elevated CO₂ and/or different Pb stress,which provided theoretical basis for exploring how rice responds to the change of double environmental factors of high concentration of CO₂ and Pb pollution and agricultural production in the future environment.The results show:1.Compared with AC,sigle Pb stress inhibited the growth of rice seedlings,height,root length,root-shoot ratio,fresh weight and dry weight decreased significantly.Net photosynthetic rate?Pn?,stomatal conductance?Gs?,intercellular CO₂ concentration?Ci?and transpiration rate?Tr?decreased significantly under single Pb stress.Under H treatment,chloroplast pigment content?Chla,Chlb,Car?,maximum photochemical quantum yield(?_P0),potential photochemical efficiency?Fv/F₀?,performance index on absorption basis(PI_ABS)and normalised total complementary area above the O-J-I-P transie?Sm?decreased significantly,and the probability that an absorbed photon is dissipated(?_D0),dissipated energy flux per reaction center?DI₀/RC?and approximated initial slope of the fluorescence transient?M₀?increased significantly.H treatment produced a positive K-band and O,J,I and P steps of fluorescence induction kinetics decreased significantly,the results showed that the oxygen-releasing complex?OEC?of rice seedling leaves were damaged.Under L treatment,jasmonate?JA?content in leaves and roots of rice seedlings increased significantly,and gibberellin?GA₃?content in leaves decreased significantly.Under H treatment,JA and abscisic acid?ABA?contents in leaves and roots increased significantly,GA₃ content in leaves and roots decreased significantly,auxin?IAA?content in leaves decreased significantly.2.Compared with AC,EC promoted the growth of rice seedlings,root length,root-shoot ratio,below-ground fresh weight,below-ground dry weight and Pn increased significantly,Gs and Tr decreased significantly.O,J,I and P steps of fluorescence induction kinetics increased significantly under EC treatment.In addition,EC treatment produced a negative K-band.Under EC treatment,zeatin?ZT?,GA₃,IAA and JA contents in leaves of rice seedlings increased significantly,and JA content in roots decreased significantly.By positively affecting OEC and increasing growth-promoting hormones,photosynthesis is strengthened and plant growth and development are positively.3.Compared with L treatment,under EC+L treatment,height,root-shoot ratio,fresh weight,dry weight,Pn,Tr and Ci increased significantly.Compared with H treatment,fresh weight,above-ground dry weight,Gs and Tr increased significantly under EC+H treatment.Compared with L treatment,J,I and P steps of fluorescence induction kinetics increased significantly under EC+L treatment.Compared with H treatment,the fluorescence induction kinetics showed the same change under EC+H treatment.Compared with AC,EC+L treatment produced a negative K-band,while EC+H treatment produced a positive K-band.Thus,high concentration of CO₂ protected OEC by increasing I,J and P steps and decreasing K-band,and then enhanced photosynthesis.Compared with L treatment,under EC+L treatment,GA₃,JA and ZT contents in leaves increased significantly,and JA content in roots decreased significantly.Compared with H treatment,under EC+H treatment,GA₃ and JA contents in leaves increased significantly,and JA content in roots decreased significantly.By increasing growth-promoting hormones,the damage of Pb stress on plant growth and metabolism are alleviated to some extent.